Pronghorn Antelope on Wildlife Loop Road, Custer State Park

The pronghorn is North America's fastest land mammal, capable of sustained speeds near 55 miles per hour, an adaptation from Pleistocene-era predators long since extinct. Custer State Park, established in 1919 in the Black Hills of South Dakota, maintains a resident pronghorn herd alongside its bison, elk, and mule deer populations. The park's 18-mile Wildlife Loop Road was built specifically to let visitors drive through open grassland habitat where these animals roam freely. Unlike true antelope, pronghorn are the sole surviving member of the family Antilocapridae, and both sexes can grow horns, though the male's are larger and hooked.