South Dakota's largest industry is agriculture, producing crops like wheat, corn, and soybeans, as well as livestock. The bison population was decimated by settlers but has since rebounded to 250,000. Gold was discovered in the Black Hills in 1874, spurring a boom and the founding of towns like Deadwood. Mount Rushmore was carved between 1927-1941 to feature four U.S. presidents. South Dakota became the 40th state in 1889 after being part of Dakota Territory.