The Geological History of Fossil Butte National Monument and Fossil Basin

The report reconstructs the Eocene geological and biological history of an intermontane lake system in southwestern Wyoming, tracing sedimentary sequences and stratigraphy from older formations through the Green River and related units. It interprets depositional environments—shallow shore, deeper chemical-lake deposits, and fluvial inputs—and outlines structural evolution of the basin. Detailed paleontological inventories document abundant fossil fish, diverse plants, invertebrates, birds, reptiles, amphibians, and mammals, with discussion of preservational processes, paleoecology, and taphonomy that explain mass mortalities and exceptional fossil preservation. The work concludes with Quaternary modifications, glossary, references, and maps supporting the regional synthesis.