GEOLOGY OF THE INTERMOUNTAIN WEST an open-access journal of the Utah Geological Association ISSN 2380-7601 Volume 12 2025 This is an open-access article in which the Utah Geological Association permits unrestricted use, distribution, and reproduction of text and figures that are not noted as copyrighted, provided the original author and source are credited. Email inquiries to GIW@utahgeology.org. A RIVER RUNS THROUGH IT—THE QUARRY SANDSTONE AND ADJACENT STRATA, DINOSAUR NATIONAL MONUMENT, UTAH Kenneth Carpenter and Louis H. Taylor GEOLOGY OF THE INTERMOUNTAIN WEST an open-access journal of the Utah Geological Association ISSN 2380-7601 Production Cover Design and Desktop Publishing Douglas A. Sprinkel Cover An outcrop of the Quarry Sandstone in the Brushy Basin Member of the Upper Jurassic Morrison Formation located east of the Quarry Exhibit Hall, Dinosaur National Monument, Utah. i Become a member of the UGA to help support the work of the Association and receive notices for monthly meetings, annual field conferences, and new publi- cations. Annual membership is $30 and annual student membership is only $5. Visit the UGA website at www.utahgeology.org for information and membership application. The UGA board is elected annually by a voting process through UGA members. However, the UGA is a volunteer-driven organization, and we welcome your voluntary service. If you would like to participate please contact the current president or committee member corresponding with the area in which you would like to volunteer. 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Lund Utah Geological Survey, Emeritus 435.590.1338 williamlundugs@gmail.com Editors GEOLOGY OF THE INTERMOUNTAIN WEST an open-access journal of the Utah Geological Association Volume 12 2025 25 ABSTRACT This study investigates the depositional environment, sedimentological dynamics, and tectonic influ- ences that shaped the Quarry Sandstone within the Brushy Basin Member of the Upper Jurassic Morrison Formation in Dinosaur National Monument, Utah. Characterized by laterally extensive, multistory sand- stone bodies, the origin of the Quarry Sandstone has been a subject of ongoing debate. By synthesizing new field data and revisiting existing interpretations, this research challenges prevailing hypotheses and offers new perspectives on the geological history of the Morrison Formation at the Monument. Whereas the Morrison Formation, deposited in a foreland basin setting on the Colorado Plateau, is generally well understood, the Quarry Sandstone's unique width-to-thickness ratio sets it apart from other sandstone units in the Brushy Basin Member. This distinct feature suggests a depositional history that cannot be fully explained by traditional foreland basin models. To address this anomaly, the study places the sandstone within its stratigraphic framework, emphasizing the critical role of accommodation space in shaping its deposition. A key finding of this research is the proposed influence of a proto-Split Mountain anticline on the sedimentation patterns of the Quarry Sandstone. This minor structural feature, likely generated by oblique compressional forces associated with regional tectonics on the Colorado Plateau, appears to have played a pivotal role in reducing accommodation space during the deposition of the sandstone. Evidence for this reduction includes localized thinning of stratigraphic units and increased lateral connectivity of braided channel sandstones. The structural uplift caused by the proto-Split Mountain anticline likely created an asymmetrical dep- ositional setting. This uplift restricted accommodation, triggering a transition in fluvial systems from sin- gle-threaded sinuous channels to multithreaded braided rivers with frequent avulsions. The interconnect- ed nature of these braided channels over time reshaped sediment distribution patterns, producing the distinctive characteristics of the Quarry Sandstone. A River Runs Through It—The Quarry Sandstone and Adjacent Strata, Dinosaur National Monument, Utah Kenneth Carpenter1 and Louis H. Taylor2 1Museum of Natural History, University of Colorado, Boulder, CO 80309 USA; Kenneth.Carpenter-1@colorado.edu 2Littleton, CO 80128 USA; loutaylor44@aol.com Citation for this article. Carpenter, K., and Taylor, L.H., 2025, A river runs through it—the Quarry Sandstone and adjacent strata, Dinosaur National Monument, Utah: Geology of the Intermountain West, v. 12, p. 25–74, https://doi.org/10.31711/giw.v12.pp25-74. INTRODUCTION The Morrison Formation, an extensive Upper Ju- rassic sedimentary succession in the Western United States, is renowned for its rich paleontological record and diverse depositional environments set within a foreland basin. Stretching from southern Alberta and Saskatchewan, Canada to New Mexico, United States, and encompassing over 1.8 million km2, this forma- tion offers a unique opportunity to study a variety of 26 A River Runs Through It—The Quarry Sandstone and Adjacent Strata, Dinosaur National Monument, Utah Carpenter, K., and Taylor, L.H. Geology of the Intermountain West 2025 Volume 12 sedimentological processes and depositional settings. Morrison Formation stratigraphy features an array of lithologies, including fluvial sandstones, lacustrine mudstones, limestones, and overbank deposits, which collectively record the interplay of terrestrial and aquat- ic environments during the Late Jurassic period. Historically, research on the Morrison Formation has focused primarily on its extraordinary dinosaur fossils since their earliest discoveries in 1877 (Cope, 1877; Marsh, 1877). However, recent advancements in sedimentology have expanded the emphasis toward understanding the depositional environments and sed- imentary processes that contributed to the formation's geological complexity. These environments are inter- preted to include meandering and braided river sys- tems (e.g., Kjemperud et al., 2008; Hayden and Lamb, 2020), distributive fluvial systems (e.g., Weissmann et al., 2013; Owen et al., 2015), floodplains (e.g., Demko et al., 2004), lakes (e.g., Dunagan and Turner, 2004), and rare aeolian dunes (e.g., Peterson, 1994; Demko et al., 2004), each imparting distinct sedimentary structures and lithofacies. Detailed sedimentological analysis of these deposits reveals critical insights into the paleocli- matic conditions, paleohydrology, and tectonic influ- ences that shaped the Morrison landscape (see papers in Carpenter et al., 1998; Turner and Peterson, 1998; Turner et al., 2004; Foster and Lucas, 2006). A comprehensive sedimentological study involves the examination of grain size distributions, sedimen- tary structures, facies associations, and stratigraphic relations. These analyses help reconstruct paleoenvi- ronments and elucidate the dynamic processes respon- sible for sediment deposition. With this in mind, we investigated the unusual ridge of sandstone in which the world-famous dinosaur quarry is developed at Di- nosaur National Monument, Utah. The quarry original- ly occupied about 130 m of the 1500-m-long discon- tinuous sandstone ridge, which lies near the middle of the mudstone-dominated Brushy Basin Member of the Morrison Formation. This study investigated the rela- tions among the stratigraphic architecture, sedimentary processes, accommodation, and depositional environ- ment of the sandstone ridge in the context of the Brushy Basin. Examining how these factors interact provides a deeper understanding of the geological history and the conditions that led to the formation of the sandstone ridge and the preservation of dinosaur fossils within it. GEOLOGICAL SETTING The study area is on the southern side of Split Moun- tain, on the southeastern flank of the east-west trend- ing Uinta Mountains in northeastern Utah (Figure 1). These mountains, also known as the Uinta arch or Uinta anticline, mark the northern boundary of the Colorado Plateau. Split Mountain is an anticline associated with the Uinta Mountains and is crossed by the Green River (Figure 2A), providing extensive exposures of Paleozoic and Mesozoic strata (Rowley et al., 1979; Sprinkel, 2019; Gregson et al., 2024). The Morrison Formation, well exposed around the nose of the Split Mountain anticline, extends into the Yampa Plateau and Blue Mountain areas within Dino- saur National Monument, across the Utah-Colorado border (Figure 2B). The study area is specifically near the historic Carnegie Dinosaur Quarry, now housed within the Quarry Exhibit Hall (QEH), between Dou- glass Draw to the west and Swelter Shelter Draw to the east (Figure 2C). The famous dinosaur quarry is at the western end of the discontinuous sandstone ridge, which extends approximately 1.5 km through the Brushy Basin Member (Figure 3B). Referred to as the Quarry Sandstone here, this sandstone is the “quarry interval” of Turner and Peterson (1992a, 1992b) and “Quarry Sandstone” of Carpenter (2013) and Brezinski and Kollar (2018). Unusual for its lateral extent within the Brushy Basin Member, this sandstone and adjacent mudstone, are the focus of this study. STUDY METHODS We measured sections by tape and Brunton com- pass on both the east and west side of the QEH and through the thickest part of the remaining sandstone within the QEH (Figure 4). We integrated these sections with measured sections made by Fred (“Pete”) Peterson (formerly of the U.S. Geological Survey) and shared with us (Figures 5 and 6). Peterson made his sections in 1991 using benchmark 4992.8 on the east side of the QEH for horizontal and vertical control. Peterson's sec- tions averaged 30 m apart and connected laterally with 27 A River Runs Through It—The Quarry Sandstone and Adjacent Strata, Dinosaur National Monument, Utah Carpenter, K., and Taylor, L.H. Geology of the Intermountain West 2025 Volume 12 key beds and scour surfaces (Turner and Peterson, 1992a, 1993). Peterson made another stratigraphic section 550 m west of the QEH in Douglass Draw, which was des- ignated as the primary or master stratigraphic reference section for the Morrison Formation by Turner and Peter- son (1999) for their biostratigraphy of dinosaur localities (see STRATIGRAPHIC SETTING). We used photographs taken at different times during the 1930s by various National Park Service employees, especially geologist Albert Boyle overseeing work crews of the Federal Emergency Relief Administration (FERA) and later the Work Progress Administration (WPA) (Carpenter, 2018), to reconstruct the now missing in- terval of strata that overlaid the fossil-bearing sandstone beds. This interval of strata was considered overburden and was removed from 1934–1938 by FERA and WPA crews as part of the National Park Service's early de- velopment of what was to become the dinosaur quarry exhibit. These photographs and cited reports containing strata descriptions are housed in the archives of Dino- saur National Monument. Other photographs, mostly by Boyle, are housed in the Uintah County Regional History Center, Vernal, Utah. Correspondence of Earl Douglass is in the archives of the Carnegie Museum of Natural History, Pittsburgh, Pennsylvania. Diane Iver- son, granddaughter of Earl Douglass provided photo- graphs of Earl Douglass through Sue Ann Bilbey and Evan Hall (both Uinta Paleontological Associates, Inc., Vernal, Utah). We collected oriented hand samples in the trench- es made for the measured sections on the west and east sides of the QEH, the samples are plotted on the measured sections in Figure 4. Rock color is based on the Munsell (2009) hue, value, and chroma rock color Figure 1. Map showing the Uinta Mountains of northeastern Utah and the location of Split Mountain and Dinosaur Na- tional Monument. 28 A River Runs Through It—The Quarry Sandstone and Adjacent Strata, Dinosaur National Monument, Utah Carpenter, K., and Taylor, L.H. Geology of the Intermountain West 2025 Volume 12 scheme. Wagner Petrographic (Lindon, Utah) made the thin sections of these samples. These and other thin sections are referenced below by their catalog numbers prefaced by DINO. The thin sections are curated in the Dinosaur National Monument collections stored at the Utah Field House of Natural History State Park Muse- Figure 2. (A) Split Mountain anticline. (B) Outcrop map of the Morrison Formation in and around Dinosaur National Mon- ument of Utah and Colorado. (C) Distribution of the Quarry Sandstone in relation to the Quarry Exhibit Hall (QEH) and named drainages referenced in the text. 29 A River Runs Through It—The Quarry Sandstone and Adjacent Strata, Dinosaur National Monument, Utah Carpenter, K., and Taylor, L.H. Geology of the Intermountain West 2025 Volume 12 um in Vernal, Utah. Samples of the Quarry Sandstone were obtained from matrix still adhering to dinosaur bones collected by the Carnegie Museum crews between 1909–1922. These thin sections are listed by the bone catalog number prefaced by CM and are housed at the Carnegie Museum of Natural History, Pittsburgh. Car- penter (2013) previously described some of these thin sections. The exact stratigraphic levels of these samples are unknown, but they are assumed to be in the lower two sandstone beds from which most dinosaur bones were excavated. In addition, we collected hand samples from the Morrison Formation along the north and west sides of Split Mountain anticline during our search for the upstream part of the fluvial system that deposited the Quarry Sandstone. No thin sections of these latter samples were made. We polished most of the cut surfaces of the sam- ples to reveal internal texture. Mudstone samples were hand-polished dry using progressively finer grit sand- paper. The polished faces and whole mounts of thin sec- Figure 3. (A) Strata and distribution of sandstone beds in the study area. Abbreviations: Jmb – Brushy Basin Member; Jms + Jmt – Salt Wash and Tidwell Members; Jw + Js – Windy Hill and Stump Formations; Kcm + Km – Cedar Mountain and Mud- dy Formations; QEH – Quarry Exhibit Hall; QSs – Quarry Sandstone. Satellite view from Google Earth. (B) 180° panorama of the Quarry Sandstone from Neilson Draw to Swelter Shelter Draw. (C) Quarry Sandstone (indicated by arrows) from Dou- glass Draw, viewed eastward. (D) Quarry Sandstone (indicated by arrows) from the Quarry Exhibit Hall parking lot, viewed eastward (Neilson Draw). (E) Abrupt contact between the lowest Quarry Sandstone and underlying muddy sandstone beds. Photograph by Earl Douglass (Carnegie Museum) on the east-end of the quarry viewed west. Date of photograph unknown. 30 A River Runs Through It—The Quarry Sandstone and Adjacent Strata, Dinosaur National Monument, Utah Carpenter, K., and Taylor, L.H. Geology of the Intermountain West 2025 Volume 12 Figure 4. Stratigraphic sections in and near the QEH, showing the location of the thin sections. DINO 45156 and 45157 are 1.2 m below the bottom of the west side column. Detailed descriptions of the thin sections are included in Appendices 1 and 2. The term DINO is not shown on the stratigraphic section because of space constraints. 31 A River Runs Through It—The Quarry Sandstone and Adjacent Strata, Dinosaur National Monument, Utah Carpenter, K., and Taylor, L.H. Geology of the Intermountain West 2025 Volume 12 tions are illustrated to show macroscopic features (Fig- ure 7). Usually, these are subtle in color differences and were enhanced by darkening the image and increasing contrast. Micrographs of thin sections were not en- hanced. The thin sections and a portion of the associ- ated hand samples were subjected to hydrochloric acid (HCl) and Alizarin Red-S stain to identify and enhance the presence of calcite. Potassium ferricyanide stain was used on some sandstone thin sections to reveal ferroan dolomite cement. We conducted a petrographic examination using a Zeiss Photoscope III petrographic microscope. Thin section examinations provided overall lithology, miner- alogy (including clay content), grain size, grain round- ness, and sorting data. Examination of the carbonate samples provided overall lithology, crystal or allochem size, and fossil content. Petrographic examinations also included identification of diagenetic features. This in- formation is shown in table format in the Appendices, as are figures of all of the thin sections. Mudstone with modifiers refers to a spectrum of fine-grained sedimen- tary rock in which 50% or more of its grains are mud (calcite, clay and silt) size (Potter et al., 2005; Lazar et al., 2022). Clay particles are 4 μm or less in diameter, whereas silt particles range from 4 to 62.5 μm in diam- eter. Whole rock mudstone terminology is based on Macquaker and Adams (2003) and Lazar et al. (2022). Grain size identification follows the Udden-Wentworth scale as included in Ehlers and Blatt (1982) and Blair and McPherson (1999), among others. A Th-corrected 206Pb/238U CA-ID-TIMS zircon date reported below on a tuff we collected in the west trench was analyzed by Kevin Chamberlain, Department of Geology, University of Wyoming. Chronostratigraphic age names are those of the International Chronostrati- graphic Chart v2023/09 (www.stratigraphy.org). STRATIGRAPHIC SETTING The Morrison Formation, prominently displayed on the Colorado Plateau, consists of the thinly bedded siltstone and mudstone beds of the Tidwell Member, which is overlain by the sandstone-dominated Salt Wash Member, and capped by the gray or variegated mud- stone-dominated Brushy Basin Member (Figure 8A). Figure 5. Stratigraphic section of the Morrison Formation and adjacent strata along Douglass Draw. Redrawn from a section provided by Fred Peterson (U.S. Geological Survey). Clay data from Bilbey (1992). 