Fossil Butte National Monument is a United States National Monument managed by the National Park Service, located 15 miles (24 km) west of Kemmerer, Wyoming, United States. It centers on an assemblage of Eocene Epoch (56 to 34 million years ago) animal and plant fossils associated with Fossil Lake—the smallest lake of the three great lakes which were then present in what are now Wyoming, Utah, and Colorado. The other two lakes were and . Fossil Butte National Monument was established as a national monument on October 23, 1972.