South Dakota shows some of the earliest geologic history of the continent in the rock formations of the ancient Black Hills and in the Badlands. In the area between the White River and the south fork of the Cheyenne, the Badlands display in their deeply eroded clay gullies not only colorful, fantastic shapes, but also a wealth of easily accessible marine and land fossils (the Badlands National Monument preserves the area for its startling scenery and geologic interest). From east to west the state rises some 6,000 ft (1,829 m) to Harney Peak (7,242 ft/2,207 m) in the Black Hills, highest point in the United States E of the Rockies.
Through the center of the state the Missouri River cuts a wide valley southward; other principal rivers include the James and the Big Sioux to the east, and the Cheyenne, the Belle Fourche, the Moreau, the Grand River, and the White River to the west. The whole of South Dakota has a continental climate; summer brings a succession of hot, cloudless days, and in winter blizzards sweep across bare hillsides, filling the coulees with deep snow. The average annual rainfall is low, and declines from east to west across the state, and in years of drought summer winds blow away acres of top soil in "black blizzards."
Among the state's attractions are Badlands and Wind Cave national parks, Jewel Cave National Monument, and the famous gigantic carvings of the Mount Rushmore National Memorial (see National Parks and Monuments, table). Pierre is the capital; the largest cities are Sioux Falls and Rapid City.