Lake Bonneville was a prehistoric lake which covered much of North America's Great Basin region. Most of the territory it covered was in present-day Utah, though parts of the lake extended into present-day Idaho and Nevada. Formed about 32,000 years ago, it existed until about 16,800 years ago, when most of the contents of the lake were released through the Red Rock Pass in Idaho.
At its peak, the freshwater lake covered over 20,000 square miles and was over 1000 feet deep in places. Many of the unique geological characteristics of the Great Basin are due to the effects of the lake.
The Great Salt Lake, the world's largest saltwater lake, is a remnant of the original Lake Bonneville. Parts of the old shoreline are still visible above Salt Lake City and elsewhere; appearance is that of a shelf or bench protruding from the mountainside, well above the valley floor.