32 A River Runs Through It—The Quarry Sandstone and Adjacent Strata, Dinosaur National Monument, Utah Carpenter, K., and Taylor, L.H. Geology of the Intermountain West 2025 Volume 12 These three members are present in Dinosaur National Monument (Turner and Peterson, 1991, 1992b, 1999); however, the distinction between members can be chal- lenging due to the scarcity of resistant sandstone beds within the Salt Wash Member as initiatlly observed by Stokes (1944) (Figures 8B and 8C), and the Tidwell Member was not recognized by Bilbey et al. (1974) in the Monument. In the study area, the Morrison Formation is most extensively exposed in Douglass Draw, oriented per- Figure 6. Stratigraphic profile of the Quarry Sandstone from the QEH to near Swelter Shelter Draw. The profile shows that the Quarry Sandstone consists of stacked and coalesced fluvial sandstone beds. Courtesy of Fred Peterson, U.S. Geological Survey 33 A River Runs Through It—The Quarry Sandstone and Adjacent Strata, Dinosaur National Monument, Utah Carpenter, K., and Taylor, L.H. Geology of the Intermountain West 2025 Volume 12 pendicular to the formation's strike, and designated as a primary reference section by Turner and Peterson (1999). Here, the Tidwell Member measures approxi- mately 10 m in thickness, the Salt Wash Member ap- proximately 74.8 m, and the Brushy Basin Member ap- proximately 100 m thick (Figure 5). Tidwell Member The Tidwell Member is poorly exposed in the study area (Figures 8A and 8B). Where visible, it comprises interbedded moderate reddish-brown (10R 4/6 of the Munsell color scheme) and pale greenish-yellow (10Y 8/2) mudstone, along with white (N9) fine-grained sandstone and siltstone. Near the base, many areas fea- ture a zone of red botryoidal authigenic chert, which Peterson (1988) identified as a widespread marker unit on the Colorado Plateau. Carpenter (2022), however, found its distribution to be inconsistent. Marine dino- flagellates reported from the Tidwell Member near the quarry (Turner and Peterson, 1999) are actually from the Redwater Member of the Stump Formation (Turner and Peterson, 1992b, p. 88; Litwin et al., 1998, p. 302). Currently, compelling evidence for a marine influence on the Tidwell Member is lacking. The Tidwell Member serves as the base of the Mor- rison Formation across the Colorado Plateau (O'Sul- livan, 1984; Peterson, 1988; Carpenter, 2022). In the Rainbow Draw area north of Split Mountain (Figure 2A), a volcanic ash layer within the Tidwell has a reca- librated 40Ar/39Ar age of 156.84 ± 0.59 Ma (middle Ox- fordian) (Trujillo and Kowallis, 2015), closely matching the 156.77 ± 0.55 Ma age abtained 2.4 m above the base of the Tidwell near Notom, Utah, 290 km farther south on the plateau (Trujillo and Kowallis, 2015). The Windy Hill Formation (originally the Windy Hill Member of the Sundance Formation, Pipiringos, 1968), which underlies the Tidwell Member, has at times been considered a basal member of the Morrison Formation (Peterson, 1994; Sprinkel et al., 2019). How- ever, we regard it as a separate formation, following the reasoning put forth by Danise and Holland (2018) and Holland and Wright (2020) (see Wroblewski and Mor- ris, 2022, for a dissenting position). Our field work in the formation has yielded a section of sauropod rib in the Orchard Draw drainage, 1250 m west of the QEH. It is the first reported dinosaur bone from this formation in the Monument; pterosaur and sauropod tracks have been reported from Wyoming (e.g., Meters et al., 2009; Meyers and Breithaupt, 2014). Salt Wash Member The coarse-grained sandstone beds of the Salt Wash Member exhibit greater prominence in Douglass Draw (Figure 8B) compared to east of the QEH, where rapid weathering due to higher clay content is evident (Figure 8C). These sandstone beds, ranging from white to very light gray (N9–N8), are interbedded with non-swelling, moderate orange-pink to moderate red (10R 7/4–5R 4/6) mudstone. In Douglass Draw, the lower boundary of the Salt Figure 7. Comparison of unenhanced (A) and enhanced (B) miscrohotographic images, illustrating subtle macro-features as a function of color in the whole slide sample. 34 A River Runs Through It—The Quarry Sandstone and Adjacent Strata, Dinosaur National Monument, Utah Carpenter, K., and Taylor, L.H. Geology of the Intermountain West 2025 Volume 12 Wash Member is marked by a white to very light gray (N9–N8) muddy sandstone at the base, juxtaposed against a very pale orange (10YR 8/2) muddy sandstone of the underlying Tidwell Member (Figure 8B). The upper boundary of the Salt Wash Member is identified by a similar white to very light gray (N9–N8) muddy sandstone or a moderate red (5R 4/6) mudstone just below a moderate orange-pink to moderate reddish-or- ange (10R 7/4–10R 6/6) mudstone of the Brushy Basin Member (Figure 8B). Archival photographs show that the boundary between the Salt Wash and Brushy Basin Members lies in the axis of the valley currently under- lying the road from the lower parking lot to the upper parking lot at the QEH. Around Dinosaur National Monument, the Salt Wash Member is at the edge of its recognizable extent on the Colorado Plateau. Sprinkel et al. (2019) identi- fied the northernmost recognizable occurrence of the Salt Wash Member in the Rainbow Draw area north of the Split Mountain anticline (Figure 2B). Beyond this region, sandstone beds no longer distinctly delineate the Salt Wash Member, leading to its mapping as “un- differentiated” within the Morrison Formation (Mul- lens and Freeman, 1957). Within Dinosaur National Monument, the Salt Wash Member is interpreted as part of the “claystone and lenticular sandstone facies” of a distal part of an alluvial megafan (Craig et al., 1955, 1977) or more re- cently as a distributive fluvial system (Weissmann et al., 2013; Owen et al., 2015, 2017). However, Carpen- ter (2022) raised significant concerns regarding these interpretations based on paleocurrent data across the entire Colorado Plateau. Brushy Basin Member The Brushy Basin Member on the Colorado Plateau constitutes a thick slope-forming unit rich in clay and notably lacking in sandstone, contrasting sharply with the underlying Salt Wash Member (e.g., Figure 8A). The majority of the Brushy Basin Member mudstone beds are composed of montmorillonite clay formed through the alteration of volcanic ash (Keller, 1962). Robinson and McCabe (1998) attributed the abrupt lithofacies shift from the sandstone-dominated Salt Wash Member to the mudstone- or claystone-dominated Brushy Ba- sin Member to changes in watershed hydrology driven by climate or tectonism, with Currie (1997) suggest- ing concomitant changes in fluvial dynamics. Howev- er, Heller et al. (2015) found little difference in paleo- channel architecture between the Salt Wash and Brushy Basin Members in southeastern Utah, proposing that reduced channel-belt stacking in the Brushy Basin re- sulted from decreased avulsion frequency, potentially Figure 8. (A) Typical Morrison Formation on the north-central Colorado Plateau, featuring erosion-resistant, ledge-form- ing sandstone beds in the Salt Wash Member, positioned between the underlying siltstone of the Tidwell Member and the overlying mudstone of the Brushy Basin Member (38.7982°N., -109.9867°W.; type location of the Salt Wash Member). (B) Morrison Formation in Douglass Draw, characterized by a few ridges of erosion-resistant sandstone beds in the Salt Wash Member (40.4419°N., -109.3084°W.). (C) Salt Wash Member east of the QEH, showing the absence of resistant sandstone (40.4404°N., -109.2934°W.). Abbreviations: Jmb – Brushy Basin Member, Morrison Formation; Jms – Salt Wash Member, Morrison Formation; Jmt – Tidwell Member, Morrison Formation. 35 A River Runs Through It—The Quarry Sandstone and Adjacent Strata, Dinosaur National Monument, Utah Carpenter, K., and Taylor, L.H. Geology of the Intermountain West 2025 Volume 12 linked to increased volcanic ash input as airfall or wash- load in rivers. Dawson (1970) also linked the abrupt de- crease in clastics to volcanism, specifically the burial of clastic sources by volcanic deposits. Despite differing causal interpretations, the transi- tion between the Salt Wash and Brushy Basin Members is diachronous (Kjemperud et al., 2008) relative to a mid-Morrison unconformity often represented by a pa- leosol at the top of the Salt Wash Member (Demko et al., 2004). This paleosol or unconformity, however, is not universally present (Kjemperud et al., 2008; Heller et al., 2015; Maidment and Muxworthy, 2019), and evidence for large-scale incisions or paleovalleys (Demko et al., 2004) was not noted by Currie (1997), nor have we seen such structures in the study area. Within Dinosaur National Monument, the Brushy Basin Member may be informally subdivided into a dis- continuous lower unit exhibiting red and white weath- ering and an upper unit exhibiting gray weathering (Figure 9; Turner and Peterson, 1999). The lower unit, approximately 12 m thick, predominantly exhibits hues ranging from grayish-pink (5R 8/2) to light-red (5R 6/6) and lacks the popcorn or frothy texture of weathered smectitic clay. This unit is overlain by an upper unit, 83 m thick, weathering from light-gray (N8) to medi- um-gray (N5) mudstone characterized by the popcorn texture of weathered smectite, the predominant clay in the Brushy Basin Member (Keller, 1962; Bilbey et al., 1974; Owen et al., 1989; Heller et al., 2015). In its un- weathered state, this silty clay-rich mudstone appears grayish-black (N2). The sandstone housing the dino- saur quarry is about 43 m above the Salt Wash Member. The color and texture distinctions in the lower Brushy Basin Member observed by Turner and Peter- son (1992a, 1999) seem to correlate with their hypoth- esized Morrison clay change marker representing a shift from non-swelling illitic clays to swelling smectitic clays. However, such a clay change was not confirmed by X-ray diffraction analysis of clays near the QEH by Bilbey (1992), which revealed a mix of montmorillon- ite-illite (smectite-illite) clays in this interval (Figure 5). Trujillo (2006) suggested that the differing weath- ering patterns observed by Turner and Peterson are a reflection of the proportion of silt and sand grains, with amounts greater in the “illitic”-looking weather pro- file. This seems to be the case in the study area, where the lower unit is associated with multiple thin gravel- ly crevasse splays or levee deposits traceable laterally into channel sandstone beds along the road to the QEH (Figure 9B). The upper contact (K-1 unconformity) of the Brushy Basin Member across much of the western part of the northern Colorado Plateau is marked by the base of the chert-rich, cobble- to boulder-containing Buck- horn Conglomerate Member of the Lower Cretaceous Cedar Mountain Formation (Kirkland et al., 2016). In areas where the conglomerate is absent, this boundary is identified at the top of a mottled yellow-orange mud- stone paleosol bearing chert pebbles below the lower- most calcrete bed, separating smectitic, generally red or gray mudstone of the Brushy Basin Member, from the non-smectitic, pastel-colored mudstone of the Ce- dar Mountain Formation (Figure 10A; Sprinkel et al., 2012; Kirkland et al., 2016). Near the QEH, where the conglomerate is absent, the contact is found at the top of yellow-orange to moderate red mudstone, typically situated 1 to 3 m below a sporadically occurring cal- crete paleosol (Figure 10B; Kirkland and Madsen, 2007; Chure et al., 2010; Sprinkel et al., 2012, 2019). Currie (1997) identified the top of this calcrete as the K-1 contact, indicating that a Cretaceous paleosol developed within the top of the Brushy Basin Member during a hiatus in sediment deposition. In contrast, Brezinski and Kollar (2018) placed the K-1 boundary at the base of the calcrete, positioning the paleosol and its host sediments entirely within the Cedar Mountain Formation, implying a second hiatus with calcrete for- mation in earliest Cretaceous sediments. This calcrete, discontinuous and thinning out approximately 600 m east and 320 m west of the QEH, is insufficient evidence alone to determine the boundary placement, as the low- er Cedar Mountain Formation contains several discon- tinuous calcrete beds (Kirkland et al., 2016). At least three such beds are present in the lower Cedar Moun- tain Formation along Douglass Draw (Figure 10C). Locating the yellow-orange to moderate red mudstone K-1 contact at Dinosaur National Monument can be challenging due to soil creep on steep slopes, though visible where erosion maintains clean exposures. 36 A River Runs Through It—The Quarry Sandstone and Adjacent Strata, Dinosaur National Monument, Utah Carpenter, K., and Taylor, L.H. Geology of the Intermountain West 2025 Volume 12 LITHOFACIES DESCRIPTION Sandstone Facies The distribution of sandstone lenses in the Brushy Basin Member within the study area is depicted in Fig- ure 3A. Although there are a few isolated lenticular sandstone bodies, most sandstone occurs in a narrow interval 3 to 9 m thick, forming a discontinuous ridge created by the Quarry Sandstone extending eastward from the QEH (Figures 3B, 3D, and 6). This sandstone bed can be traced westward to Douglass Draw, although erosion has not yet made it a prominent ridge (Figure 3C). The bases of the sandstone bodies are typically scoured into the underlying strata, resulting in abrupt contacts (Figure 3E). These underlying strata generally consist of sandy mudstone or muddy sandstone, which is generally white and easily recognizable from a dis- tance. The Quarry Sandstone bed dips to the south, with reported values varying as follows: 50° (Hansen et al., 1983), greater than 55° (Brezinski and Kollar, 2018), 60° (E. Douglass correspondence to Assistant Direc- tor Douglas Stewart, Carnegie Museum, September 24, 1909), 60 to 70° (Turner and Peterson, 1992a), 62° (Car- penter, 2013), 65° (Boyle, 1938a), and 67° (Untermann and Untermann, 1954; Bilbey, 1992; Lawton, 1977). These differences can be partly explained by the loca- tions where the dips were measured in and around the QEH and in Neilson Draw. Carpenter (2013) measured the dip on the flat sandstone surface on the east side of the QEH, and Boyle (1938a) on the rock face formerly Figure 9. (A) Brushy Basin on the north side of the QEH, showing the lower red and white unit overlain by the gray unit. (B) Another view showing the red and white unit grading into channel sandstone. The red line connects the same sandstone bed (40.4411°N., -109.3014°W.). 37 A River Runs Through It—The Quarry Sandstone and Adjacent Strata, Dinosaur National Monument, Utah Carpenter, K., and Taylor, L.H. Geology of the Intermountain West 2025 Volume 12 present on the west side of the QEH (“Dinosaur Peak”). Other measurements in the vicinity include 48° near the crest of the divide east of the QEH (Hansen et al., 1983); 50° on the east side of Camp Gulch (Rowley et al., 1979) and 62 to 68° east of the QEH along the Quar- ry Sandstone (Lawton, 1976). Isolated Sandstone Bodies Although the emphasis of this study is on the Quar- ry Sandstone bed, for thoroughness and context, we briefly describe the few isolated lenticular sandstone bodies in the study area that occur below or above the Quarry Sandstone bed. Such isolated bodies are more common in the Brushy Basin Member than in the stacked sandstone bodies that dominate the Salt Wash Member (Currie, 1997; Galli, 2014; Heller et al., 2015). The isolated sandstone bodies are represented in the study area by two types of lithologies. An example of Type 1 is approximately 27 m above the Salt Wash Mem- ber (Figures 11A and 11B). It is light-brown (5YR 5/6) to pale-yellowish-orange (10YR 8/6), coarse-grained to conglomeratic litharenite with quartz predominating as the coarse-grain fraction. The larger granule-to-pebble- size clasts are gray chert and some potassium feldspar. The brown tint is most likely due to iron hydroxide. An example of Type 2 occurs about 10 m below the Cedar Mountain Formation (Figure 11C). It is a litharenite of quartz sand and polychromatic chert conglomerate, much like the Quarry Sandstone, with silica and calci- um carbonate cements. These isolated coarse-grained bodies are narrow, and have a width/thickness (w/t) ra- tio (less than 4:1). Stacked Sandstone Bodies (Quarry Sandstone) The Quarry Sandstone, about 43.9 m above the Salt Wash Member, is composed of discontinuous multi- story sandstone bodies that are predominantly stacked conglomeratic or coarse- to fine-grained sandstone, and are white (N9) to very light gray (N8). These bod- ies weather to pale yellowish-orange (10YR 8/6) to pale reddish-brown (10R 5/4) due to the weathering of iron disseminated in pore spaces (Hubert et al., 1996) in con- junction with desert varnish (Figure 12A; see also cover photograph). The geometries of the stacked sandstone bodies are best seen in the QEH, where three major sets are exposed; at least one additional poorly cemented sandstone bed was mostly removed to expose the fossil bones in the lower sandstone for public viewing; this sandstone is mostly described from reports before it was removed beginning in the early 1950s. The three remaining sandstone beds in the QEH are generally similar except as noted in the following. The lowest sandstone is conglomeratic near the base, fining upwards, and varies in thickness from 0.6 to 1.8 m (Walker, 1943). Fossil bones occur but are mostly widely dispersed. The second and third sandstone beds, treated as a single sandstone by Walker (1943), are con- glomeratic or coarse-grained at the base and fine up- wards; combined, they vary in thickness from 2.4 to 3 Figure 10. (A) Jurassic-Cretaceous boundary on the Colorado Plateau at Horse Bench (38.8534°N., -110.2201°W.). (B) Ju- rassic-Cretaceous boundary near the QEH (40.4402°N., -109.3012°W.). (C) Three carbonate beds (calcretes) near the base of the Cedar Mountain Formation at Douglass Draw (40.4408°N., -109.3081°W.). Abbreviations: Jmb – Brushy Basin Member; Kcm – Cedar Mountain Formation. 38 A River Runs Through It—The Quarry Sandstone and Adjacent Strata, Dinosaur National Monument, Utah Carpenter, K., and Taylor, L.H. Geology of the Intermountain West 2025 Volume 12 m. However, as Walker noted, there are two bone levels within this sandstone, implying two depositional cycles, thus it is actually two stacked sandstone beds. On the quarry face today, these sandstone beds are separated by a clay drape, which was not noted by Walker (1943). The grains of the three sandstone beds are predom- inantly subrounded to well-rounded, medium- to very- coarse-grained monocrystalline quartz and black chert (approximately 25+%), giving the sandstone a salt-and- pepper appearance (Figure 12B), hence the gray tint from a distance. This litharenite, referred to as a chert arenite by Bilbey et al. (1974), has matrix-supported larger particles that are commonly coarse-sand to peb- ble-size, angular to subrounded grayish-black (N2) or light-gray (N7) to very light gray (N8) chert (Figure 12C), or subrounded to rounded clasts of carbonate siltstone or mudstone that are occasionally up to cobble size (Figure 12D). These fine-grained clasts (siltstone or mudstone, referred to as devitrified tuff fragments by Bilbey et al., 1974) are less resistant to erosion, creating a pock-marked weathered surface (Figure 12E). Pockets of fine- to medium-grained white (N9) sandstone also occur within the conglomeratic sandstone bodies (Fig- ure 12F). The pockets are often lobate and superficially resemble ball-and-pillow structures but are not con- nected to underlying mudstone. These do not appear to be transported fine sediment clasts but rather scour in- fill in the low-pressure, low-velocity recirculation zone on the downstream side of the scour crest during the waning phase of river flow (Figure 12G). Magnetite is rare, indicating a non-igneous, non-met- amorphic source for the sand. Chalcedony and calcite are the predominant cements (Bilbey et al., 1974; Lawton, 1977; Hubert et al., 1996), although potassium ferricy- anide staining reveals some ferroan dolomite cement in some sandstone adhering to bones collected by the Car- negie Museum (Carpenter, 2013). Chalcedony is a com- mon sandstone cement where glassy volcanic ash is pres- ent because the thermodynamically unstable hydrous silica of the glass shards dissolves and reprecipitates in this more stable form (Worden and Morad, 2000). The abundance of volcanic ash characterizes the mudstone in the Brushy Basin Member and sets it apart from the other members of the Morrison Formation (Keller, 1962; Heller et al., 2015). At Dinosaur National Monument, at least 42 predominantly rhyolitic volcanic ash beds span- ning 2.2 million years are present in the Brushy Basin Member both above and below the Quarry Sandstone (Christiansen et al., 2015), thus providing a ready source of soluble silica. Additionally, the chalcedony-cemented sandstones tend to have little interstitial clay because clay inhibits quartz cementation (Worden and Morad, 2000). Large masses of chalcedony occur in sandstone at various places along the Quarry Sandstone. Bedforms were revealed through erosion and quar- rying along bed partings. These include wedge-shaped channel bars having a gently sloped stoss side and steep lee side (Figure 13A); these can be seen in photographs taken during the excavations (Figure 13B). These bed- forms are rarely larger than 10 to 30 cm thick. The larg- est is preserved in the thickest remnant of the Quarry Sandstone today in the west half of the QEH (Figure Figure 11. Lenticular sandstone facies. (A) Type 1 brown coarse-grained and conglomeratic litharenite (40.4408°N., -109.2990°W.). (B) Close-up showing quartz sand matrix and pebbles of chert and potassium feldspar. Scale in cm. (C) Type 2 quartz and chert conglomeratic litharenite with silica and carbonate cements. 