The eastern two-fifths of South Dakota is prairie, belonging to the Central Lowlands. The western three-fifths falls within the Missouri Plateau, part of the Great Plains region; the High Plains extend into the southern fringes of the state. The Black Hills, an extension of the Rocky Mountains, occupy the southern half of the state's western border; the mountains, which tower about 4,000 ft (1,200 m) over the neighboring plains, include Harney Peak, at 7,242 ft (2,209 m) the highest point in the state. East of the southern Black Hills are the Badlands, a barren, eroded region with extensive fossil deposits. South Dakota's lowest elevation, 966 ft (295 m), is at Big Stone Lake, in the northeastern corner. Flowing south and southeast, the Missouri River cuts a huge swath through the heart of South Dakota before forming part of the southeastern boundary. Tributaries of the Missouri include the Grand, Cheyenne, Bad, Moreau, and White rivers in the west and the James, Vermillion, and Big Sioux in the east. The Missouri River itself is controlled by four massive dams—Gavins Point, Ft. Randall, Big Bend, and Oahe—which provide water for irrigation, flood control, and hydroelectric power. Major lakes in the state include Traverse, Big Stone, Lewis and Clark, Francis Case, and Oahe.