Abstract The Bridger Formation is located in the Green River basin in southwest Wyoming, and the Uinta and Duchesne River formations are located in the Uinta basin in Utah. These three rock units and their diverse fossil assemblages have great scientific importance and are also of historic interest to vertebrate paleontologists. Notably, they are also the stratotypes for the three middle Eocene North American Land Mammal “Ages,” the Bridgerian, Uintan, and Duchesnean, from oldest to youngest. The fossils and sediments of these formations provide a critically important record of biotic, environmental, and climatic history spanning ~10 million years (49–39 Ma). This article features a detailed field excursion through portions of the Green River and Uinta basins that focuses on locations of geologic, paleontologic, and historical interest. In support of the field excursion, we also provide a review of current knowledge of these formations with emphasis on lithostratigraphy, biochronology, depositional and paleoenvironmental history, and the history of scientific exploration.

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.