39 A River Runs Through It—The Quarry Sandstone and Adjacent Strata, Dinosaur National Monument, Utah Carpenter, K., and Taylor, L.H. Geology of the Intermountain West 2025 Volume 12 13C). On the west side of the bar, a juvenile sauropod pelvis is preserved standing vertically through the de- posit, indicating that sediment deposition was rapid (Figure 13D; Carpenter, 2020a). This mega-bedform is unusual for its height, being about 152 cm, and may have formed as a bank-attached bedform deposited in the thalweg. The predominant sedimentary structure of the Quarry Sandstone is trough cross-stratification. The tops of these structures can be seen on the top surfac- es of the steeply dipping Quarry Sandstone, where the softer mudstone beds have eroded away (Figure 13E). This surface typically preserves troughs in three dimen- sions, which indicate rapidly waning flows rather than the reworking of bedforms and previously deposited sediments. The same sedimentary structures are seen Figure 12. Stacked channel sandstone facies: (A) Weathered Quarry Sandstone at Neilsen Gulch (40.4402°N., -109.2997°W.). (B) Thin section CM70384 is fine- to medium-grained “salt and pepper” sandstone composed of quartz and black chert. Scale in mm. (C) Thin section CM70384 is medium- to coarse-grained quartz and chert sandstone matrix supporting an- gular to subrounded multicolored chert granules and pebbles. Scale in cm. (D) Carbonate clasts on the east side of the QEH. Scale in cm. (E) Eroded fine-grained clasts creating a pockmarked surface on the east side of the QEH. Scale in cm. (F) Finer-grained sandstone lenses (indicated by arrows) infilling troughs in coarser-grained sandstone at Neilsen Gulch (40.4402°N., -109.2997°W.). (G) Diagram illustrating finer sand deposition in the lee of a dune due to flow separation, recir- culation, and velocity drop. 40 A River Runs Through It—The Quarry Sandstone and Adjacent Strata, Dinosaur National Monument, Utah Carpenter, K., and Taylor, L.H. Geology of the Intermountain West 2025 Volume 12 Figure 13 caption is on the following page. 41 A River Runs Through It—The Quarry Sandstone and Adjacent Strata, Dinosaur National Monument, Utah Carpenter, K., and Taylor, L.H. Geology of the Intermountain West 2025 Volume 12 in archival photographs of the Quarry Sandstone before their removal during excavation (Figure 13B). High-an- gled inclined strata (a.k.a. planar stratification) are also present and are best seen on the quarry face where strings of vertebrae are draped over the slip face (Figure 13F); these inclined strata generally range from 10 to 30 cm thick. Finer-grained sandstone atop the bedforms sometimes are horizontally laminated, indicative of high-energy deposition during supercritical flow over the top of bedforms during the waning stage of flow. Also visible on the quarry face are infilled scours. Many of these are adjacent to dinosaur bones as contrasting sediment grains (Figure 13G). Flume studies have shown that scours form as a re- sult of three-dimensional flow separation (turbulence), creating areas of acceleration and deceleration. The highest values of turbulence occur in regions of high- est pressure on the bed in front of and immediately ad- jacent to an obstacle (Carpenter, 2020a) and indicate regions of flow turbulence (Kirkil and Constantinescu, 2010; Euler and Herget, 2012; Maity and Mazumder, 2014). Helical flow results due to downwards hydro- static pressure, creating a horseshoe vortex. This vortex plucks or lifts sand grains upwards into the flow, thereby causing bed erosion or scour. Deposition of the trans- ported sand occurs in the flow shadow, a region of flow deceleration and low pressure. If erosion exceeds the depth and width of the obstruction, underscour may result. Upstream scouring may cause bones to dip up- stream, thus contributing to their own burial (Figure 13H; Carpenter, 2022). Smaller bones and shells are of- ten found in what was the downstream flow shadow of larger bones (Figure 13I). The sandstone bodies are separated in places by thin pale yellowish-orange (10YR 8/6), grayish-orange (10YR 7/4), and moderate red (5R 5/4) mottled sider- itic mud drapes (Figure 13J) across gently undulatory erosional surfaces that are similar to those within com- pound bars as revealed by ground-penetrating radar (Sambrook Smith et al., 2006). These drapes were noted by Lawton (1977), Dodson et al. (1980), and Turner and Peterson (1992a). The uppermost sandstone bed (fourth sandstone bed) is treated separately because little of it remains for study. It was removed because preservation of the fossil bones was generally poor (Museum Geologist Theodore White, memorandum to Superintendent Jess Lombard, October 1, 1963). Archival color photographs and trac- es remaining in the QEH show that on the west side of the quarry, this sandstone is separated from sandstone 3 by a wedge of purple-tinted muddy sandstone or sandy mudstone (Figure 14A), but it is in contact with sand- stone 3 on the east side of the quarry (Figures 14B and 14C). Traces of sandstone 4 east of the QEH are white (N9) to very light gray (N8) and poorly cemented (Fig- ure 14C). Walker (1943, p. 7) reports that this bed was 2.4 to 3 m thick, “composed of a fine to coarse sandstone with considerable clay as a binder [i.e., muddy sand- stone]. It also has concretionary masses [recognized as indurated clay balls by Boyle, 1938b] scattered through- out… The matrix composing this … layer is very un- stable and weathers rapidly.” The sandstone on the east side of the QEH is clayey, medium sand to granule size, poorly sorted, subrounded to rounded, with mudstone Figure 13 on the previous page. (A) Linguoid dune in profile at Camp Gulch (40.4409°N., -109.3052°W.). (B) Mega-bedform in the quarry was exposed several years earlier by a rockfall noted in a letter by Earl Douglass (November 4, 1916). Photo- graph taken sometime between 1924–1929 and the bedforms have since been removed in the late 1930s by Works Progress Administration workers. (C) Mega-bedform, 1.52 m tall, on the quarry face. Arrows designate slip faces on the lee side. The box indicates the location of a dinosaur pelvis laying facedown. (D) Sketch showing how the pelvis in (C) was buried stand- ing face down. Scale in dm. (E) Scours and troughs on the top surface of Quarry Sandstone (40.4401°N., -109.2987°W.). (F) Planar face of a straight-crested bedform delineated by strings of dinosaur vertebrae as seen in the QEH. Vertebrae on or near the same slip face (sf) become horizontal on the bed bottom (b). One string of vertebrae is nearly horizontal at the top (t) of the planar dune. Note other scattered horizontal bones on the bed bottom. (G) Infilled scour (indicated by arrows) downstream of the bone. Clam (c) valves are in a stable position in the flow shadow. (H) Upstream inclination (arrow) of large bones due to under scour. Note that the bones cut across the bedding surface. (I) Small bone in the flow shadow of a larger bone (sauropod ischium). Scales in cm. (J) Sideritic stained mud drape at QEH. 42 A River Runs Through It—The Quarry Sandstone and Adjacent Strata, Dinosaur National Monument, Utah Carpenter, K., and Taylor, L.H. Geology of the Intermountain West 2025 Volume 12 or siltstone clasts that are mostly the same color as the sandstone except for an occasional surface stain of pale yellowish-orange (10YR 8/6) or dark yellow-orange (10YR 6/6). Less common clasts are of medium light -gray (N6) with flecks of black organic material. The clasts are 2 to 20 mm in diameter, rarely larger. Sheet (Tabular) Sandstone Beds Thin sheet or tabular sandstone beds are present be- low and above the Quarry Sandstone. Those below are often wedge-shaped and feathering at the edges, and are present on the east side of the QEH below the stacked sandstone beds (Figures 15A and 15B). These thin het- Figure 14. (A) Archival photograph of steeply dipping beds with view of bed tops. The purple mudstone (upper part of photograph) underlies the muddy white sandstone 4 towards the west end of the quarry. (B) Archival photograph showing sandstones 3 and 4 in contact on the east end. The kneeling person in the red circle is pointing to fossil bones. The arrow indicates the general location of (C) today. (C) Remnant of sandstone 4 on the east side of the QEH. (A) and (B) courtesy of the National Park Service, taken in the early 1950s. 43 A River Runs Through It—The Quarry Sandstone and Adjacent Strata, Dinosaur National Monument, Utah Carpenter, K., and Taylor, L.H. Geology of the Intermountain West 2025 Volume 12 erolithic sandstone wedges have abrupt and sometimes erosional bases, and internally they may exhibit one or more fining and coarsening cycles resulting from fluctu- ating flows (Figure 15C). These sandstone beds feature increasingly larger clasts from the lowest to the highest bed, with scattered matrix-supported pebbles of sub- rounded grayish-black (N2) or light-gray (N7) to very light gray (N8) cherts. The upper surfaces may also con- tain mudstone clasts or pits from clasts that have eroded out (Figure 15D). The lowest sandstone, numbered 1, is underlain by coarsening-upward muddy sandstone beds. The sandstone bodies are separated by white (N9) to very light gray (N8) muddy sandstone lenses that fine upwards (Figure 15E). Sandstones 1 and 2 (Figures 15A and 15B) are wedge shaped, become thinner in the up-dip direction, as does sandstone 4. Sandstone 3 thins in the down-dip direc- tion on the east side, where it grades into a gravelly or Figure 15. (A) Edge view of tabular sandstone beds (labeled 1 through 5) exposed on the east side of the QEH. Sandstone 3 wedges out downdip, and sandstone 4 wedges out updip. (B) Oblique view of thin-bedded sandstone of (A). The arrow indicates the location of the view in (E). (C) Sectioned sandstone 1, DINO 48398, showing fining upwards, then coarsening upwards within a narrow zone. The arrow indicates upward direction. Scale in mm. (D) Carbonate (orange) and clay (white) pebble conglomerate at the top of sandstone 4. Note pits from eroded clay nodules. (E) Fining upwards from sandstone 3 (labeled 3) to the base of sandstone 5 (labeled 5). Sandstone 4 wedges out and does not extend this far (see B). Carbonate nodules (cn) formed in the muddy sandstone beneath the sandy mudstone below sandstone 5. Scales in cm. 44 A River Runs Through It—The Quarry Sandstone and Adjacent Strata, Dinosaur National Monument, Utah Carpenter, K., and Taylor, L.H. Geology of the Intermountain West 2025 Volume 12 pebbly white (N2) to light-gray (N7) muddy sandstone. The gravel and pebbles are predominantly grayish-black and light-gray chert. Sandstone 3 can be traced west to a muddy sandstone (see Figure A1 in the Appendix 1) on the west side of the QEH and is used as the datum for correlation. This datum indicates that the base of the Quarry Sandstone is about 1 to 1.5 m lower on the east side of the QEH than on the west (Figures 4 and 10A). Sandstone 5 forms the lowermost bone-bearing sand- stone within the QEH, thus showing that these sand- stone sheets are intimately linked to the Quarry Sand- stone. The five thin sandstone beds are more resistant to erosion, being cemented with silica or calcium carbon- ate. Whereas the muddy sandstone beds between them erode more easily, leaving the harder sandstone beds projecting where they crop out. Similar thin sandstone beds are present beneath the Quarry Sandstone east of the QEH (Figure 6). Archival photographs show the now-missing tab- ular sandstone beds overlying the Quarry Sandstone (Figure 16). This area is now occupied by part of the QEH and a service road. The sandstone beds considered overburden to the underlying bone-bearing sandstone beds were described by geologist Albert Boyle (1938a, p. 13), in charge of their removal, as “fine-grained fri- able greenish sandstone…” of variable thickness. The abundance of clay in these beds can be inferred by Boyle's observation that “the sandstone sloughs down readily when slightly moistened.” The ease of slaking in water was confirmed with a small sample collected on the southwest corner of the QEH. As a result of its ease of weathering and erosion, these sandstone beds orig- inally formed the saddle on the divide between Camp Draw on the west and Neilson Draw on the east and between the silicified Quarry Sandstone and calcrete of the Cedar Mountain Formation (Figure 17). On the west side of the QEH, the boundaries of many of the stacked sandstone sets are poorly defined in contrast to the sharp base of the overall unit. Here, channel sandstone beds grade laterally with a rapid in- crease in silt and clay content over a span measured in meters (Figure 18A). In the cross section of the strata visible in the QEH foundation trench, the sandstone is conglomeratic, consisting of rounded mudstone clasts (Figure 18B) or irregular mudstone clasts in a sandstone matrix that also contains floating dark chert pebbles (Figure 18C). These muddy sandstone bodies can be traced outside the QEH as a series of three sheet sand- stone beds separated by mudstone (Figure 18D). Dino- saur bones are preserved in these sandstone beds. The most complete bone found recently is a femur (leg bone) oriented parallel to the local shallow flow in a direction away from the sandstone of the quarry (Figure 18E). The sandstone beds coarsen upwards (Figure 19A) or have an erosional base associated with the distribu- tary channel part of the sheet sandstone beds (Figure 19B). From the quarry wall in the QEH westward, there is a shift from chalcedonic to calcitic cementation of the sandstone as the clay content increases and the clay in- hibits chalcedony formation (Figure 18A), resulting in a reduction in resistance to weathering and erosion as seen in Figure 18D. Elsewhere along the ridge, areas of higher clay content are apparent in satellite imagery as light-colored soils and on the ground as gravelly or san- dy, very light gray (N8) soils that are commonly vegetat- ed and require trenching to expose the less weathered muddy sandstone. Mudstone Facies The mudstone facies are best accessed adjacent to the QEH because construction activity has removed vegetation and soil. Much of the mudstone analysis was conducted there and is representative of the mudstone bracketing the Quarry Sandstone except as noted be- low. Retallack (1997) proposed names for the paleosols mudstone facies at Dinosaur National Monument, but these have not been widely adopted (e.g., Demko et al., 2004). On the west side of the QEH is a remnant of “Di- nosaur Peak,” a topographic high point named by Earl Douglass. The east face is cut perpendicular to the strike, exposing the mudstone beds immediately be- low the Quarry Sandstone. At 4 m below the Quarry Sandstone, there is an abrupt color and textural change from a silty mudstone to a sandy mudstone unit (Figure 20A). Archival photographs of a less weathered surface show that the lower mudstone had a thin, light-colored ash bed or thin strings of light-colored sandstone (Fig- ure 20B). The lower mudstone (Figures 20C and 21A) 45 A River Runs Through It—The Quarry Sandstone and Adjacent Strata, Dinosaur National Monument, Utah Carpenter, K., and Taylor, L.H. Geology of the Intermountain West 2025 Volume 12 is predominantly medium dark-gray (N4). In polished cross section, however, the mudstone is polychromat- ic in color, including pale greenish-yellow (10Y 8/2), pale yellowish-green (10GY 7/2), very light gray (N8) to medium gray (N5), and even a little moderate pink (5R 7/4). These colors accentuate extensive bioturba- tion, including possible rhizoliths (Figure 21B). The up- per sandy and silty mudstone is light gray (N7) (Figure 20D). This sandy mudstone facies correlates with the zone of muddy sandstone and tabular sandstone on the east side of the QEH (Figures 4 and 14). The upper mudstone shows immature pedogene- sis with mottles of grayish-purple (5P 4/3) mudstone that may be mottled up to 50% by diffused light green- ish-gray (5G 8/1) redoximorphic iron depletion (Figure 22A). These mottle sizes are in the coarse range (5 to 20 Figure 16. Archival photographs showing the now-missing strata over the Quarry Sandstone. (A) View west with workers in the circle. (B) View east showing part of the bedding in the protective overburden (1938). Photographs by Albert Boyd, courtesy of Uintah County Library Regional History Center. 46 A River Runs Through It—The Quarry Sandstone and Adjacent Strata, Dinosaur National Monument, Utah Carpenter, K., and Taylor, L.H. Geology of the Intermountain West 2025 Volume 12 mm) of Schoeneberger et al. (2012). Other pedogene- sis includes white (N9) redoximorphic iron depletion delineating root traces (Figure 22B). Pedogenesis on the east side of the QEH includes weathered bands of pale-purple (5RP 7/2) below the crevasse splays. Un- weathered mudstone, as exposed in trenches, is dusky- purple (5RP 4/2) to grayish-purple (5P 4/2) with streaks of dusky-yellow (5Y 6/4) to very light gray (N8) redoxi- morphic iron depletions (Figure 22C). Pedogenic alter- ation is also seen on the southwestern part of the quarry wall in the QEH (Figures 22D and 22E). These diverse examples show that early protosol development is wide- spread in the mudstone facies. Paleosol carbonates are present and are discussed under Carbonates. One mineral identified in many of the thin sections (e.g., Appendix 1, Figure A2G) is the green mineral glauconite, or glaucony, as defined by Odin and Létolle (1978) and Odin and Matter (1981), where the propor- tion of smectitic and micaceous layers is undefined. It is present in both the mudstone and carbonate facies as green and brown grains, some of which are peloidal, suggesting a biogenic origin. Non-biogenic glaucony is most likely from pore-water chemistry altering existing smectite clay (Meunier, 2005), which is abundant in the Brushy Basin Member, rather than from a marine in- cursion with which it is often associated (Velde, 2014). Furquim et al. (2010) report that glauconite in the Pan- tanal wetland soils of Brazil is often interstratified with smectite, forming a mixed-layered mineral structure. Its formation is favored by alkaline, saline conditions with high potassium concentrations and reducing en- vironments that stabilize Fe3+. Glauconite crystallizes through neoformation from amorphous silica-rich ma- terials, or via transformation of smectite layers, with its formation varying based on seasonal microenviron- mental changes. The mineral was previously reported from the Brushy Basin Member by Craig et al. (1955) and Keller (1958, 1962), who referred to glaucony as “glauconitic mica.” A more detailed analysis of various mudstone beds is presented in Appendices 1 and 2. Tuff Facies Thin volcanic ash beds are present throughout the Brushy Basin Member, and Christiansen et al. (2015) reported 42 beds in Douglass Draw. These ashes are commonly shades of light gray or white (Figure 23A) and sometimes have a faint pinkish, purplish, or green- ish tint, as noted by Turner and Peterson (1991). Inter- nally, the ashes may be structureless, especially if diage- netically altered (Figure 23B), laminated, or composed of accretionary ash pellets (Figure 23C). Another exam- ple of ash pellets consists of matrix-supported, 1 to 10 mm ellipsoid-to-spherical pellets distributed random- ly throughout the tuff (Figure 23D). These pellets are composed of the same ash that encases them and they lack internal organization. They resemble the AP2 ac- cretionary pellets of Brown et al. (2012), although they lack internal structure, and some are significantly larg- er. The loss of internal structure might be diagenetic, but retention of the external shape suggests a primary structureless interior. These AP2 pellets occur in an ash bed immediately underlying sheet-like sandstone 1 adjacent to the Quar- ry Sandstone on the west side of the QEH (Figure 23E). This tuff is about 70 cm thick and slightly calcareous. Unlike many of the ashes in the study area, there is no siliciclastic detritus, and this clean ash must represent a primary deposit of a large volcanic eruption of an ash-rich plume into a standing body of water. The pre- dominant grain size of the tuff is 9 to 23 µm (fine- to medium-silt size), but a small percentage is 30 to 60 µm (medium- to coarse-silt size). Dispersed throughout Figure 17. The saddle eroded into muddy tabular sandstones seen in Figure 16. Abbreviations: c – calcrete; Jmb – Brushy Basin Member of the Morrison Formation; Kcm – Cedar Mountain Formation; ms – mudstone facies; QSs – Quarry Sandstone; tss – tabular muddy sandstone region; ms – mud- stone. Photograph by Earl Douglass (Carnegie Museum). 