Great Salt Lake is the latest in a long succession of often more extensive lakes that have occupied the basin of Great Salt Lake over the past several million years. The sediments deposited in the lake and features formed by the waters of these successive lakes provide impressive geologic evidence about the past, and also provide sand and gravel for construction materials, benches and flat spaces for urban development, and scenic horizontal "bathtub rings" along the surrounding foothills. Lake Bonneville, the most recent larger lake, formed the most striking of these beaches, deltas, spits, and wave-cut cliffs that are as high as a thousand feet above the present Great Salt Lake.
Because the basin of Great Salt Lake has no outlet, water leaves only through evaporation. The temperature and the surface area of a closed-basin lake primarily control the amount of water evaporated from the lake. When precipitation is high, more water is added to the lake by direct precipitation on the lake and from rivers and streams flowing into the lake than is evaporated from the lake; the result is that the lake rises and expands across a larger area of the basin. The surface area of the lake continues to increase until the amount of water evaporated equals the total amount of water entering the lake. During the last 10,000 years the level of Great Salt Lake has gone through many cycles but the lake has not risen more than about twenty feet higher than its average historic elevation of 4,202 feet above sea level. When the climate of the region becomes dramatically cooler and wetter, such as during ice ages, the lake in the Great Salt Lake basin rises to much higher levels. One such rise occurred about 140,000 years ago when the lake in the basin rose to an elevation about 700 feet above the current level of Great Salt Lake, and again about 65,000 years ago when the lake rose about half that high. The highest and most recent lake high lake cycle began about 25,000 years and produced Lake Bonneville, a huge lake over 1,000 feet deep that extended over most of northwestern Utah and into Nevada and Idaho.