This study investigates the depositional environment, sedimentological dynamics, and tectonic influences 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 sandstone 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 depositional setting. This uplift restricted accommodation, triggering a transition in fluvial systems from single-threaded sinuous channels to multithreaded braided rivers with frequent avulsions. The interconnected nature of these braided channels over time reshaped sediment distribution patterns, producing the distinctive characteristics of the Quarry Sandstone
