Lake Bonneville was a prehistoric pluvial lake that covered much of the eastern part 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. (Its counterpart Lake Lahontan occupied much of northwestern Nevada while extending into California and Oregon.) Formed about 32,000 years ago, Lake Bonneville existed until about 14,500 years ago, when a large portion of the lake was released through the Red Rock Pass in Idaho. Following the Bonneville Flood, as the release is now known, the lake receded to a level called the Provo Level. Many of the unique geological characteristics of the Great Basin are due to the effects of the lake.