Bonneville Salt Flats, desert area in Tooele co., NW Utah, c.14 mi (22.5 km) long and 7 mi (11.2 km) wide. The smooth salt surface of the Flats is ideal for auto racing, and several world land speed records have been set there. The Flats are part of Great Salt Lake Desert, NW Utah, the former bed of Lake Bonneville, whose area once covered c.19,500 sq mi (50,500 sq km). The lake expanded during the late Cenozoic era, then shrank rapidly at the end of the Pleistocene epoch. Six terraces indicate different lake levels. Great Salt Lake, Lake Sevier, and Utah Lake are remnants of Lake Bonneville, which was named for U.S. explorer Benjamin de Bonneville.