Abstract The Quaternary record of the Uinta Mountains of northeastern Utah has been studied extensively over the past decade, improving our understanding of the Pleistocene glacial record and fluvial system evolution in a previously understudied part of the Rocky Mountains. Glacial geomorphology throughout the Uintas has been mapped in detail and interpreted with reference to other well-studied localities in the region. In addition, studies in Browns Park and Little Hole in the northeastern part of the range have provided information about paleoflooding, canyon cutting, and integration of the Green River over the Uinta Mountain uplift. Notable contributions of these studies include (1) constraints on the timing of the local last glacial maximum in the southwestern Uintas based on cosmogenic surface exposure dating, (2) insight into the relationship between ice dynamics and bedrock structure on the northern side of the range, and (3) quantification of Quaternary incision rates along the Green River. This guide describes a circumnavigation of the Uintas, visiting particularly well-documented sites on the north and south flanks of the range and along the Green River at the eastern end.

Abstract The Neoproterozoic Uinta Mountain Group is undergoing a new phase of stratigraphic and paleontologic research toward understanding the paleoenvironments, paleoecology, correlation across the range and the region, paleogeography, basin type, and tectonic setting. Mapping, measured sections, sedimentology, paleontology, U-Pb geochronology, and C-isotope geochemistry have resulted in the further characterization and genetic understanding of the western and eastern Uinta Mountain Group . The Red Pine Shale in the western Uinta Mountain Group and the undivided clastic strata in the eastern Uinta Mountain Group have been a focus of this research, as they are relatively unstudied. Reevaluation of the other units is also underway. The Red Pine Shale is a thick, organic-rich, fossiliferous unit that represents a restricted environment in a marine deltaic setting. The units below the Red Pine Shale are dominantly sandstone and orthoquartzite, and represent a fluviomarine setting. In the eastern Uinta Mountain Group, the undivided clastic strata are subdivided into three informal units due to a mappable 50–70-m-thick shale interval. These strata represent a braided fluvial system with flow to the southwest interrupted by a transgressing shoreline. Correlation between the eastern and western Uinta Mountain Group strata is not complete, yet distinctive shale units in the west and east may be correlative, and one of the latter has been dated (≤770 Ma). Regional correlation with the 770–742 Ma Chuar Group suggests the Red Pine Shale may also be ca. 740 Ma, and correlation with the undated Big Cottonwood Formation and the Pahrump Group are also likely based upon C-isotope, fossil, and provenance similarities. This field trip will examine these strata and consider the hypothesis of a ca. 770–740 Ma regional seaway, fed by large braided rivers, flooding intracratonic rift basins and recording the first of three phases of rifting prior to the development of the Cordilleran miogeocline .