Badlands National Park is an American national park located in southwestern South Dakota. The park protects 242,756 acres (379.306 sq mi; 98,240 ha) of sharply eroded buttes and pinnacles, along with the largest undisturbed mixed grass prairie in the United States. Authorized as Badlands National Monument on March 4, 1929, it was not established until January 25, 1939. Badlands was redesignated a national park on November 10, 1978. Under the Mission 66 plan, the Ben Reifel Visitor Center was constructed for the monument in 1957–58. The park also administers the nearby Minuteman Missile National Historic Site. Movies such as Dances with Wolves (1990) and Thunderheart (1992) were partially filmed in Badlands National Park.