Badlands National Park is a national park of the United States in southwestern South Dakota. The park protects 242,756 acres of sharply eroded buttes and pinnacles, along with the largest undisturbed mixed grass prairie in the United States. The National Park Service manages the park, with the South Unit being co-managed with the Oglala Lakota tr…Badlands National Park is a national park of the United States in southwestern South Dakota. The park protects 242,756 acres of sharply eroded buttes and pinnacles, along with the largest undisturbed mixed grass prairie in the United States. The National Park Service manages the park, with the South Unit being co-managed with the Oglala Lakota tribe.