Badlands National Park is a national park in southwestern South Dakota that protects 242,756 acres of sharply eroded buttes, pinnacles, and spires blended with the largest undisturbed mixed grass prairie in the United States. The Badlands Wilderness protects 64,144 acres (25,958 ha) of the park as a designated wilderness area and is the site of the reintroduction of the black-footed ferret, the most endangered land mammal in North America..Wikipedia .