47 A River Runs Through It—The Quarry Sandstone and Adjacent Strata, Dinosaur National Monument, Utah Carpenter, K., and Taylor, L.H. Geology of the Intermountain West 2025 Volume 12 the ash are black minerals, primarily biotite. Zircons are abundant and well preserved (Figure 23F) and gave a weighted mean Th-corrected 206Pb/238U CA-ID-TIMS zircon age of 150.77 ± 0.39 Ma (K. Chamberlain, Uni- versity of Wyoming, personal communication, October 5, 2021). This ash provides the best age yet for the depo- sition of the Quarry Sandstone, and hence of its pre- served dinosaur fauna. Carbonate Facies Carbonates faicies includes carbonate beds or nod- ules in the sandy mudstone facies and as reworked clasts up to 15+ cm in maximum diameter in sandstone beds (Figure 24A). Special attention was given to nodules in mudstone because Dodson et al. (1980), Fiorillo (1994), and Retallack (1997) stated that some of those at Di- nosaur National Monument were pedogenic in origin Figure 18. (A) Sandstone (ss) grading rapidly to muddy sandstone (mss) to sandy mudstone (smdst) at QEH. (B) Rounded mud clast conglomerate exposed in the foundation trench that was excavated for the QEH. Scale in cm. (C) Irregular mud clast conglomerate exposed in the foundation trench. Scale in cm. (D) Muddy sheet sandstones (labeled 1, 2, 3) on the west side of the QEH. (E) Long bone (Stegosaurus femur) in a splay deposit on the west side of the QEH. 48 A River Runs Through It—The Quarry Sandstone and Adjacent Strata, Dinosaur National Monument, Utah Carpenter, K., and Taylor, L.H. Geology of the Intermountain West 2025 Volume 12 and indicative of well-drained or seasonally dry soils. In addition, Retallack (1997) used the depth to the calcic horizon in the predominately dusky red (10R 3/3), clay- ey, calcareous paleosols overlying the Quarry Sandstone to estimated rainfall as approximately 600 to 900 mm/yr. Nodules in mudstone are most commonly 0.75 to 2 cm in diameter and often have abrupt rather than dif- fuse boundaries with the encasing matrix (Figure 24B). Some of the oriented samples showing original struc- tures indicate an in-situ formation (e.g., Appendix 1, Figure A7A). Carbonate nodules typically erode from the mudstone (Figure 24C) and accumulate as a lag of fragments and whole nodules at the base of slopes. In contrast, limestone beds are thin (about 10 cm) and are best seen on the west side of the QEH (Figure 24D). This limestone tends to erode as large fragments (Figure 24E) and may be the source for the larger carbonate clasts in the sandstone beds. Both carbonate types are predom- inantly white (N8) or light greenish-gray (5G 8/1) to medium light-gray (N6) or even grayish-purple (5P 4/2). Most carbonates have a weathered surface of pale yellow-orange (10YR 8/6) to grayish-orange (10YR 7/4) caused by the oxidation of iron within the carbonate. Dodson et al. (1980) noted the carbonate horizons that they identified as calcretes in “red” or “purple” pa- leosols as well as in “gray-green” mudstone. Only nod- ules from the mudstone beds weathered “gray-green” on the east side of the QEH were examined by thin section. Some of these contained diplostracan branchiopods, ostracods, and rare charophytes. The fact that many of the diplostracan and ostracods are fragments or single valves, and some valves are at an angle relative to the bedding plane of oriented rock samples, suggests that these are mostly allochthonous fossil assemblages (e.g., Appendix 1, Figure A4). Diagenetic events observed in cross-sections and thin sections of the carbonates include septarian cracks infilled with calcite or quartz (Appendix 1, Figure A4A) and pedogenetic fracturing (Appendix 1, Figure A5A). Thin section analysis (Appendix 1) indicates that the allochems in the carbonate facies are dominated by ostracod fossil fragments and complete or nearly com- plete shells (e.g., Appendix 1, Figure A4C). This and the abundance of calcareous mudstone suggest that the limestones were deposited in relatively quiet water. Grains observed in the carbonate facies are predomi- nantly quartz, with rare grains of other minerals that suggest their igneous origin. Grains are mostly silt-sized or smaller and in such great abundance as to qualify the limestones as being silty. In contrast, Lawton (1976, p. 5) noted that many of the lenticular limestone beds in her samples were “clean,” presumably meaning free of siliciclastics. Lawton (1976) did note, however, that one limestone body contained “calcite-coated micro-mud- balls and irregular blocky clasts of silt and clay in calcite and chalcedony cement.” We also noted the presence of mud clasts in some of our samples. See Appendix 1 and Appendix 2 for additional photographs and descrip- tions. INTERPRETATION OF LITHOFACIES Isolated lenticular conglomeratic sandstone bodies are encased in sandy mudstone and we interpret them as fill of single-threaded channels. The sandy mudstone Figure 19. (A) Rapid coars- ening upwards of sand- stone 2. Scale in mm. (B) Lenticular bodies (distrib- utary channels) associated with the sheet sandstones of Figure 13D. Scale in dm. 49 A River Runs Through It—The Quarry Sandstone and Adjacent Strata, Dinosaur National Monument, Utah Carpenter, K., and Taylor, L.H. Geology of the Intermountain West 2025 Volume 12 are interpreted as proximal overbank deposits. Howev- er, the poor exposure due to the steep dip and in-situ weathering makes it difficult to determine whether lat- eral accretions are present or if the proximal overbank deposits are levee or crevasse splay deposits. The lowest thin tabular and wedge-shaped sandstone in the context of the muddy sandstone are interpreted as a succession of crevasse splay deposits preceding an avul- sion and redirection of the river that deposited the Quar- ry Sandstone. The different directions of wedging are ex- pected as the loci of the crevasse splay deposition shift with each event (Burns et al., 2019). Of the upper, now missing, bedded tabular sandstone bodies (Figure 16), little can be said because those beds cannot now be exam- ined. A proposal has been submitted to trench through the access road around to the west side of the QEH to provide this important information. Several lines of evidence taken together, rather than any single feature, indicate that the Quarry Sandstone consists of stacked braided (multichannel) fluvial de- posits: (1) the sandstone bodies are sheetlike, having high width-to-thickness ratios characteristic of multi- thread rivers (Labourdette, 2011); (2) vertical accretion of sandstone sheets separated by gently undulating ero- sional surfaces represents stacked compound bars simi- lar to those of the South Saskatchewan River (Sambrook Figure 20. (A) Abrupt facies change from a lower clay-rich mudstone to an upper sandy and silty mudstone at Dinosaur Peak, west side of the QEH. Also present are three limestone beds (labeled 1, 2, 3). Abbreviation: s3 correlates with sandstone 3 on the east side (see Figure 15). Scale in decimeters. (B) Historic photograph (around 1958) showing lenses of sandstone and carbonate in the unweathered gray mudstone. Compare with (A). Photograph courtesy of National Park Service. (C) Pedogenic mottling (protosol) with colors saturated to bring out differences. (D) Detail of blocky sandy and silty mudstone. Scales in B through D in cm. 50 A River Runs Through It—The Quarry Sandstone and Adjacent Strata, Dinosaur National Monument, Utah Carpenter, K., and Taylor, L.H. Geology of the Intermountain West 2025 Volume 12 Smith et al., 2006); (3) the coarse sand to cobble grain- size fraction ranges up to 1 cm in diameter (rarely great- er than 10 cm), excluding the transported greater than 160-cm dinosaur limb bones, but the sand grains typ- ically range from 0.5 to 1 mm in diameter with D50 1 mm (Carpenter, 2013); (4) the generally clean sands in- dicate turbulent flow or bed reworking that winnowed out clay particles; (5) the presence of pockets of fine- grain slack-water deposits in otherwise coarse-grained sandstone, which are mostly associated with troughs (Lynds and Hajek, 2006); (6) the abrupt transition from coarse-grain sandstone to fine-grain sandstone and thin clay drapes over undulating erosional surfaces in- dicates a rapid drop in transport energy associated with flashy discharge; (7) the presence of three-dimensional bars (mega-bedforms); and (8) the lack of lateral accre- tion deposits, which are more typical of sinuous sin- gle-threaded rivers. Trough cross-stratification and pla- nar stratification are not included as evidence because both also are present in single-channel sinuous river deposits and crevasse splays (Brierley, 1996; Bridge, 2003). These multiple lines of evidence align with mod- ern alalogues of the complex subsurface architecture and history of sandy braided river deposits revealed by ground-penetrating radar of the Saskatschewan River, deposits in Canada (Sambrook Smith et al., 2006). The correlation between grain size/channel depth (grain size D50 = 1 mm; depth = approximately 1 m for the Quarry Sandstone) and slope (Paola and Mohring, 1996; Friend and Dade, 2005) suggests that the river depositing the Quarry Sandstone had a paleoslope of 10-3 to 10-4 with bedload dominating. This projected paleoslope is close to the 1.1 x 10-3 estimated for the Morrison depositional environment by Trampush et al. (2013), whereas Lawton (1976) concluded the chan- nel gradient at the quarry as 3.8 x 10-4. The paleoslope methods of Lynds et al. (2014) were not used because these were developed for sandy suspended-load rivers with maximum grain size of less than 0.5 mm and D50 is significantly less; these values are significantly less than the 1 mm D50 of the Quarry Sandstone. Peak discharge most likely occurred during seasonal rains, resulting in overbank flooding and floodplain in- undation. Paleocurrent data for the Quarry Sandstone Figure 21. (A) Detail of smectitic lower mudstone (DINO 48397). (B) Polished surface of (A) showing extensive bioturba- tion and possible rhizoliths (labeled r). Scale in mm. 51 A River Runs Through It—The Quarry Sandstone and Adjacent Strata, Dinosaur National Monument, Utah Carpenter, K., and Taylor, L.H. Geology of the Intermountain West 2025 Volume 12 from sedimentary structures (Figure 25A), unionid clam long-axes (Figure 25B), and dinosaur limb bones (Figure 25C) indicate the overall flow was toward the southeast. The greater vector spread of the limb bones is because some bones tend to roll perpendicular to the current, and some bones are trapped against the upstream side of bone piles or jams (Carpenter, 2013). Perhaps the best paleocurrent indicators are the long whip-like tails of diplodocid sauropods (Figures 25D and 25E). These rope-like structures offered little resis- tance to water flow, as has been demonstrated experi- mentally in a water flume (Carpenter, 2020b). Few of the channel sandstone bodies in the Quar- ry Sandstone have distinctive lateral margins or show an abrupt change in lithology or grain size that could represent the incised channel margin or bank. Most of the sandstone bodies show diffuse margins marked by a rapid increase in clay content, coincidental with a change from sandstone to muddy sandstone (Figure 18A) to sandy mudstone in which grains up to 2 mm may be suspended. This lack of well-defined or absent margins implies a fluvial system of frequent spillage sedimentation building the confining banks (Lewin and Ashworth, 2014; Lewin et al., 2017). Such systems are typical for non-montane braided or multithreaded river systems with their complex of active and inactive channels on the braid plain. These inactive channels may convey water at high river stage, resulting in pock- ets of finer sand sediments in otherwise coarse-grained deposits. On outcrop, the transition from well-cemented, ero- sion-resistant channel sandstone to more easily eroded muddier sandstone typically takes place over a span of a few meters. This transition zone is not uniform, as local variation in clay content and cementation is reflected in the differential erodibility of the sandstone, such as seen on the west side of the QEH both within the build- ing and adjacent to it (Figure 18B). These transitional sandstone bodies typically are fine-grained distally and are interpreted to be the proximal overbank facies, pre- dominantly spillage sedimentation of levees and cre- vasse splay deposits (e.g., Cazanacli and Smith, 1998; Figure 22. Diverse examples of pedogenesis in mudstone beds of the study area. (A) Light-colored mottles in reddish mud- stone (color enhanced). (B) Rhizoliths in gray calcareous mudstone. (C) Rhizoliths and light-colored mottles in gray to brown mudstone (color enhanced). (D) Light-colored mottles in purple mudstone on the west end of the QEH (color en- hanced). (E) Light gray and dark gray mottles in mudstone on the west end of the QEH. Scales in cm. 52 A River Runs Through It—The Quarry Sandstone and Adjacent Strata, Dinosaur National Monument, Utah Carpenter, K., and Taylor, L.H. Geology of the Intermountain West 2025 Volume 12 Hudson, 2005; Alexander and Fielding, 2006; Lewin et al., 2017). The coarseness of these proximal overbank deposits is most commonly associated with fluvial sys- tems having highly variable discharge (Alexander and Fielding, 2006). Levee and crevasse splay deposits share similar cri- teria (e.g., sharp bases, distal thinning, and fining), and distinguishing them is made more difficult by the lim- ited exposure of the Quarry Sandstone on the steeply dipping cross sections. The radiating paleocurrent pat- tern of crevasse splays, which is not known to occur in levees, has been identified on the west side of the QEH where two sandstone beds merge in a small area corre- sponding to a breakout point in a levee (Figure 18D). The main distributary channels of these splays are seen in cross section (Figure 19B) and prograding into the flood basin, evident by the coarsening upwards (Figure 19A). Although levees tend to be well-drained because of their elevation above the bottomland, the absence of mature paleosols in any of the proximal sediments implies high rates of vertical accretion. Dinosaur bones occur in the transitional sandstone beds, but their siz- es decrease away from the channel, corresponding to a decrease in flow velocity. The burial of these bones was probably due to downstream progradation of the levees during floods (Johnston et al., 2019). The finer-grained mudstone and bedded limestone are interpreted to be floodplain and lacustrine deposits distal to the levee and crevasse splay deposits, hence rep- resenting the distal overbank facies. The floodplain de- posits are drab gray (N6 to N3) calcic Gleysols with some carbonate nodules and some lacustrine limestone, as in- dicated by their microfossils. Many of the diplostracans in the limestone consist of only one valve of the bivalved carapace, which furthermore may be broken, indicating turbulent fluvial transport across the floodplain prior to deposition in topographic lows (i.e., areas of negative re- lief). Retallack (1997) referred to these gray mudstone beds as periodically waterlogged paleosols. Figure 23. (A) Thin bed of volcanic ash in Douglass Draw. (B) Structureless diagenetically altered silicified ash from the right side of (A), DINO 48399. (C) Oriented compressed pellets of accretionary ash from the left side of (A), DINO 48400. (D) Matrix-supported Type AP2 accretionary pellets from (E). (E) Ash immediately below sandstone 1 of Figure 18D. (F) Exam- ple of pristine zircons from (E). Courtesy of K. Chamberlain, University of Wyoming. 53 A River Runs Through It—The Quarry Sandstone and Adjacent Strata, Dinosaur National Monument, Utah Carpenter, K., and Taylor, L.H. Geology of the Intermountain West 2025 Volume 12 In contrast, the absence of clay or siliciclastic grains in the Quarry ash indicates airfall sedimentation into a floodplain pond rather than fluvial transport of the ash into a topographic low. Brown et al. (2012) noted that historic eruptions reaching the tropopause typically have a distal region of increased fallout composed of aggre- gates of ash. They identified several, mostly hydrometeor mechanisms for accretionary formation. The size of the largest pellets in the QVC tuff suggests a late-stage for- mation most likely involving water droplets. The distal mass deposition maxima of modern eruptions reaching the tropopause may be hundreds of kilometers from the volcano. For example, the centroid for the distal deposi- tion maxima for the 1980 Mount Saint Helens eruption was 500 km downwind (Brown et al., 2012). For the ash at Dinosaur National Monument, the source is believed to have been the Mohave volcanic center about 680 km to the southwest (Hart et al., 2005; Christiansen et al., 2015). DEPOSITION ENVIRONMENT OF THE QUARRY SANDSTONE Accommodation The unusually wide Quarry Sandstone within the Brushy Basin Member has been previously noted by several researchers (Bilbey et al., 1974; Lawton, 1977; Turner and Peterson, 1992a; Carpenter, 2013; Brezins- ki and Kollar, 2018). The average paleocurrent trend is roughly perpendicular to the 1.5-km-wide exposure of these stacked and amalgamated sandstone beds sug- gesting the sandstone represents a broad fluvial system with multiple channels. Recent studies of similar wide stacked and amalgamated sandstone beds emphasize the critical roles of both accommodation and sediment supply (e.g., Labourdette, 2011; Sharma et al., 2023). Ac- commodation, closely tied to sediment accumulation, refers to the “thickness” of sediment deposited over time (Muto and Steel, 2000). Sediment supply refers to Figure 24. Carbonates. (A) Large reworked carbonate in Quarry Sandstone near the QEH. Scale in cm. (B) Nodule in situ at the tip of a pen, with an abrupt boundary with mudstone on the east side of the QEH. Scale in cm. (C) Nodules eroding in situ from mudstone, showing their relative density. Hammer for scale. (D) Edge view of multiple limestone beds. The upper right bed correlates with (E). Jacob staff with alidade holder (1.25 m) for scale. These beds are also seen in Figure 20A. (E) Eroding surface of limestone bed at Dinosaur Peak, west side of the QEH. Aluminum clipboard for scale. 