The Badlands Fossil Beds

The Badlands of South Dakota form one of the richest fossil beds in the world, and the sedimentary layers exposed by erosion contain some of the most complete and well-preserved records of prehistoric mammal evolution found anywhere on earth. Fossils of ancient horses, three-toed rhinoceroses, saber-toothed cats, and giant pig-like creatures called entelodonts have been excavated from the White River Badlands since the 1840s. The American Museum of Natural History and other major institutions have mounted expeditions to the Badlands for over 150 years.

Source: Wikipedia