Lake Bonneville's birth and development were under way about 25,000 years ago. The climate associated with the most recent major ice age filled the lake to approximately 300 feet above the present Great Salt Lake elevation at what is now known as the Stansbury Level. This lake covered approximately 9,300 square miles and its shorelines stand out clearly above the oil refineries near the State Capitol, by the Kennecott Smelter, and immediately east of Wendover.
The lake then resumed its rise until by about 15,000 years ago it reached the lowest pass out of the Bonneville Basin and flowed into the Snake River drainage.
This lake level, the Bonneville Level, was controlled by the height of the pass near Red Rock Pass, at approximately a 5,090-foot elevation. The immense lake, with a surface area of 19,800 square miles, left shorelines traces for over 2,000 miles. Its relatively fresh waters supported a diverse biota including many species of fish. This highest shoreline of Lake Bonneville and its beaches now forms a high bench for residential developments of the Wasatch Front communities. The steeper terrain above this shoreline generally has not been developed. Virtually all of the Wasatch Front area that now is home to most of the residents and industries of Utah was below the waters of Lake Bonneville at this time.