This is a small, fossil-oriented park. It is known mainly for it’s mammal fossils from the Miocene Epoch, including “beardogs”, gazelle-camels, horse relatives with claws, early rhinos and “terrible hogs” with bone-crushing teeth. But it is perhaps best-known for a smaller mammal: a relative of beavers that made spiral-shaped burrows called “devil’s corkscrews” or “daemonelix”. Near the entrance of the park, there is a one-mile long trail where you can see these fossilized burrows where they were discovered. At the visitor center, there are museum-like displays of the creatures found in the park’s rocks.
During the Miocene Epoch, "today's Great Plains region was drying out. Flowering plants proliferated, and the abundant animals, including birds, responded to a new food source: grasslands that replaced forest and jungle. Although slightly different anatomically, some of these creatures resemble those of today. Others of these long extinct animals that succeeded the dinosaurs came in bizarre shapes and sizes that influenced people's imagined monsters of yesteryear."