badlands, area of severe erosion, usually found in semiarid climates and characterized by countless gullies, steep ridges, and sparse vegetation. Badland topography is formed on poorly cemented sediments that have few deep-rooted plants because short, heavy showers sweep away surface soil and small plants. Depressions gradually deepen into gullies. The term badlands was first applied to the arid, dissected plateau region of SW South Dakota by Native Americans and fur trappers who found the area difficult to cross. South Dakota's Big Badlands, also known as the Badlands of the White River, are the world's best and most extensive (c.2,000 sq mi/5,180 sq km) example of this topography. Gullies have cut as deep as 500 ft (152 m) below the plateau's surface, and differences in rock type have created colorful and spectacular formations. The Big Badlands are famous for fossils of prehistoric animals. Badlands National Park, 242,756 acres (98,316 hectares), (authorized as a national monument in 1929, designated a national park in 1978) occupies most of the region. The park is noted for its scenery, its fossils of prehistoric animals, and its varied wildlife, including bison, bighorn sheep, deer, antelope, and prairie dogs. See National Parks and Monuments (table).