State, north-central U.S. Area: 77,117 sq mi (199,732 sq km). Pop. (2009 est.): 812,383. Capital: Pierre. South Dakota is bordered on the north by North Dakota, on the east by Minnesota and Iowa, on the south by Nebraska, and on the west by Wyoming and Montana. The state has three main regionsthe eastern prairie; the central Great Plains, which contain the Badlands; and the Black Hills to the west. The Missouri River bisects it from north to south. The French explored the area in the 18th century and sold it to the U.S. as part of the Louisiana Purchase in 1803. The Lewis and Clark Expedition spent about seven weeks there in 1804. The Dakota Territory was created in 1861, but settlement was sparse until the Black Hills gold rush of 1875–76 swelled the population. Intermittent wars between the Sioux and settlers occurred until the massacre at Wounded Knee in 1890. South Dakota became the 40th U.S. state in 1889. Farming and related industries form the state's economic base. It is a leader in cattle and hog production, and its main crops are grains. Tourism is a major industry; attractions include Mount Rushmore, Wind Cave National Park, Badlands National Park, and Jewel Cave National Monument.