54 A River Runs Through It—The Quarry Sandstone and Adjacent Strata, Dinosaur National Monument, Utah Carpenter, K., and Taylor, L.H. Geology of the Intermountain West 2025 Volume 12 the “volume” of sediment deposited within a given peri- od. Accommodation is primarily controlled by tectonic processes such as basin uplift or subsidence, along with changes in eustatic or local base level. Sediment supply is influenced by erosion rates associated with uplift and climate in the catchment area (Allen, 2017; Caracciolo et al., 2020). Sediment transfer through a sediment routing sys- tem from its origin to its final deposition site is gov- erned by both allogenic and autogenic processes. These influences are evident in the variations observed in sedimentary successions, including changes in chan- nel distribution, channel density, and the width of river channels and channel belt deposits. The resulting depo- sition continuum can range from low-density narrow shoe-string channels encased in finer overbank depos- its, reflecting high accommodation-to-sediment supply ratios (A/S), to high-density interconnected tabular channels indicative of low A/S ratios (Bridge and Leed- er, 1979; Huerta et al., 2011). These A/S ratios remain consistent even when accounting for variables such as compaction (Bridge and Mackey, 1993). Several studies illustrate the role of basin subsidence as a major factor influencing the A/S ratio. For example, Labourdette (2011) in an in-depth study of the Eocene Olson Member of the Escanilla Formation in the Ain- sa Basin of northern Spain, reported that variations in basin subsidence during the Eocene were the primary drivers of accommodation space for sediment deposi- tion. During periods of slow subsidence, low accommo- dation caused braided channels to laterally stack, form- ing wide multichannel belts. Conversely, during periods of faster subsidence, high accommodation resulted in narrower and thicker single-threaded channels. In the Morrison Formation of the Colorado Plateau, variations in accommodation space have been linked to shifts in fluvial system dynamics and sedimentary facies distributions. Heller et al. (2015) noted an inverse rela- tionship between channel-belt stacking and floodplain aggradation in the Upper Jurassic Morrison Formation of Utah, USA, linking this to basin subsidence and ac- commodation. They associated the density of channel stacking with avulsion frequency, which is coupled with the sedimentation rate in the channel belt (Heller and Paola, 1996; Heller et al., 2015). Whereas subsidence fluctuations in a basin are a major method of altering accommodation space, changes can also occur during the inversion of an in- tracratonic rift. This possibility has not been previously considered for the Morrison Formation, but we explore it here to account for the unusual Quarry Sandstone, given its proximity to the inverted Uinta rift, which now forms the core of the Uinta Mountains (Dehler and Sprinkel, 2005). The Uinta Mountains, a product Figure 25. Quarry Sandstone pa- leocurrent based on (A) sedi- mentary structures; (B) long axis of unionid bivalves; (C) dinosaur limb bones. Arrow at margins in- dicates the axis of the mean. Quar- ry excavation maps showing the effects of flowing water on long whip-tailed sauropods recovered from the Quarry Sandstone; (D) Apatosaurus from Gilmore (1936); (E) Diplodocus, unpublished from Earl Douglass (Carnegie Muse- um). Data for (A) and (B) provid- ed by Fred Peterson, U.S. Geolog- ical Survey. 55 A River Runs Through It—The Quarry Sandstone and Adjacent Strata, Dinosaur National Monument, Utah Carpenter, K., and Taylor, L.H. Geology of the Intermountain West 2025 Volume 12 of the Late Cretaceous Laramide orogeny, have a core composed of the Neoproterozoic-aged Uinta Mountain Group, which was deposited in mixed marine, delta- ic, and braided river environments within a failed rift (Dehler and Sprinkel, 2005). This intracratonic rift rep- resents an early phase in the breakup of the Rodinia supercontinent along the western margin of Laurentia. The rift was bounded by inward-dipping normal faults produced by crustal extension on the north and south. Modeling suggests that during later contraction these faults were reactivated as reverse faults, and addition- al faults were created, including low-angle thrust faults (Pinto et al., 2010). The Uinta Mountain rift basin ex- perienced several contractional events between the late Neoproterozoic and Late Cretaceous (Hansen, 1986a, 1986b; Stone, 1993; Sprinkel, 2014), as evidenced by angular unconformities in formations around the Uinta Mountains (Williams, 1953; Sprinkel, 2014). Contrac- tion during the Cenozoic led to the formation of nu- merous synclines and anticlines flanking the eastern Uinta Mountains (Hansen, 1986a, 1986b). One of these, the Split Mountain anticline, formed between the As- phalt Ridge thrust fault to the south and the Island Park normal fault to the north, represents a reactivation of an older anticline developed during the Late Jurassic, as discussed below. The compressional forces acting against the Uinta rift were oblique, directed toward the northeast (John- ston and Yin, 2001; Ashby et al., 2005). These oblique forces likely resulted from the movement of the Colo- rado Plateau driven by the Farallon subduction (Sassi et al., 2012). Paleomagnetic data indicate that the Colora- do Plateau has moved 160 km ± 36 km since the Triassic (Erskine, 2001), accompanied by a clockwise rotation of approximately 9° during the Jurassic relative to a Euler pole on the North American continent (Steiner, 2003). This movement was probably episodic, as suggested by the different paleopole positions of the lower and upper Morrison Formation (Steiner, 2003) and the episodic growth of the Mexico-Alaska megashear zone (Ander- son, 2015). Modeling suggests that oblique compression of one block relative to another can produce transpressional uplift or an anticline (Dewey et al., 1998). Bally (1984) previously predicted an asymmetrical “petit inversion” anticline adjacent to the bounding fault of an inverted rift (Figure 26A). Additionally, in Bally’s (1984) mod- el, syn-sedimentation would prevent the anticline from breaching the surface. Although not explicitly stated, Bally’s figure shows a reduction in accommodation space above the anticline, which would influence sed- iment deposition by any fluvial system flowing over it. Similar situations were reported by Peterson (1980, 1984) from the Henry Mountains basin, Utah (see DIS- CUSSION). We propose that an example of “petit inversion” of Bally (1984) as a proto-Split Mountain anticline like- ly influenced the deposition of the Quarry Sandstone, Figure 26. (A) Small anticline due to a “petit inversion” of a rift margin as predicted by Bailey (1984, Figure 4). (B) Transpres- sive rift inversion caused by the Colorado Plateau during the latter part of the Late Jurassic. The effects on local sedimenta- tion by the proto-Split Mountain anticline are visible in the accommodation space. T-1 represents pre-uplift with no change in accommodation space; unit thickness is uniform. Uplift begins between T-1 and T-2, starting to reduce accommodation space over the anticline; peak reduction by T-2. 56 A River Runs Through It—The Quarry Sandstone and Adjacent Strata, Dinosaur National Monument, Utah Carpenter, K., and Taylor, L.H. Geology of the Intermountain West 2025 Volume 12 based on the thinning of the Brushy Basin Member (Fig- ure 26A) along a north-south transect (Figure 27B). In contrast, a thickening in the underlying Middle Jurassic Curtis Formation suggests that the “petit inversion” had not yet occurred at that time (Figure 27C). The thick- ness of the Morrison Formation members indicates that the compression event and resulting transpressional uplift began after the deposition of the Tidwell Member sediments, making the event younger than the 156.84 ± 0.59 Ma 40Ar/39Ar date from the Tidwell Member at Rainbow Draw (locality 2 on Figure 27B; Trujillo and Kowallis, 2015). It is likely that the transpressional uplift began during the deposition of the Brushy Basin Mem- ber, resulting in the Morrison Formation being 40 to 45 m thinner near the uplift than it is to the north or south. The location of the proto-Split Mountain anticline near the southern boundary fault of the Uinta rift aligns with Bally’s (1984) prediction, as the peak compression force on the inversion block dissipates from peak pressure near the boundary fault. Additionally, this asymmet- rical compression loading results in an asymmetrical anticline, with the steeper side facing the compression loading. The proto-Split Mountain anticline contributed to the shifting of multiple active and semi-active channels. The rapid reduction in accommodation is evidenced by the abrupt transition from isolated lenticular sand- stone bodies to laterally interconnected braided river channel belt deposits of the Quarry Sandstone (Fig- ure 6). This connection results from channel avulsions, spillage, overlapping of channel deposits, and spillage cannibalism due to the lateral mobility of the channels (Labourdette, 2011; Colombera and Mountney, 2021). The frequent avulsions were likely the result of aggrada- tion of the channels, the availability of steeper alterna- tive flow paths in the adjacent floodplains, and in some cases to the presence of large dinosaur bone accumula- tions. Bone and carcasses probably had the same effect as wood in fluvial systems by increasing channel rough- ness, altering flow hydraulics, and decreasing sediment transport (Cadol and Wohl, 2011; Spreitzer et al., 2012). The accumulation of bones and carcasses forming large jams (Figure 28) in the channels may have also contrib- uted to avulsions by obstructing the channels, directing flow toward the unstable margins much the same way as log jams can trigger avulsions (Phillips, 2012). Brum- mer and Montgomery (2006) noted that the presence of boulders covering 20% of the riverbed was enough to cause channel widening during floods. Log jams can initiate multi-channel patterns by diverting flow to a secondary path (Sear et al., 2010; Cadol and Wohl, 2011), and carcasses (see Figure 1 in Carpenter, 2020a) and bone jams have been shown to have that effect (Carpenter, 2020b). Channel obstacles also act as sediment traps by in- creasing frictional flow resistance and causing turbulent eddies that reduce flow velocity and sediment transport competence (Carpenter, 2020a). Thus, bones behave much like boulders on the riverbed by constituting a major roughness element imparting form drag on flow (Ferguson, 2007). The result is the deposition of sedi- ment in the channel (Spreitzer et al., 2021; Chen et al., in press). This deposition is greater during floods, where the added suspended mass and increased viscosity en- hance the logjam's ability to slow down the flow (Chen et al., in press); bone jams would have the same effect. The sudden change in fluvial styles near the QEH began around 150.77 ± 0.39 Ma, as indicated by volca- nic ash immediately below the Quarry Sandstone and represented by the T2 timeline in Figure 26B. The du- ration of the anticline’s subsurface uplift and the time until accommodation space was restored to pre-uplift conditions remain unknown, but it likely took thou- sands of years based on the local thickness of the Brushy Basin Member and its depositional duration of less than 2 million years (Christiansen et al., 2015). The Quarry Sandstone shows little confined flow due to avulsions and overlapping proximal overbank flow (levees and splays) across the floodplain until channels were re-established elsewhere. Mud pebble clasts from bank or levee collapse, matrix-supported coarse grains, and weakly developed paleosol mottling are common. It lacks the lateral accretion or other fea- tures characteristic of meandering rivers, such as those identified below. A similar situation of lateral mobility leading to the formation of a new braid plain can be observed in the gravelly braided Blaeberry River, British Coloumbia, Canada (Figure 29). In this case, a crevasse splay pre- ceded the avulsion event, indicating bank instability, but 57 A River Runs Through It—The Quarry Sandstone and Adjacent Strata, Dinosaur National Monument, Utah Carpenter, K., and Taylor, L.H. Geology of the Intermountain West 2025 Volume 12 the avulsion occurred farther upstream, creating a new braid plain parallel to the old one. Whether an erosive breach becomes a crevasse splay or leads to an avulsion is determined by the balance between erosion and depo- sition processes, influenced by factors such as floodplain erodibility, vegetation, and water surface slope (Nienhu- is et al., 2018). A wide zone of interconnectivity is visible in the vicinity of the avulsion, highlighting the impor- tance of spillage, especially crevasse splays, in connectiv- ity between channels (Columbera and Mountney, 2021). Figure 27. Rift inversion impact on accommodation space is observed by (A) thinning of the Morrison Formation over the proto-Split Mountain anticline. Redwater Member, Stump Formation (Jsr); Tidwell Member, Morrison Formation (Jmt); Salt Wash Member, Morrison Formation (Jms); Brushy Basin Member, Morrison Formation (Jmbb); Quarry Sandstone (QSS). (B) Map of northern Utah showing the boundaries of the Uinta rift, location of measured sections, and the axis of the Split Mountain anticline today. (C) Pre-rift inversion influence on the deposition of the underlying Curtis Member, Stump Formation (Jsc); Entrada Sandstone (Je). 58 A River Runs Through It—The Quarry Sandstone and Adjacent Strata, Dinosaur National Monument, Utah Carpenter, K., and Taylor, L.H. Geology of the Intermountain West 2025 Volume 12 Fi gu re 2 8. B on e cl us te rs o r “b on e ja m s,” a na lo go us to lo g ja m s, un do ub te dl y im pa ct ed w at er fl ow a nd c au se d se di m en t d ep os iti on . ( A ) B on e ja m s su rr ou nd ed b y ba rr en o r n ea rly b ar re n ro ck . ( B) E xa m pl e of a sm al l b on e ja m . ( C ) D ow ns tr ea m v ie w o f a b on e ja m . 59 A River Runs Through It—The Quarry Sandstone and Adjacent Strata, Dinosaur National Monument, Utah Carpenter, K., and Taylor, L.H. Geology of the Intermountain West 2025 Volume 12 To test the hypothesis that the Quarry Sandstone resulted from a loss of accommodation space due to the activity of a proto-Split Mountain anticline, we ex- amined sandstone beds along the western periphery of Split Mountain, which provides a nearly continuous exposure of the Morrison Formation from the QEH (Figure 30A). Our objective was to identify a sandstone body located upstream of the proto-Split Mountain an- ticline. The search criteria included stratigraphic place- ment near the middle of the Brushy Basin Member, a similar conglomeratic salt-and-pepper lithology, and the presence of dinosaur bones with comparable pres- ervation. Although several sandstone bodies were iden- tified, only two met all these criteria. One such sandstone body is 6.9 km west of the QEH (Figures 30B and 30C), whereas the other is 8.6 km northwest of the QEH (Figures 30D and 30E). The west- ern sandstone represents an infilled thalweg on the cut bank side of a single-threaded river, with a paleocur- rent direction of 182° as determined from the axis of the thalweg. This sandstone body measures approximately 70 m wide perpendicular to its axis. The northwestern sandstone, on the other hand, is a cross section of a sin- gle-threaded river deposit featuring accretionary de- posits on the eastern side and the thickest sandstone on the west. The paleocurrent direction for this sandstone body is around 145°. The entire sandstone body, includ- ing the accretionary deposits, is 232 m wide, with the main body forming a resistant ridge measuring about 157 m in width. The northwestern sandstone body exhibits pa- leocurrents that suggest it served as the upstream seg- ment for both the western sandstone and the Quarry Sandstone. It may have been the source of sediment for both at different times. As the upstream segment to the Quarry Sandstone, a sinuous single-threaded river like- ly transitioned into a multithreaded system as it crossed the proto-Split Mountain anticline and then possibly Figure 29. Relocation of a braided river channel over time as a model for the Quarry Sandstone, Blaeberry River, British Co- lumbia (51.4264°N., -117.0709°W.). (A) Pre-avulsion with crevasse splay sediment (arrow). Image date: 2004. (B) Pre-avul- sion with recolonization of the crevasse splay surface by vegetation (arrow and similar brown patterns). Image date: June 25, 2015. (C) Post-avulsion in spring 2019, showing the abandonment of the previous braid plain. Note the extensive reworking by shallow flow of the previous braid plain from the spring flood prior to complete abandonment. Image date: September 4, 2019. (D) Fully established new braid plain. A wide region of interconnectivity between the two braid plains is marked by a red box. Image date: August 2022. Images: (A) through (C) Google Earth; (D) Bing Maps. 60 A River Runs Through It—The Quarry Sandstone and Adjacent Strata, Dinosaur National Monument, Utah Carpenter, K., and Taylor, L.H. Geology of the Intermountain West 2025 Volume 12 Figure 30. (A) Distribution of the Morrison Formation around the western end of Split Mountain. Two sandstone bodies match the lithology of the Quarry Sandstone. (B) Outcrop of the western sandstone with (C) a sauropod vertebra (scale in cm). (D) Outcrop of the northwestern sandstone with (E) a sauropod limb fragment (hammer head length approximately 17 cm). Abbreviation: QEH – Quarry Exhibit Hall. Base map from Topozone. 61 A River Runs Through It—The Quarry Sandstone and Adjacent Strata, Dinosaur National Monument, Utah Carpenter, K., and Taylor, L.H. Geology of the Intermountain West 2025 Volume 12 reverted to a single-threaded river afterward. Such tri- partite transitions are observed in modern rivers (e.g., Figure 31). Depositional Model A hypothetical paleoenvironmental cross section from channel to floodplain is presented in Figure 32 (see also Carpenter, 2023). The vegetation is mostly based on palynomorphs recovered by F. Peterson (U.S. Geological Survey) west of the QEH along Camp Draw (Turner and Peterson, 1991) and reported by Litwin et al. (1998). Megafloral specimens include the ginkgo- phyte, Czekanowskia, from a fine-grained, horizontally laminated sandstone interbedded in the Ridge Sand- stone, and a cycadeoid log fragment eroded from the Ridge Sandstone. These taxa plus other non-vertebrate fossils are given in Table 1. We interpret the Quarry Sandstone channel facies as a braided river whose deposits are not well differ- entiated laterally from the proximal overbank facies, reflecting the rapid deceleration of overbank flow and deposition of coarse-grained sediment. Flume work suggests that wide braided rivers that are not laterally constrained—i.e., have minimal bank cohesion, pro- duce a stable channel when width is about 24 times depth (Warburton, 1996). This is apparently controlled by grain size (Paola and Mohrig, 1996) and the devel- opment of natural levees thus lead to self-containment (Cazanacli and Smith, 1998). We propose a similar Figure 31. Example of a sinuous, single-threaded river tran- sitioning to a multithreaded river and back to a sinuous, sin- gle-threaded river. Flow is toward the left. Blaeberry River, British Columbia (51.4265°N., -117.0507°W.). Imagery date: October 11, 2021, Google Earth. Kingdom Plantae Division Charophyta Family Characeae Aclistochara bransoni Aclistochara latisulcata Alistochara madleri Aclistochara miniscula? Aclistochara obovata Latochara /atitruncata Latochara sp. Peckisphaera verticillata Porochara arguta Porochara kimmeridgensis Family Clavatoraceae Echinochara sp. Division Polypodiophyta Family Equisetaceae Equisetum sp. Division Pteriodophyta Family Umkomasiaceae Pteruchipollenites microsaccus* Family Osmundaceae Todisporites minor * Division unknown Bennettitales (family and genus unknown) Division Pinophyta Family Araucariaceae Callialasporites trilobatus * Callialasporites. cf C. rugularus * Family Podocarpaceae Microcachrydites antarcticus * Parvisaccites sp. * Rugubivesiculites sp. * Division Ginkgophyta Family Czekanowskiaceae Czekanowskia sp. Kingdom Animalae Class Bivalvia Family Unionidae Vetulonaia sp. genus unidentified Class Ostracoda Family Cyprididae Candona sp. Family Limnocytheridae Bisulcocypris pahasapensis Helmdachia petersoni Family incertae sedis Cetacella sp. Class Branchiopoda Family Cyzicidae Lioestheria sp. Table 1. Non-vertebrate fossils from the study area (see Greg- son et al., 2024, Table 1 for vertebrates). The plants were used to reconstruct the habitat shown in Figure 32. Palynoflora marked with * from Ash (1994); Litwin et al. (1998). Inver- tebrates from Schudack et al. (1998), Schudack unpublished (taxa updated by Benjamin Sames, personal communica- tions, April 11, 2022), Good (2004), Lucas and Kirkland (1998). 