of western South Dakota have more in common with the West than the Midwest. South Dakota has a total area of , making the state the 17th largest in the Union. Black Elk Peak, formerly named Harney Peak, with an elevation of , is the state's highest point, while the shoreline of Big Stone Lake is the lowest, with an elevation of . South Dakota is bordered to the north by North Dakota; to the south by Nebraska; to the east by Iowa and Minnesota; and to the west by Wyoming and Montana. The geographical center of the U.S. is west of Castle Rock in Butte County. The North American continental pole of inaccessibility is between Allen and Kyle, from the nearest coastline. The Missouri River is the largest and longest river in the state. Other major South Dakota rivers include the Cheyenne, James, Big Sioux, and White Rivers. Eastern South Dakota has many natural lakes, mostly created by periods of glaciation. Additionally, dams on the Missouri River create four large reservoirs: Lake Oahe, Lake Sharpe, Lake Francis Case, and Lewis and Clark Lake. Regions and geology South Dakota can generally be divided into three regions: eastern South Dakota, western South Dakota, and the Black Hills. The Missouri River serves as a boundary in terms of geographic, social, and political differences between eastern and western South Dakota. The geography of the Black Hills, long considered sacred by Native Americans, differs from its surroundings to such an extent it can be considered separate from the rest of western South Dakota. At times the Black Hills are combined with the rest of western South Dakota, and people often refer to the resulting two regions divided by the Missouri River as West River and East River. Eastern South Dakota generally features higher precipitation and lower topography than the western part of the state. Smaller geographic regions of this area include the Coteau des Prairies, the Dissected Till Plains, and the James River Valley. The Coteau des Prairies is a plateau bordered on the east by the Minnesota River Valley and on the west by the James River Basin. Further west, the James River Basin is mostly low, flat, highly eroded land, following the flow of the James River through South Dakota from north to south. The Dissected Till Plains, an area of rolling hills and fertile soil that covers much of Iowa and