Fossil Butte national Monument
Fossils from Fossil Butte National Monument are from the Eocene epoch of the Tertiary period in the Cenozoic Era. The Eocene epoch was about 33.7 to 54.8 million years ago. These fossils were deposited in what is known as "Fossil Lake," a huge lake located here during that time. Fossil Butte has some of the best preserved fossils from the Tertiary period.