62 A River Runs Through It—The Quarry Sandstone and Adjacent Strata, Dinosaur National Monument, Utah Carpenter, K., and Taylor, L.H. Geology of the Intermountain West 2025 Volume 12 mechanism was in operation with the Quarry Sand- stone fluvial system. The absence of interbedded paleosols in the prox- imal overbank suggests that flood disturbances and sediment deposition were frequent enough to maintain a continuously disturbed habitat colonized by polypo- diopsid pteridophytes (ferns and tree ferns), known as pioneer species today (Walker and Sharpe, 2010). Slower-growing tree seedlings attempting to establish themselves were likely smothered by sediment, along with older established trees, as the crevasse splays pro- graded, as indicated by the presence of dead trees. The coarseness and white color of the sediments suggest well-drained, oxidizing soil with limited organic car- bon buildup. Overbank facies sediments become fin- er-grained distally, with immature paleosols and rhizo- liths in the B-horizon indicating sedimentation hiatuses in the range of decades rather than hundreds of years (Kraus, 1987; Burns et al., 2019). The absence of large rhizoliths of tree roots in the Morrison Formation has long been a mystery. Trees are known to have been present in the vicinity of the Quar- ry Sandstone, as evidenced by a log on the quarry face (Figure 33A). The absence of large tree tap-roots in pa- leosols of this study may be explained by conifers gen- erally having shallow, horizontal roots (Figure 33B), as a result of which trees commonly topple, exposing their shallow roots (Figure 33C). Decomposition of the roots by insects, especially termites known from the Mor- rison (Hasiotis, 2004), and saprophagic activity could have removed the evidence of large, horizontal roots over time (see Gee, 2023). The vegetation in this area consisted of a mixed riverine conifer-dominated forest of two species of araucariacean, three species of podocarpacean, and the ginkgophyte Czekanowskia, with an understory of shade-tolerant ferns. Today, such trees inhabit moist, well-drained soils in humid climates. Cycadeoids were also present, as evidenced by a section of log from the channel facies. In the flood basin, there were small water bodies that primarily received water sporadically from over- land flow (crevasse splay drainage, floods, rain). Lon- ger-lasting water bodies probably also received ground- water seepage flowing through the coarser sediments of crevasse splays. Fragmentary or single microcrusta- cean valves, some angled relative to the bedding plane of oriented rock samples, suggest the presence of some allochthonous assemblages. Additionally, branchiopod diversity is very low in bulk samples of matrix collected by F. Peterson (Turner and Peterson, 1991) along a tran- sect west of the QEH having only one or two species, suggesting a similarity to modern stressed ecosystems. The brecciation of some lacustrine carbonates indicates pedogenetic episodes in the flood basin. DISCUSSION Our analysis of the Quarry Sandstone and its sur- rounding strata provides a foundation for reassessing Figure 32. Reconstructed cross section from channel to floodplain, with inferred distribution of vegetation. No scale implied. 63 A River Runs Through It—The Quarry Sandstone and Adjacent Strata, Dinosaur National Monument, Utah Carpenter, K., and Taylor, L.H. Geology of the Intermountain West 2025 Volume 12 prior studies of the sedimentology of the Morrison For- mation at Dinosaur National Monument. Consistent with earlier research, we interpret the Quarry Sandstone as the product of braided river systems accompanied by finer-grained overbank deposits (e.g., Lawton, 1977; Turner and Peterson, 1992a; Carpenter, 2013). Tradi- tional interpretations of braided rivers often regarded associated overbank or vertical accretion deposits as volumetrically insignificant (e.g., Miall, 1977; Cant and Walker, 1978; Walker and Cant, 1984). This perspective emerged primarily from studies of valley-confined or in- cised braided rivers, in which frequent channel shifts re- worked overbank deposits, leaving behind only erosional remnants (Cant and Walker, 1978; Bridge, 2003, p. 157). However, such interpretations are inconsistent with the stratigraphic record, which often reveals extensive overbank deposits associated with braided river sys- tems. Examples include the Atcotas Formation of Spain (Arche and Lopez-Gomez, 1999), the Cutler Formation of New Mexico (Eberth and Miall, 1991), the Escanil- la Formation of Spain (Bentham et al., 1993), and the Salt Wash Member of the Morrison Formation on the Colorado Plateau (Robinson and McCabe, 1998). The volume of finer-grained floodplain deposits in braid- ed river systems correlates strongly with rates of basin aggradation (e.g., Bentham et al., 1993; Robinson and McCabe, 1998; Labourdette, 2011). Consequently, the relative thickness of vertical accretion deposits is no longer considered a primary criterion for distinguish- ing between meandering and braided river deposits (e.g., Miall, 2014). Additionally, proximity to orogenic mountains fronts does not necessarily dictate the development of braided river systems, as demonstrated by the 1899 topographical map of the Platte River near Columbus, Nebraska (U.S. Geological Survey, 1899). This map il- lustrates that, prior to channelization and dam con- struction, the Platte River was braided nearly 700 km downstream from the Hartville uplift in eastern Wy- oming. This was also demonstrated by Holbrook and Allen (2020), who noted that the lower reaches of the Missouri River were braided prior to damming and channelization. Finally, Bridge at al. (1998) described the braided part of the Calamus River, which originates in the Sand Hills of western and central Nebraska, not from any orogenic front. These and other studies sup- port the prevalence of braided rivers, which are now recognized as being as common as meandering rivers globally (Miall, 2014, p. 39). In a significant departure from the consensus that the Quarry Sandstone represents channel deposits, Brezinski and Kollar (2018) interpreted the Quarry Sandstone as a crevasse splay complex, which consists of multiple genetically related splay and crevasse-chan- nel fill elements formed in an interfluve wetland or lake. They based their analogy on a distributary channel of the clay and silt Mississippi River Delta (Figure 34A), as described and illustrated by Coleman and Prior (1982). Brezinski and Kollar (2018) identified the Quarry Sand- stone as being composed of numerous laterally contin- uous and upward-coarsening sandstone bodies, which they interpreted as distributary mouth bars within cre- Figure 33. (A) Fossil log on the quarry face in the QEH (approximately 3 m in length). (B) Conifer showing laterally directed roots that provide a broad base for support. (C) Root mass of a toppled conifer showing the absence of major taproots. 64 A River Runs Through It—The Quarry Sandstone and Adjacent Strata, Dinosaur National Monument, Utah Carpenter, K., and Taylor, L.H. Geology of the Intermountain West 2025 Volume 12 vasse splays. These bars were cut by trough cross-bed- ded and upward-fining sandstone lenses, which they identified as distributary channels. They proposed that the 130-m-wide quarry bed was formed within one of these channels. There is a moderate to strong correlation between crevasse splay width and parent channel width (Mil- lard et al., 2017; Columbera and Mountney, 2021; Rah- man et al., 2022). Typically, channel widths are found to be about two to four times the width of associated splays. Using this information, a rough estimation of the Quarry Sandstone's parent river width, based on a 130-m-wide splay, would suggest a river width of ap- proximately 260 to 520 m. This range accounts for the variability in correlations observed across different flu- vial systems, including sediment supply, floodplain gra- dient, and river morphology. However, no suitable body of sandstone is present to the west or north of the Quar- ry Sandstone, making the crevasse splay or complex of multiple splays interpretation for the Quarry Sandstone questionable. During the formation of a crevasse or breach in the levee, spillage into the floodplain results in a divergence of currents from the crevasse, which is recorded in the preserved sediments even for lobate splays (Columbera and Mountney, 2021). This divergence is crucial for de- veloping wide and lobate splays (Figures 34B and 34C; Millard et al., 2017). However, no segment of the Quar- ry Sandstone preserves paleocurrents that can be back- traced to a crevasse splay. Furthermore, coarser sedi- ments in modern crevasse splays are deposited closer to the breakout point as the transport capacity of the unconfined flow rapidly decreases, while finer materi- als are carried farther away (Millard et al., 2017; Burns et al., 2019). The deceleration of crevasse water is even more rapid in standing water, such as swamps and lakes, which would restrict the dispersal of coarse grains and large bones to the most proximal part of the splay. The Quarry Sandstone shows no major reduction in the size or abundance of the coarse fraction at its western and eastern extremities when compared with the dinosaur quarry (Figure 35). The rapid drop in transport competence as the cre- vasse water spills onto the floodplain often causes the healing of the breach (Hajek and Wolinsky, 2012). This breach healing also occurs when log or debris jams develop at the mouth of the breach, acting as barriers that reduce water flow and sediment transport, thereby allowing sediment deposition to fill the crevasse. This phenomenon contributes to the difficulty of explaining how large bones could get into the distributary channel of a crevasse splay without the bone jams healing the crevasse. Our work updates the previous work of Peter- son (1980, 1984), who had identified paleo-anticlines based on localized thinning of the Salt Wash Member of the Morrison Formation in southern Utah. In dis- cussing the effects of these subsurface paleo-anticlines on syn-deposition, Peterson considered the paleo-an- ticlines as slight barriers to braided river flow, result- Figure 34. (A) Distribution channels (center below arrow) on the lower Mississippi River delta, serving as a model for the Quarry Sandstone as cited by Brezinski and Kollar (2018). The arrow indicates the direction of flow of the Mississippi River. (B and C) Crevasse splay development, Columbia River, British Columbia (50.9358°N., -116.4079°W.). (A) Early phase (Yan- dex Maps, undated). (B) 2004 (Google Earth). Note that most sediment is deposited proximally, with an increase in sediment divergence as the splay grows. 65 A River Runs Through It—The Quarry Sandstone and Adjacent Strata, Dinosaur National Monument, Utah Carpenter, K., and Taylor, L.H. Geology of the Intermountain West 2025 Volume 12 ing in coarser sediments being preferentially trapped in the paleo-synclines because the streams lacked the transport energy to move the sediments over the pa- leo-anticlines. Winnowed fine-grained sediments were deposited on and beyond the paleo-anticlines. How- ever, unresolved issues remain, including: (1) how did paleo-synclines downstream received coarse-grained sediments if they were trapped at the most upstream paleo-syncline-paleo-anticline pairs; (2) how did sed- imentation rates maintain a delicate balance to trap coarse grains in the paleo-synclines without forming lakes; and (3) why did the restricted flow over the an- ticlines not actually increase in transportation capacity due to increased velocity? Peterson (1980, 1984) pos- tulated that the paleo-anticlines were located near the position of modern anticlines and suggested that the modern anticlines were a Laramide reactivation of the paleo-anticlines. Our research on the Quarry Sandstone and accom- modation space associated with the proto-Split Moun- tain anticline suggests that the loss of accommodation space due to the paleo-anticlines can be shown by local- ized thinning of strata and the lateral aggregation and lateral interconnectedness of braided channel sandstone bodies. This interpretation suggests that switching the placement of the paleo-anticlines and paleo-synclines as determined by Peterson (1980, 1984) would resolve many of the problems with his model, and the matter becomes one of accommodation space, a concept that was not well-developed during Peterson’s time. CONCLUSION This comprehensive study of the Quarry Sandstone within the Morrison Formation provides critical insights into the depositional environment, sedimentological processes, and the geological influences that shaped this unique sedimentary deposit. By synthesizing new data and reassessing previous interpretations, this study re- inforces the view that the Quarry Sandstone represents braided river deposits, characterized by multithreaded channels and dynamic fluvial processes and the high width-to-thickness ratios of the sandstone bodies. Our research challenges the alternative interpreta- tion proposed by Brezinski and Kollar (2018), which suggested that the Quarry Sandstone formed as a cre- vasse splay complex. By critically evaluating the correla- tion between crevasse splay width and parent channel width, and by examining the distribution of coarse sedi- ments and paleocurrents, this study refutes the crevasse splay hypothesis, instead favoring a model of stacked braided river deposits influenced by tectonic activity. This study also highlights the role of tectonic fea- tures, particularly paleo-anticlines, in influencing sed- iment deposition within the Morrison Formation. The proposed proto-Split Mountain anticline likely played a significant role in shaping the Quarry Sandstone by re- ducing accommodation space, leading to the lateral ag- gregation of braided channel sandstone bodies and fre- quent avulsions. This tectonic influence aligns with the earlier work of Peterson (1980, 1984), who suggested that paleo-anticlines influenced local sediment transport. Figure 35. Comparison of the Quarry Sandstone at (A) the western end in Douglass Draw, (B) on the quarry face in the QEH, and (C) the eastern end near Swelter Shelter Draw, showing the absence of distal fining expected of a crevasse splay. Scales in cm. 66 A River Runs Through It—The Quarry Sandstone and Adjacent Strata, Dinosaur National Monument, Utah Carpenter, K., and Taylor, L.H. Geology of the Intermountain West 2025 Volume 12 Furthermore, this study provides a nuanced under- standing of the complex interactions between accom- modation space, sediment supply, and tectonic process- es, illustrating how these factors collectively influenced the depositional patterns within the Morrison Forma- tion. By revisiting and refining previous models, this re- search not only resolves longstanding questions about the formation of the Quarry Sandstone but also con- tributes to a broader understanding of fluvial dynamics in ancient, tectonically active regions. ACKNOWLEDGMENTS Our study builds upon the foundational work at Dinosaur National Monument (1990–1993) by Chris- tine Turner, U.S. Geological Survey, and the late Fred “Pete” Peterson (1933–2019), U.S. Geological Survey. We are grateful to Pete for his discussions on the Morri- son Formation and for sharing his stratigraphic sections from Dinosaur National Monument, which were used in Figures 5 and 6. We also thank Kevin Chamberlain, Department of Geology and Geophysics, University of Wyoming, for providing the calculated radiometric age. Thin sections were prepared by Wagner Petrographic, Lindon, Utah. We extend our thanks to Manja Hethke, Institute of Geological Sciences, Freie Universität Ber- lin, and Benjamin Sames, Department of Geodynamics and Sedimentology, University of Vienna, for providing information on the late Michael Schudack’s, Institut für Paläontologie, Freie Universität Berlin, ostracod and charophyte collection from Dinosaur National Mon- ument. Thanks to Diane Iverson, Sue Ann Bilbey, and Evan Hall (Uinta Paleontological Associates, Inc.) for sharing the Earl Douglass photographs. Fieldwork was conducted under National Park Service Scientific Re- search and Collecting Permits DINO-2019-SCI-0028, DINO-2020-SCI-0010, and DINO-2021-SCI-0008; we thank ReBecca Hunt-Foster of Dinosaur National Mon- ument for her assistance in expediting the permitting process. We thank Isaac Allred, Brigham Young Uni- versity-Idaho; Tom Chidsey, Utah Geological Survey; John Foster, Utah Field House of Natural History State Park Museum; ReBecca Hunt-Foster, Dinosaur Nation- al Monument; William Lund, Utah Geological Survey; Theresa Schwartz, U.S. Geological Survey; Douglas Sprinkel, Azteca Geosolutions; and Jianqiao Wang, Col- orado School of Mines, for their constructive reviews. This is the ninth installment in a series by the senior author on Dinosaur National Monument. REFERENCES Alexander, J., and Fielding, C.R., 2006, Coarse-grained floodplain deposits in the seasonal tropics—towards a better facies model: Journal of Sedimentary Research, v. 76, p. 539–556. Allen, P.A., 2017, Sediment routing systems—the fate of sed- iment from source to sink: New York, Cambridge Uni- versity Press, 407 p. 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Carpenter, K., and Taylor, L.H., 2025, A river runs through it—the Quarry Sandstone and adjacent strata, Dinosaur National Monument, Utah: Geology of the Intermountain West, v. 12, p. 25–74, https://doi.org/10.31711/giw.v12.pp25-74. 