PI-39 Commonly Asked Questions About Utah's Great Salt Lake and Ancient Lake Bonneville
What is the origin of the Great Salt Lake?
After the Lake Bonneville flood, the Great Basin gradually became warmer and drier. Lake Bonneville began to shrink due to increased evaporation. Today's Great Salt Lake is a large remnant of Lake Bonneville, and occupies the lowest depression in the Great Basin. The size, shape, and location of this depression have been controlled by Basin and Range faulting. Subsidence within the depression, caused by downfaulting, has accommodated deposition of as much as 12,000 feet of sediment carried into the lake by its tributaries. It has also allowed the lake to remain in a relatively constant position. Other relics of Lake Bonneville are Utah Lake, Sevier Lake, and the Great Salt Lake Desert containing the famous Bonneville Salt Flats.
Who discovered Great Salt Lake?
The Spanish missionary explorers Dominguez and Escalante learned of Great Salt Lake from the Native Americans in 1776, but they never actually saw it. The first white person known to have visited the lake was Jim Bridger in 1825. Other fur trappers, such as Etienne Provost, may have beaten Bridger to its shores, but there is no proof of this. The first scientific examination of the lake was undertaken in 1843 by John C. Fremont; this expedition included the legendary Kit Carson. A cross, carved into a rock near the summit of Fremont Island, reportedly by Carson, can still be seen today.
Why is the Great Salt Lake salty?
Much of the salt now contained in the Great Salt Lake was originally in the water of Lake Bonneville. Even though Lake Bonneville was fairly fresh, it contained salt that concentrated as its water evaporated. A small amount of dissolved salts, leached from the soil and rocks, is deposited in Great Salt Lake every year by rivers that flow into the lake. About two million tons of dissolved salts enter the lake each year by this means.
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Where does the Great Salt Lake get its water, and where does the water go?
Great Salt Lake receives water from four main rivers and numerous small streams (66 percent), direct precipitation into the lake (31 percent), and from ground water (3 percent). The total average annual inflow to the lake is about 2.9 million acre feet of water.
The main rivers entering the lake are the Bear River from the north, the Weber and Ogden Rivers from the east, and the Jordan River from the south. The drainage basin of the lake covers an area of about 21,500 square miles.
The Great Salt Lake is a terminal lake because it has no surface outlet (rivers flowing from it). Water is lost from the lake mostly through evaporation. Evaporation rates are highest during the hot summer months and lowest during the winter. An average of about 2.9 million acre feet of water evaporates from the lake annually. When inflow equals evaporation, the level of the lake remains constant. If inflow is greater or less than evaporation, the level of the lake will rise or fall, respectively.
