The Saints & Sinners Quarry preserves the only known vertebrate body fossils in the Nugget Sandstone and the most diverse fauna known from the Nugget-Navajo-Aztec erg system. The fauna includes eight genera and >18,000 bone and bone fragments assignable to >76 individuals, including theropods, sphenosuchians, sphenodontians, drepanosaurs, procolophonids, and a dimorphodontid pterosaur. Cycadeoid fronds are the only plant fossils. There are two depositional environments at the site – dune and interdune, each consisting of two or more faces. The dune facies are (1) Trough Cross-Stratified Sandstone (TCS) representing dry dunes, and (2) Massive and Bioturbated Dunes (MBD) representing bioturbated, damp dunes. The interdune facies are (1) Wavy Sandstone (WSS) representing wet and damp flats with biofilms and tridactyl tracks, (2) Green Clays and Silts (GCS) representing quiet lacustrine waters, (3) Planar Laminated Sandstone (PLS) representing lacustrine dust and sand storm deposits which grade laterally into (4) Massive Bone Bed (MBB) shoreline deposits. The vertical and lateral relationships of the dune and interdune facies suggests that an interdune flat developed (WSS facies) likely by deflation of dunes down to, or near to, the water table. As the water table rose, a shallow lake developed (GCS facies) and trapped wind-blown sediment during sand storms (PLS Facies). The taxonomically diverse vertebrate fauna suggest a mass die-off occurred, likely due to drought. The carcasses and bones were buried by three distinct depositional events, each a bone bed (MBB facies) - separated by very thin clays (GCS facies). Thereafter the water table dropped resulting in several cm-scale sandstone beds with tridactyl tracks (WSS facies). Then migrating dunes buried the interdune flat. These dunes hosted burrowing invertebrates for a moderate time resulting in the destruction of nearly all primary sedimentary structures (MBD facies). Ultimately, as the area dried further, more dunes migrated over these bioturbated surfaces and the area returned to dune field conditions (TCS facies). The Saints & Sinners site indicates that a previously unrecognized, remarkably diverse vertebrate fauna thrived in wet interdunes of western North America's Late Triassic erg system. A massive-die-off, likely due to a drought, provided a wealth of carcasses and their bones. The dynamic shoreline representing the interface of dunes and standing water provided favorable conditions for rapid burial of small carcasses and the disarticulated bones of larger individuals.

Upper Triassic strata that lie between the Chinle Formation and Nugget Sandstone along the south flank of the Uinta Mountains in northeastern Utah are distinctive. In the past, these rocks have been lumped together with the overlying or underlying units. These strata are equivalent to the Bell Springs Member of the Nugget Sandstone as defined in Wyoming and perhaps to the Rock Point Formation of the Chinle Formation near the Four Corners region. In this study, these rocks will be called the Bell Springs Formation following the usage of Lucas (1993) in Wyoming. The unit is regionally mappable in northeastern Utah, and is the sedimentologic transition from the fluvial-lacustrine environment of the Chinle Formation to the eolian depositional environment of the Nugget Sandstone. The Bell Springs Formation is comprised of interbedded fine- to medium-grained sandstone and siltstone, as well as planar laminated mudstone. The unit varies from planar laminated sandstone with abundant ripple marks, to cross-bedded sandstone that contains scoured channels filled with mudstone or sandstone. The mudstone beds are commonly mottled and contain desiccation cracks while both the mudstone and sandstone beds have rip-up clasts, occasional bioturbation, and small salt crystal casts. The thinly bedded mudstone and siltstone beds are purple to red to brown, and the sandstone beds vary in color from red to brown to orange or tan with green and gray mottling. The ripple structures with mud drapes indicate fluctuating deposition in low energy water. The presence of desiccation cracks, plant root traces, small eolian sand dunes, gypsum casts, crinkly algal mat beds, and bioturbation indicate intermittent subaerial exposure. Fluvial deposits by meandering streams, including point bar, levee, and splay deposits comprise a large part of this formation. Rocks of the Bell Springs Formation have previously been interpreted as either tidal flat or fluvial/lacustrine deposits. A tidal flat environment certainly may produce some of the features found in these deposits, such as, alternating erosion and deposition of interfingering channels and scours with rip-up clasts, ripples, flaser bedding, desiccation cracks, and bioturbation; however, these rocks lack some of the most important characteristics of tidal flat deposits such as herringbone-cross-stratification, general fining upward successions, and regionally associated sediments that would typically be found in shallow marine environments. We conclude that the sedimentary characteristics and regional setting of these rocks fit best with a fluvial environment interpreted as a meandering system being deposited on a broad floodplain in an arid to semi-arid climate. This depositional environment existed between the expanding Nugget Sandstone erg and the shrinking Chinle Formation as desertification increased during the Late Triassic and Early Jurassic in what is now the western United States. This study not only helps solidify the understanding of the depositional history of these strata, it also clarifies the nomenclature of these formations for future mapping and research.

Nomenclature for the Upper Triassic and Lower Jurassic strata along the south flank of the Uinta Mountains has been somewhat confusing because of the position of the study area between southern Wyoming, where one set of names is used, and central/southern Utah where a different set of formation names is used. The Nugget Sandstone or Glen Canyon Sandstone of the eastern Uinta Mountains overlies the Upper Triassic Popo Agie or Chinle Formation. The nature of the contact between these two formations is unclear both in stratigraphic location and conformability. The Chinle Formation consists, in ascending order, of the Gartra Member, the purple unit, the ocher unit, and the upper red unit. The overlying Nugget Sandstone consists of two members, the lower Bell Springs Member and the overlying unnamed cross-bedded member, typically believed to be Navajo Sandstone equivalent. These two units of the Nugget Sandstone are thought to represent the Glen Canyon Group of the Colorado Plateau, although no obvious Wingate or Kayenta Formation equivalents have been recognized. The Bell Springs Member contains abundant fine-grained, ripple-laminated sandstones, red and green mudstones, occasional mudcracks and salt casts, evidence of burrowing and exposure, and some medium- to coarse-grained sandstones with small-scale (30-40 cm high) cross-beds. This member was deposited in a marine tidal flat environment, quite different from the mainly eolian environment of the rest of the Nugget Sandstone. The Bell Springs Member appears to be entirely Upper Triassic, based upon dinosaur tracks, while the upper windblown unit's age is unknown, but probably straddles the Triassic-Jurassic boundary. During mapping in the Donkey Flat, Steinaker Reservoir, Dry Fork, and Lake Mountain quadrangles, the Bell Springs Member of the Nugget Sandstone was mapped as a separate unit.