1 APPENDIX 1 Appendix 1 includes photographs and photomicrographs showing details of the various lithologies applicable to this study. Grain and fossil content are included. Details included in the Appendix 1 figure captions are presented in chart form in Appendix 2. Figure A1. Sandy mudstone (DINO 45151). Poorly sorted, silty, sandy mudstone containing some grains from an igneous source. Grains include quartz, chert, microcline feldspar, and rock fragments. Coarse fraction ranges from medium to very coarse, angular to subrounded grains (0.4 to 1.6 mm). Silt component 16 µm to 300 µm, with angular to subangular grains predominately of quartz and minor amounts of chert, chalcedony, microcline feldspar, glaucony, rock fragments, hornblende(?), pyrite, and biotite. Calcite crystals about 6 µm. Quartz overgrowths, calcite replacement, and evidence of dissolution are present. Some quartz grains exhibit undulose extinction, a sign of stress. This suggests probable igneous source, as other signs of stress are absent. (A) Oriented hand sample of distal crevasse splay sandy mudstone, with matrix supported, unsorted angular chert and quartz grains. Purple pedogenic mottling. One unit on the scale is 1.0 mm. (B) Partial thin section showing unsorted angular to subrounded siliciclastic grains. One unit on the scale is 1.0 mm. (C) Plane-polarized light of silt- and sand-bearing, calcareous mudstone. One unit on the scale is 30.0 µm. (D) Crossed nicols of a rock fragment containing silt grains (white). The rock fragment has a partial rim of organic material (arrows). One unit on the scale is 0.1 mm. (E) Quartz grain showing dissolution (arrow). One unit on the scale is 0.3 µm. https://doi.org/10.31711/giw.v12.pp25-73 Carpenter, K., and Taylor, L.H., 2025, A river runs through it—the Quarry Sandstone and adjacent strata, Dinosaur National Monument, Utah: Geology of the Intermountain West, v. 12, p. 25–74, https://doi.org/10.31711/giw.v12.pp25-74. 2 Figure A2. Mudstone (DINO 45150). Slightly silty and sandy calcareous mudstone (calcite crystals 2 to 5µm) with 2% to 3% grain content. Most grains are quartz, with chert (much less than 1%) and mica (much less than 1%) less common. Stressed quartz grains, probably from a volcanic source, are relatively common. Some quartz grains are fractured. One compacted fine sand grain (0.4 x 0.25 mm) consists of both chalcedony and chert. Rare large grains of angular chert up to 0.4 x 0.3 mm are present. A few grains consist of glaucony. One large (1.86 x 1.41 mm) angular fragment consisting of peloids, a portion of which are glaucony. Pyrite is present but rare. There is a small amount of organic matter present. Dark organic pellets are common. Grains exhibit calcite or organic material coating. Minor dissolution of quartz and calcite replacement are present. There is also evidence of possible pre- and post-depositional fracturing and later silica cementation and calcite cementation, and possible recrystallization. The post-depositional diagenesis may be related to tectonism. Fossils present include burrows and rhizoliths. (A) Hand sample polished parallel to bedding. One unit on the scale is 1.0 mm. (B) Partial thin section, contrast enhanced to reveal details. Abbreviations: b – burrow; r – rhizoliths. Upper right white streak is a crack made during polishing. One unit on the scale is 1.0 mm. (C) Plane-polarized light view of calcareous mudstone with minor quartz grains (white). One unit on the scale is 30 µm. (D) Crossed nicols view of grains in calcareous mudstone matrix. Quartz grain with calcite cement rim (left) and stressed quartz with filled fracture (arrow). One unit on the scale is 8.0 µm. (E) Plane-polarized light view of a subrounded quartz grain with fracture (white arrow). Portion of the grain appears to be partially dissolved and replaced by microcrystalline calcite (red https://doi.org/10.31711/giw.v12.pp25-73 Carpenter, K., and Taylor, L.H., 2025, A river runs through it—the Quarry Sandstone and adjacent strata, Dinosaur National Monument, Utah: Geology of the Intermountain West, v. 12, p. 25–74, https://doi.org/10.31711/giw.v12.pp25-74. 3 arrow). Also, a rim of organic material (yellow arrow). One unit on the scale is 0.3 µm. (F) Grain (0.4 x 0.25 mm) consisting of compressed calcedony and chert (arrow) in plane polarized light (left) and crossed nicols (right) views. (G) Plane-polarized light view showing green glaucony grains (arrows). One unit on the scale is 8.0 µm. Figure A3. Laminated, silt-rich, sand-bearing, calcite-cemented mudstone with mud clasts (DINO 45153). Contains dark, organic-rich component and a lighter component, both with about 50% silt grains (8 to 25 µm) and far fewer (3% to 10%) sand grains (90 to 160 µm). The angular to subangular grains are predominantly quartz, with minor amounts of chert, biotite, and hornblende. Rare quartz grains exhibit undulose extinction, a sign of stress. This suggests probable igneous source, as other signs of stress are absent. Some darker clay clasts are present and contain silt-filled fractures, suggesting fracturing during deposition. (A) Polished hand sample in cross section. One unit on the scale is 1.0 mm. (B) Thin section oriented perpendicular to bedding, as deposited with up at the top, showing poorly laminated structure and scattered light and dark mud clasts. Contrast enhanced. Irregular fractures are also present in original hand sample. One unit on the scale is 1.0 mm. (C) Plane-polarized light view showing the light component of thin section. The arrow points to organic material. One unit on the scale is 30 µm. (D) Plane-polarized light view showing the darker, organic-rich components of thin section. Note the horizontal arrangement of grains in both. One unit on the scale is 30 µm. https://doi.org/10.31711/giw.v12.pp25-73 Carpenter, K., and Taylor, L.H., 2025, A river runs through it—the Quarry Sandstone and adjacent strata, Dinosaur National Monument, Utah: Geology of the Intermountain West, v. 12, p. 25–74, https://doi.org/10.31711/giw.v12.pp25-74. 4 Figure A4. Fossil-bearing calcareous mudstone concretion (DINO 45145). Carbonate grains range from 1 to 12 µm. Quartz grains range from 25 µm (medium silt) to 128 µm (fine sand). Calcite-filled septarian cracks are present. Fossils that compose 5% to 10% of the mudstone are ostracod and diplostracan carapaces. Geopetal structures exhibited by some ostracod carapaces indicate their orientation prior to deposition as individual grains. Single carapaces and fragmentary carapaces indicate turbulent transportation. (A) Oriented with up at the top, a nodule thin section showing septarian cracks filled with calcite, and a zone of ostracod and diplostracan carapaces above dark, organic-rich zone. Contrast enhanced to show detail. One unit on the scale is 1.0 mm. (B) Plane-polarized light view showing abundant, randomly oriented ostracod carapace fragments and single carapaces in silty mudstone matrix. Small white grains are quartz. One unit on the scale is 30 µm. (C) Plane-polarized light view showing closed ostracod carapaces exhibiting geopetal structures. Note scattered small dark organic pellets in the matrix. One unit on the scale is 12.5 µm. (D) Calcite-filled fracture under plane-polarized light. One unit on the scale is 30 µm. (E) Same calcite-filled fracture under crossed nicols. One unit on the scale is 30 µm. https://doi.org/10.31711/giw.v12.pp25-73 Carpenter, K., and Taylor, L.H., 2025, A river runs through it—the Quarry Sandstone and adjacent strata, Dinosaur National Monument, Utah: Geology of the Intermountain West, v. 12, p. 25–74, https://doi.org/10.31711/giw.v12.pp25-74. 5 Figure A5. Fine-grained, fossil-rich, calcite- and clay-cemented nodule (DINO 45154). Mottled nodule contains two components. The darker, organic-rich component includes clasts up to 1.75 mm in greatest dimension. The clasts contain spherical peloids about 8 to 10 µm in diameter. Medium to coarse silt grains (25 to 40 µm) are present in both components, but represent less than 1% of the lithology. Most silt grains are quartz, with rare chert, glaucony, olivine, and chalcedony present. The light component contains about 3% to 5% ostracod and diplostracan carapaces and some paired ostracod carapaces that reach 0.35 mm in length. Some closed ostracod carapaces have geopetal filling indicating their original orientation. Single and fragmentary carapaces indicate turbulent transportation. Calcite crystals (2 to 6 µm) fills voids created by dissolution of fossils. Fractures within both components are also filled with calcite cement. The calcite crystals in the fractures reach 0.74 mm in greatest dimension. Nodule is interpreted as pedogenetic modification of a distal splay pond deposit. (A) Cut surface of nodule showing internal pedogenetic fracturing, incorporated clasts during nodule growth, and rhizoliths. Slight contrast enhancement. One unit on the scale is 1.0 mm. (B) Reversely oriented relative to Figure A5A, this is a view of an unstained partial thin section with a pedogenetically fractured dark clast with calcite infilling (right) and calcite-filled rhizoliths (left). Contrast enhanced. One unit on the scale is 1.0 mm. (C) Crossed nicols view showing an olivine crystal (blue and red) surrounded by calcite. One unit on the scale is 0.3 µm. (D) Plane-polarized light view of the dark component showing clasts that contain quartz silt grains. The interclastic area is filled with calcite cement. One unit on the scale is 30 µm. (E) Oriented plane-polarized light view showing the contact between the light and dark components. Note contrast in grain sizes, and probable fungal mycelium https://doi.org/10.31711/giw.v12.pp25-73 Carpenter, K., and Taylor, L.H., 2025, A river runs through it—the Quarry Sandstone and adjacent strata, Dinosaur National Monument, Utah: Geology of the Intermountain West, v. 12, p. 25–74, https://doi.org/10.31711/giw.v12.pp25-74. 6 trace in center of image. One unit on the scale is 30 µm. (F) Plane-polarized light view of the light component showing calcite-filled ostracod and diplostracan carapaces. One unit on the scale is 30 µm. Figure A6. Fossil-bearing, silt-rich, pellet-rich, calcareous mudstone nodule (DINO 45146). This mottled calcareous nodule consists of small- and larger-grained matrices. The finer matrix material consists of 1 to 2 µm grains or crystals, and the coarser matrix consists of about 8 µm grains or crystals. Quartz grains dominate and range from 40 µm (coarse silt) to 112 µm (very fine sand), often with a calcite cement coating. Less abundant grains include much less than 1% chert, glaucony, microcline feldspar, and possible hornblende. Stressed quartz from a high temperature, probably volcanic, origin, and compacted grains are also present. One coarse sand-sized chert grain (0.1 mm) is present. Fossils and ichnofossils include numerous burrows, ostracod carapaces, much less than 1% of possible charophyte fragments, ostracod calcite steinkerns[?], disarticulated carapaces, and organic pellets about 15 µm in size. (A) Entire thin section with numerous burrows (some indicated by arrows). Contrast increased to bring out burrows. One unit is 1.0 mm. (B) Plane-polarized light view of silt-rich calcareous mudstone. Silt and sand grains are white. The curved white feature is an ostracod carapace. One unit is 30 µm. (C) Crossed nicols view of a quartz grain with a calcite cement rim. One unit on the scale is 8.0 µm. (D) Crossed nicols view of a rock fragment with a calcite cement rim. One unit on the scale is 8.0 µm. (E) Crossed nicols view of a compacted grain composed of quartz (gray) grain on the right and chert (black) on the left. One unit on the scale is 0.3 µm. (F) Plane-polarized light view of a curved calcite-filled charophyte fragment. Note the presence of silt grains (white) to the left the charophyte. One unit on the scale is 8.0 µm. https://doi.org/10.31711/giw.v12.pp25-73 Carpenter, K., and Taylor, L.H., 2025, A river runs through it—the Quarry Sandstone and adjacent strata, Dinosaur National Monument, Utah: Geology of the Intermountain West, v. 12, p. 25–74, https://doi.org/10.31711/giw.v12.pp25-74. 7 Figure A7. Silt- and sand-bearing, calcareous mudstone nodule (DINO 45149). The nodule is mottled. The dark component is fine calcareous mudstone (calcite crystals 2 to 4 µm) encasing dark peloids containing fine to fine silt (5 to 30 µm) grains. The mostly angular grains are predominantly quartz, with minor (much less than 1%) chert and biotite grains and glaucony present. The light component is coarse calcareous mudstone (80 µm calcite crystals) containing angular to subrounded, medium silt to fine sand quartz and less common chert grains (27 to 170 µm). This component contains much less than 1% biotite and glaucony grains. Rare pyrite grains are present. Some stressed quartz grains are present, indicating a high temperature source, probably volcanic. The edges of some quartz grains are partially dissolved and contain calcite on the edges, perhaps the result of partial replacement. Some quartz grains are compacted due to pressure on the original source of the quartz. There are rare voids filled with calcite cement. Rounded organic fragments reach 45 µm in greatest dimension. Fossils include rare ostracod carapaces that were dissolved and the voids filled with sparry calcite cement. (A) Oriented entire thin section showing micro-rhizolith (arrow) and load cast (center). Contrast enhanced. One unit on scale is 1.0 mm. (B) Detail of micro-rhizolith, entire scale is 5.0 mm. (C) Plane-polarized light view of silt-and sand-bearing calcareous mudstone. One unit on the scale is 80 µm. (D) Plane-polarized light view of a curved ostracod fragment in a calcareous mudstone matrix containing angular quartz (white) and non-quartz grains (dark). One unit on the sale is 30 µm. (E) Crossed nicols view showing two larger grains. Right grain (black and gray) is a compacted quartz grain. Left grain is quartz partially replaced by calcite. The dark brown areas are organic pelletal material. The lighter areas are calcareous mudstone. One unit on the scale is 8.0 µm. https://doi.org/10.31711/giw.v12.pp25-73 Carpenter, K., and Taylor, L.H., 2025, A river runs through it—the Quarry Sandstone and adjacent strata, Dinosaur National Monument, Utah: Geology of the Intermountain West, v. 12, p. 25–74, https://doi.org/10.31711/giw.v12.pp25-74. 8 Figure A8. Silt- and sand-bearing, calcareous mudstone nodule (DINO 45152). Calcareous, mottled mudstone (calcite crystals 2 to 6 µm) with 10% to 15% grains floating in the matrix. The angular to subrounded medium to coarse silt (26 to 52 µm) and fine to coarse sand grains (169 to 580 µm) are predominantly quartz, with minor amounts of chert, chalcedony, microcline feldspar, and biotite. Some quartz is stressed, suggesting a high temperature source, probably volcanic. Calcite cement to 65 µm thick is visible on the edges of the grains. (A) Polished hand sample oriented perpendicular to bedding, showing matrix-supported grains and mud clasts (arrow). One unit on the scale is 1.0 mm. (B) Unstained, oriented thin section with up at the top showing matrix supported unsorted, angular to subrounded siliciclastic grains and dark organic-enriched matrix. Contrast enhanced. One unit on the scale is 1.0 mm. (C) Plane-polarized light view of stained silt-bearing calcareous mudstone. One unit on the scale is 30 µm. Letters refer to images (D) and (E). (D) Crossed nicols view of a stressed quartz grain with a calcite cement coating. One unit on the scale is 8.0 µm. (E) Crossed nicols view of a chert grain with a calcite cement coating. One unit on the scale is 8.0 µm. Figure A9. Silt-bearing calcareous nodule (DINO 45158). Nodule containing about 10% fine silt to very fine sand grains (14 to 80 µm). Organic clasts are present, represented by areas about 180 µm in greatest dimension. Sparry calcite coats many of the grains and organic clasts. (A) Whole thin section of nodule. Note color zonation. Contrast enhanced. One unit on the scale is 1 mm. (B) Plane-polarized light view of light-colored part of the nodule. One unit on the scale is 30 µm. (C) Plane-polarized light view of the dark part of the nodule. One unit on the scale is 30 µm. https://doi.org/10.31711/giw.v12.pp25-73 Carpenter, K., and Taylor, L.H., 2025, A river runs through it—the Quarry Sandstone and adjacent strata, Dinosaur National Monument, Utah: Geology of the Intermountain West, v. 12, p. 25–74, https://doi.org/10.31711/giw.v12.pp25-74. 9 Figure A10. Silt-bearing calcareous mudstone nodule (DINO 45159). This calcareous mudstone nodule (calcite crystals 3 to 4 µm) contains about 3% grains. The angular and subrounded grains are predominantly quartz and chert. They have a bimodal distribution of coarse silt to very fine grained sand (40 to 120 µm) and fine-grained sand (170 to 220 µm). Medium sand is present, but very rare. One round grain is 450 µm in diameter. Many of the grains are coated with microcrystalline calcite. (A) Partial thin section showing clay matrix-supported silt grains. Contrast enhanced. One unit on the scale is 1.0 mm. (B) Crossed nicols view showing quartz grains with calcite cement coatings. One unit on the scale is 0.3 µm. (C) Crossed nicols view showing silt grains (white) and larger quartz sand grains (dark) with calcite cement coating. One unit on the scale is 30 µm. https://doi.org/10.31711/giw.v12.pp25-73 Carpenter, K., and Taylor, L.H., 2025, A river runs through it—the Quarry Sandstone and adjacent strata, Dinosaur National Monument, Utah: Geology of the Intermountain West, v. 12, p. 25–74, https://doi.org/10.31711/giw.v12.pp25-74. 10 Figure A11. Silt-rich, calcareous-cemented, calcareous mudstone nodule (DINO 45161). This mottled silt- rich mudstone nodule consists of about 40% grains. The coarse silt grains (about 40 µm) and rare medium sand (to 275 µm) are predominantly quartz. Additional grains (greater than 1%) consist of chert, stressed quartz, biotite, olivine, and hornblende. The stressed grains suggest a high temperature source, probably volcanic. Mudstone clasts reach 360 µm in greatest dimension. Fossils are rare, often visible as recrystallized calcite shadows. Intergranular and coating calcite cements are sparry and microcrystalline calcite. Silica cement fills fractures, but is less common than calcite cement. (A) Polished hand sample oriented perpendicular to bedding, showing pedogenic fracturing and brecciation. Dark lenticular object is a mudstone clast. One unit on the scale is 1.0 mm. (B) Oriented with up at the top, thin section view showing light silty zone bracketed by darker, organic-rich silty zones. Pedogenic brecciation in upper zone. Few scattered burrows. Contrast enhanced. One unit on the scale is 1 mm. (C) Plane-polarized light view of silt- rich calcareous mudstone with round clay clasts (dark) and angular to rounded silt grains. Many of the grains and casts exhibit calcite cement coatings. One unit on the scale is 30 µm. (D) Plane-polarized light view of silty, sandy calcareous mudstone. One unit on the scale is 30 µm. (E) Crossed nicols view of a quartz grain which exhibits a microcrystalline calcite cement rim (arrow). Microcrystalline calcite also fills the void above the quartz grain. One unit on the scale is 8.0 µm. (F) Crossed nicols view of brecciation zone, with angular mudstone clasts cemented by intergranular sparry calcite cement (arrow). Quartz grains (white and gray) can be seen within the clasts and surrounded by the calcite cement. One unit on the scale is 12.5 µm. https://doi.org/10.31711/giw.v12.pp25-73 Carpenter, K., and Taylor, L.H., 2025, A river runs through it—the Quarry Sandstone and adjacent strata, Dinosaur National Monument, Utah: Geology of the Intermountain West, v. 12, p. 25–74, https://doi.org/10.31711/giw.v12.pp25-74. 11 Figure A12. Fossil-rich, calcite- and clay-cemented nodule (DINO 45162). Silty and clay-rich calcareous mudstone with 10% to 15% whole and fragmentary ostracod valves. Whole ostracods filled with sparry calcite. (A) Entire thin section showing concretionary banding. One unit on the scale is 1 mm. (B) Plane- polarized light view showing ostracod debris in calcareous mudstone. One unit on the scale is 30 µm. (C) Calcite-filled ostracod within calcareous mudstone. Left view under plane-polarized light, right view under crossed nicols. One unit on the scale is 0.3 µm. (D) Crossed nicols view showing two quartz grains coated with calcite in a calcareous mudstone matrix. On unit on the scale is 0.3 µm. (E) Crossed nicols view of quartz grain coated with silica and a secondary coating of calcite (arrow). Multicolored grain to the right is calcite. One unit on the scale is 0.3 µm. https://doi.org/10.31711/giw.v12.pp25-73 Carpenter, K., and Taylor, L.H., 2025, A river runs through it—the Quarry Sandstone and adjacent strata, Dinosaur National Monument, Utah: Geology of the Intermountain West, v. 12, p. 25–74, https://doi.org/10.31711/giw.v12.pp25-74. 