Question: In what region of the state which contains the county that includes Riverdale Township are the badlands located?

full_context: Document 1: Sioux Center, Iowa: Sioux Center is a city in Sioux County, Iowa, United States with a population of 7,048 (2010 census). Sioux Center is notable for its recent population boom, Dutch heritage, and agribusiness.
Document 2: Elm Creek Township, Buffalo County, Nebraska: Elm Creek Township is one of twenty-six townships in Buffalo County, Nebraska. The population was 1,241 at the 2000 census. A 2006 estimate placed the township's population at 1,202.
Document 3: Badlands National Park: Authorized as Badlands National Monument on March 4, 1929, it was not established until January 25, 1939. It was redesignated a national park on November 10, 1978.
Document 4: Corson County, South Dakota: The county is encompassed within the Standing Rock Indian Reservation, which extends into North Dakota. The Lakota people reside primarily in the South Dakota part of the reservation; the Yanktonai and Dakota live in that part in North Dakota. The Grand River, a tributary of the Missouri River, runs through the reservation.
Document 5: Custer, South Dakota: Custer is a city in Custer County, South Dakota, United States. The population was 1,987 at the 2010 census. It is the county seat of Custer County.
Document 6: Oklahoma: With 39,000 acres (158 km2), the Tallgrass Prairie Preserve in north-central Oklahoma is the largest protected area of tallgrass prairie in the world and is part of an ecosystem that encompasses only 10 percent of its former land area, once covering 14 states. In addition, the Black Kettle National Grassland covers 31,300 acres (127 km2) of prairie in southwestern Oklahoma. The Wichita Mountains Wildlife Refuge is the oldest and largest of nine national wildlife refuges in the state and was founded in 1901, encompassing 59,020 acres (238.8 km2).
Document 7: Rapid City, South Dakota: Rapid City (Lakota: Mni Lúzahaŋ Otȟúŋwahe; ``Swift Water City '') is the second most populous city in South Dakota and the county seat of Pennington County. Named after Rapid Creek, on which the city is established, it is set against the eastern slope of the Black Hills mountain range. The population was 67,956 as of the 2010 Census.
Document 8: Rusco Township, Buffalo County, Nebraska: Rusco Township is one of twenty-six townships in Buffalo County, Nebraska, United States. The population was 233 at the 2000 census. A 2006 estimate placed the township's population at 230.
Document 9: Badlands National Park: Badlands National Park (Lakota: Makȟóšiča) is a national park of the United States located in southwestern South Dakota. It protects 242,756 acres (379.306 sq mi; 98,240 ha) of sharply eroded buttes, pinnacles, and spires blended with the largest undisturbed mixed grass prairie in the United States. The park is managed by the National Park Service.
Document 10: Scott Township, Buffalo County, Nebraska: Scott Township is one of twenty-six townships in Buffalo County, Nebraska, United States. The population was 98 at the 2000 census. A 2006 estimate placed the township's population at 96.
Document 11: Theodore Roosevelt National Park: Theodore Roosevelt National Park is a United States National Park comprising three geographically separated areas of badlands in western North Dakota. The park was named for U.S. President Theodore Roosevelt. The park covers 70,446 acres (110.072 sq mi; 28,508 ha; 285.08 km) of land in three sections: the North Unit, the South Unit, and the Elkhorn Ranch Unit.
Document 12: Shelton Township, Buffalo County, Nebraska: Shelton Township is one of twenty-six townships in Buffalo County, Nebraska, United States. The population was 1,497 at the 2000 census. A 2006 estimate placed the township's population at 1,475.
Document 13: Buffalo County, South Dakota: In 2010, the center of population of South Dakota was located in eastern Buffalo County. The Crow Creek Indian Reservation, inhabited by the Crow Creek Sioux Tribe makes up the majority of Buffalo County.
Document 14: Needles (Black Hills): The Needles of the Black Hills of South Dakota are a region of eroded granite pillars, towers, and spires within Custer State Park. Popular with rock climbers and tourists alike, the Needles are accessed from the Needles Highway, which is a part of Sylvan Lake Road (SD 87/89). The Cathedral Spires and Limber Pine Natural Area, a 637-acre portion of the Needles containing six ridges of pillars as well as a disjunct stand of limber pine, was designated a National Natural Landmark in 1976.
Document 15: Riverdale Township, Buffalo County, Nebraska: Riverdale Township is one of twenty-six townships in Buffalo County, Nebraska, United States. The population was 1,939 at the 2000 census. A 2006 estimate placed the township's population at 1,908.
ground_truth: southwestern South Dakota
sub_queries: Riverdale Township >> located in the administrative territorial entity Answer: Buffalo County
Buffalo County >> located in the administrative territorial entity Answer: South Dakota
where are the badlands located in South Dakota Answer: southwestern South Dakota