Fossil Butte National Monument

Fossil Butte National Monument in southwestern Wyoming is world renowned for its large and unusual concentration of fossilized fish and other life forms, dating back to the Paleocene and Eocene epochs, about 40-65 million years ago. The region, known as Fossil Basin, contained three ancient lakes: Lake Gosiute, Lake Uinta, and Fossil Lake. The lake sediments turned into rock layers known as the Green River Formation, which preserves, under about 35 feet of laminated shale and calcite, the most noteworthy U.S. accumulation of freshwater fossil fish. Discovered in 1856. It was established as a monument in 1972.