12 Figure A13. Silty limestone (DINO 45156). Silty, clay-rich (about 2 µm crystals) calcareous mudstone with minor (about 1%) ostracod valve fragments. Organic peloids (about 15 µm) and clasts (about 0.5 mm) present. Rare (less than 1%) grains (13 µm to 117 µm) are quartz with fewer chert, chalcedony, biotite, and glauconite grains. Grains coated with calcite cement; some quartz grains partially replaced by microcrystalline calcite. Calcite-filled porosity abundant (0.45 to 1.2 mm). Few ostracod valve fragments. (A) Thin section showing scattered organic-rich areas (e.g., arrow). One unit on the scale is 1 mm. (B) Plane-polarized light view of ostracod valve porosity and other voids filled with calcite. Dark material is organic matter (arrow). Note the presence of clear white grains. One unit on the scale is 30 µm. (C) Crossed nicols view of a quartz grain with sparry calcite rim (arrow) and small replacement calcite crystals within the grain. One unit on the scale is 0.3 µm. (D) Plane-polarized light view of interclastic porosity filled with calcite cement. One unit on the scale is 30 µm. (E) Plane-polarized light view showing chert grains (dark) with sparry calcite with calcite rim and fossil porosity filled with sparry calcite (white). Note the dark claystone matrix, other grains, and calcite-filled porosity. One unit on the scale is 12.5 µm. https://doi.org/10.31711/giw.v12.pp25-73 Carpenter, K., and Taylor, L.H., 2025, A river runs through it—the Quarry Sandstone and adjacent strata, Dinosaur National Monument, Utah: Geology of the Intermountain West, v. 12, p. 25–74, https://doi.org/10.31711/giw.v12.pp25-74. 13 Figure A14. Silica and clay clasts with in situ brecciation suspended in calcareous mudstone (DINO 45163). Mottled calcareous mudstone and organic-rich silica and clay clasts surrounded by sparry calcite (crystals to 60 µm), and with calcite coating. Clasts 0.25 to 0.1 mm, angular to subrounded, some with internal fractures and organic pellets within them. Some clasts may be from rock fragments. Shadows of very fine grained calcareous mudstone (crystals to 20 µm) present. A single mollusk shell fragment is present; rare ostracod valves are present in the matrix and within some clasts. (A) Entire thin section slide showing upward coarsening of clasts and in situ brecciation within a matrix of calcareous mudstone (see also Figure A15D another example). F refers to large clast shown in image F. One unit on the scale is 1 mm. (B) Plane- polarized light view of dark organic pellets within a micritic clast. One unit on the scale is 0.3 µm. (C) Plane-polarized light view of clasts within sparry calcite matrix. One unit on the scale is 30 µm. (D) Plane- polarized light view of in situ brecciation of clasts. Arrow shows incipient fracture. Each mark on the scale is 30 µm. (E) Plane-polarized light view of organic clast with sparry calcite coating (arrow). Other smaller clasts within the calcareous mudstone matrix. One unit on the scale is 12.5 µm. (F) Plane-polarized light view of a large clast with a seam of sparry calcite cement (arrow). Clast is identified as F in image A. One unit on the scale is 30 µm. (G) Plane-polarized light view showing curved mollusk shell fragment (arrow) within calcareous mudstone matrix. Organic clasts are brown and dark brown. One unit on the scale is 12.5 µm. https://doi.org/10.31711/giw.v12.pp25-73 Carpenter, K., and Taylor, L.H., 2025, A river runs through it—the Quarry Sandstone and adjacent strata, Dinosaur National Monument, Utah: Geology of the Intermountain West, v. 12, p. 25–74, https://doi.org/10.31711/giw.v12.pp25-74. 14 Figure A15. Organic-rich limestone (DINO 45164). Tan organic-rich, with about 3% to 5% grain component. Grains size bimodal size: about 10 µm (fine silt) most common and fewer (about 115 µm) very fine sand grains. Grains predominantly quartz with rare (less than 1%) chert, glauconite, and stressed quartz indicating a volcanic source. Some grains compressed, the result of high pressure. (A) Partial thin section slide showing rhizoliths with iron halos in cross-section (arrows). One unit on the scale is 1.0 µm. (B) Plane-polarized light view of brown calcareous mudstone with silt and sand grains (white). One unit on the scale is 30 µm. (C) Plane-polarized light view of a polycrystalline quartz grain. Each unit on the scale is 0.3 µm. (D) Cross nicols view of quartz grain in image C. One unit on the scale is 0.3 µm. (E). Rhizoliths with halos under plane-polarized light (left) and cross nicols (right) views. One unit on the scale is 30 µm. https://doi.org/10.31711/giw.v12.pp25-73 Carpenter, K., and Taylor, L.H., 2025, A river runs through it—the Quarry Sandstone and adjacent strata, Dinosaur National Monument, Utah: Geology of the Intermountain West, v. 12, p. 25–74, https://doi.org/10.31711/giw.v12.pp25-74. 15 Figure A16. Fine- to medium-crystalline, clay-rich limestone (DINO 45144). The fine to medium-grained calcite matrix (crystals 0.1 to 12 µm) contains a very rare coarse silt component with grains reaching about 48 µm. Pyrite is present, but rare. Clay clasts from 0.24 to 0.46 mm are present. Some clasts are broken with calcite cement visible between separated fragments. Organic pellets are present. Fossils present include ostracods and diplostracan branchiopods. Many were dissolved, resulting in calcite-filled voids. (A) Thin section oriented as deposited. Contrast enhanced to bring out subtle details. Area outlined in white is enlarged in Figure A16C. One unit on scale is 1.0 mm. (B) Plane-polarized light view of calcite-cemented fine mudstone with calcite-filled voids, many of which were formed by ostracod shells dissolution. Image slightly enhanced to better show ostracod carapace fragments. One unit on the scale is 30 µm. (C) Enlargement from image A showing part of a fossil soil fungal mycelium, a mass of hyphae that absorbs nutrients. Color contrast enhanced. One unit on scale is 100 µm. (D) Crossed nicols view showing in situ pedogenetically fractured clay clasts. Note how the fragments fit together and are cemented by calcite. See also Figure A13. One unit on the scale is 12.5 µm. (E) Crossed nicols view of calcite filled ostracod. One unit on the scale is 12.5 µm. https://doi.org/10.31711/giw.v12.pp25-73 Carpenter, K., and Taylor, L.H., 2025, A river runs through it—the Quarry Sandstone and adjacent strata, Dinosaur National Monument, Utah: Geology of the Intermountain West, v. 12, p. 25–74, https://doi.org/10.31711/giw.v12.pp25-74. 16 Figure A17. Finely crystalline, organic-rich muddy limestone (DINO 45155). One of the few, purple-tinted limestones, this finely crystalline (calcite crystals about 6 µm), mottled muddy limestone is organic rich, and contains about 3% grains. Thin laminations or lenses of organic-rich clay are present. Very fine to medium silt grains (5 to 25 µm) consist of quartz with rare chert and biotite grains present. One organic- rich clast (about 0.5 mm) is partially coated with a about 30-µm-thick quartz cement. Quartz-filled fractures are up to about 30 µm wide. Organic material and quartz cement fill rare pores that reach 1.2 mm in size. (A) View of a polished hand sample showing weak laminations and mottling. One unit on the scale is 1.0 mm. (B) Thin section oriented perpendicular to bedding, with up at the top, showing two cycles of fining upwards silt. Slightly burrowed. Contrast is enhanced. One unit on the scale is 1.0 mm. (C) Plane-polarized light view showing the contact between lamina across the middle of the thin section. One unit on the scale is 30 µm. (D) Crossed nicols view of a silica-filled fracture. One unit on the scale is 0.3 µm. (E) Crossed nicols showing an organic-rich clast exhibiting a partial quartz cement coating. Black organic material can be seen on the right side of the grain (arrow). One unit on the scale is 0.3 µm. https://doi.org/10.31711/giw.v12.pp25-73 Carpenter, K., and Taylor, L.H., 2025, A river runs through it—the Quarry Sandstone and adjacent strata, Dinosaur National Monument, Utah: Geology of the Intermountain West, v. 12, p. 25–74, https://doi.org/10.31711/giw.v12.pp25-74. 17 Figure A18. Slightly silty and sandy limestone (DINO 45157). Calcareous mudstone with very minor (less than 1%) silt and sand component. Matrix with grains or crystals about 6 µm. Quartz grains predominant, with minor biotite, glauconite, and possible olivine grains present. Grain size about 30 µm (medium silt) with rare grains to 90 µm (very fine grained sand). Secondary calcite coating on grains and organic clasts. Organic clasts to 0.5 mm, with silt grains incorporated. (A) Polished hand sample with manganese dendrites along edges. One unit on scale is 1.0 mm. (B) Thin section, oriented perpendicular to bedding and with up at the top, showing burrows (arrows). One unit on the scale is 1 mm. (C) Plane-polarized light view of calcareous mudstone with silt and sand grains (white) and dark organic clast with a calcite rim. One unit on the scale is 30 µm. (D) Crossed nicols view of organic clasts (Botryoccus?) with a calcite rim. One unit on the scale is 0.3 µm. https://doi.org/10.31711/giw.v12.pp25-73 Carpenter, K., and Taylor, L.H., 2025, A river runs through it—the Quarry Sandstone and adjacent strata, Dinosaur National Monument, Utah: Geology of the Intermountain West, v. 12, p. 25–74, https://doi.org/10.31711/giw.v12.pp25-74. 18 Figure A19. Bioturbated, clay-rich, silt- and sand-bearing limestone (DINO 45160). This mottled, clay-rich, silt- and sand-bearing calcareous mudstone consists of dark and light components. The dark component consists of fine to medium-grained silt (4 to 10 µm) and with rare coarse silt (to 60 µm) grains. The light component consists of clay (1.5 to 2 µm) containing very rare fine silt grains. Quartz is the dominant grain mineral, with fewer grains of biotite, glaucony, and hornblende. The dark coarse component includes clasts of the finer light component, most likely the result of bioturbation. Fossils are rare, consisting of calcite- filled dissolved ostracod and/or diplostracan carapaces. (A) Hand sample oriented perpendicular to bedding showing pedogenic mottling, extensive burrowing, and a few thin rhizoliths. One unit on the scale is 1.0 mm. (B) Thin section, oriented perpendicular to bedding and with up at the top, showing mottling, burrows, and dark, organic-rich, clay-supported silt grains. One unit on the scale is 1.0 mm. (C) Plane-polarized light view of calcareous mudstone with silt and sand grains (white). One unit on the scale is 30 µm. (D) Plane- polarized light view showing a contact between the relatively grain-free light clay area and darker area of clay-supported silt grains. Note burrow at far left. One unit on the scale is 30 µm. https://doi.org/10.31711/giw.v12.pp25-73 Carpenter, K., and Taylor, L.H., 2025, A river runs through it—the Quarry Sandstone and adjacent strata, Dinosaur National Monument, Utah: Geology of the Intermountain West, v. 12, p. 25–74, https://doi.org/10.31711/giw.v12.pp25-74. 19 Figure A20. Fossiliferous, clay-rich limestone (DINO 45710). Mottled in part, with abundant clays. Ostracods, charophyte, and conchostracan fossils represent about 10% to 15% of sample. Most are fragments. The dark features of the mottled texture are clay clasts or the result of bioturbation. The dark features are about 3 mm in greatest dimension. Angular to subrounded silt grains (5 to 45 µm) represent less than 1% of the sample. Most are quartz, some of which is stressed quartz, indicating a volcanic source. Microcline feldspar and glauconite are present, but extremely rare. Some quartz grains are partially dissolved, with finely crystalline calcite around and within them, perhaps the result of partial replacement. Other quartz grains are coated with clays or, less commonly, calcite. Rare angular fragments (to 385 µm in longest dimension) consisting of calcite and quartz appear to represent material from an external origin. They contain fossil fragments and appear to represent partial silicification of calcite crystals. The presence of erosional fragments supports a depositional environment of origin. Original pores are uncommon, and appear to have resulted from fossil dissolution. They are lined with fine-grained calcite crystals (about 40 µm) and filled with larger calcite crystals (about 210 µm), representing two separate calcite cementation events. A single calcite-filled fracture (35 µm wide; 0.3 mm long) is present. (A) Thin section showing calcite-filled voids. One unit on the scale is 1.0 mm. (B) Plain-light view showing abundant clay (white) https://doi.org/10.31711/giw.v12.pp25-73 Carpenter, K., and Taylor, L.H., 2025, A river runs through it—the Quarry Sandstone and adjacent strata, Dinosaur National Monument, Utah: Geology of the Intermountain West, v. 12, p. 25–74, https://doi.org/10.31711/giw.v12.pp25-74. 20 and calcite (red). Calcite is stained with Alizarin Red-S. Entire scale is 0.5 mm. (C) Plane-polarized light view of compressed quartz (gray) and chert (black and gray) grains surrounded by calcareous mudstone matrix. One unit on the scale is 0.3 µm. (D) Plane-polarized light view showing abundant fossil fragments and a calcite-filled diplostracan at the top (arrow). One unit on the scale is 30 µm. (E) Plane polarized light view of probable clast of eroded fossiliferous, siliceous limestone. One unit on the scale is 8.0 µm. (F) Plane-polarized light view showing clay clast consisting of brown and gray components and containing a single quartz grain (arrow). One unit on the scale is 0.3 µm. (G) Crossed nicols view showing quartz grain with clay coating. One unit on the scale is 0.3 µm. (H) Plane-polarized light view of calcite-filled charophytes in cross section. One unit on the scale is 30 µm. (I) Plane-polarized light view of amorphous organic material. One unit on the scale is 30 µm. (J). Plane-polarized light view of a calcite-filled former void. Two stages of calcite precipitation are visible: microcrystalline calcite lining the pore is followed by larger sparry calcite crystals filling the remaining void space. One unit on the scale is 0.3 µm. Figure A21. Clay-rich limestone (DINO 45711). Mottled with abundant clays. Ostracods and charophyte (green algae) specimens are present but rare. The dark portions of the mottled texture are calcareous clay clasts. They contain fewer grains (less than 1%) than the lighter portion of the specimen. Angular to subrounded silt and very fine sand grains represent 7% to 10% of the sample. Most grains are quartz, some of which is stressed quartz, indicating either a high-temperature source or metamorphic alteration. Biotite mica is present, but extremely rare. Edges of some quartz grains are partially dissolved and with finely crystalline calcite around and within them, perhaps the result of partial replacement. Other quartz grains are coated with clays or, less commonly, calcite. Original pores, uncommon, and most likely resulting from https://doi.org/10.31711/giw.v12.pp25-73 Carpenter, K., and Taylor, L.H., 2025, A river runs through it—the Quarry Sandstone and adjacent strata, Dinosaur National Monument, Utah: Geology of the Intermountain West, v. 12, p. 25–74, https://doi.org/10.31711/giw.v12.pp25-74. 21 fossil dissolution, are lined with fine-grained calcite crystals (about 40 µm) and filled with larger calcite crystals (about 210 µm), representing two separate calcite cementation events. Some original pores contain large crystals of both calcite and quartz. (A) Thin section showing faint mottling. One unit in the scale is 1.0 mm. (B) Plain-polarized light view showing abundance of clay (light tan). Darker areas are calcite. Entire scale is 1.0 mm. (C) Plane-polarized light view showing mottled texture with dark clasts containing fewer silt grains than the lighter areas. Note the presence of an ostracod valve in the lower center. One unit on the scale is 30 µm. (D) Plane-polarized light view of a once open void, most likely resulting from dissolution of a fossil, filled with calcite (pink) and quartz (white and gray). Calcite is stained with Alizarin Red-S. One unit on the scale is 0.3 µm. (E) Plane-polarized light view of an angular quartz grain partially replaced with microcrystalline calcite (pink). Calcite is stained with Alizarin Red-S. One unit on the scale is 8.0 µm. (F) Same grain as shown in Figure A21E, under crossed nicols. One unit on the scale is 8.0 µm. (G) Plane-polarized light view of an ostracod valve fragment within a calcite filled ostracod. One unit on the scale is 12.5 µm. (H) Plane-polarized light view of a calcite-filled charophyte. One unit on the scale is 30 µm. https://doi.org/10.31711/giw.v12.pp25-73 Sheet1 Appendix Figure Catalog number Location Lithology Occurence Mottled Lamination Silt Sand Ostracod Diplostracan Charophyte Peloids Dissolution Recrystalline Replaced Spar Microcrystalline cement Quartz cement Clay cement Clay coat Compact % Grains Grain Size (Mm, except as labeled) Grain Shape fractures Organics Clay Quartz Stressed Quartz Fractured quartz Polycrystalline quartz Feldspar Chert Chalcedony Glauconite Biotite Pyroxene Hornblende Olivine Rock fragment Calcite Silt Sandstone subangular - subround Calcite fill Quartz fill A1 DINO 45151 west side QEH muddy sandstone bed x x ~40 ~6 0.4 - 0.5 mm angular- round x x x x x x x x ? x A2 DINO 45150 west side QEH mudstone bed x x in clast x x x x x 2-3 0.4-1.6 mm angular - subround x x x x x x x x A3 DINO 45153 West side QEH mudstone bed x 50 8 - 12 to 90 - 160 silt fill x clasts x x x x x A4 DINO 45145 East side QEH mudstone concretion x x x x ~2 1 - 12 25 - 128 x x x A5 DINO 45154 West side QEH carbonate nodule x x x x x x x 1-3 25 - 40 x x x A6 DINO 45146 East side QEH carbonate mudstone nodule x x x x ? x x 3-5 1-2 ~8 40 - 112 angular - subround x x x x x x ? A7 DINO 45149 West side QEH carbonate mudstone nodule x x x rare x x x x x x 12-15 2-4 80 5 - 30 to 170 angular - round x x x x x x x A8 DINO 45152 West side QEH carbonate mudstone nodule x x x x 10-15 26 - 52 169 - 247 angular - subround x x x x x A9 DINO 45158 East side QEH carbonate mudstone nodule x x x ? x x x 2-3 14 -80 x x x x x A10 DINO 45159 East side QEH carbonate mudstone nodule x x x ~3 3 - 4 40 - 62 60 - 220 450 angular - subround x x A11 DINO 45161 East side QEH carbonate mudstone nodule x x x x x ~40 to 360 ~40 to 275 x x x x x x x A12 DINO 45162 Camp Draw carbonate mudstone nodule x x x x x x 1-3 135 A13 DINO 45156 West side QEH limestone Bed X x x x x ~1 13 - 180 x x x x x x A14 DINO 45163 Camp Draw limestone Bed x x x x x 0 15 - 40 x x clasts A15 DINO 45164 East side QEH limestone Bed x x 3-5 10 - 115 x x x x x x A16 DINO 45144 East side QEH limestone Bed x x x x x x <1 x clasts x A17 DINO 45155 West side QEH limestone Bed x x x ~3 ~6 5 - 25 x x A18 DINO 45157 West side QEH limestone Bed x x x ? x x x <1 30 - 90 x x x x x ? A19 DINO 45160 East side QEH limestone Bed x x ? x 0-30 1.5- 2 4 - 10 60 x x x x x A20 DINO 45710 East side QEH limestone Bed x x x x x x x x x <1 5 - 45 angular - subround x clasts x x x x A21 DINO 45711 East side QEH limestone Bed x x x x x x x 7-10 25 - 90 angular - subround clasts x x