stretch of barren salt flats covering about 100 square miles (260 square km) in Tooele county, northwestern Utah, U.S. The flats, part of the Great Salt Lake Desert, are a remnant of the bed of an ancient lake formed about 30,000 years ago late in the Pleistocene Epoch and named for B.-L.-E. de Bonneville (Bonneville, Benjamin-Louis-Eulalie de), an explorer and fur trader. The site of Bonneville Speedway, the extremely level, smooth flats are as solid as concrete by the summer's end and are ideally suited for speed trials; several world automobile and motorcycle speed and endurance records have been established there since 1935.