How did the Bonneville Salt Flats form?
When Lake Bonneville was at its highest level approximately 17,000 years ago, the water exceeded 1,000 feet deep over the salt flats. Evidence of this depth is seen as horizontal terraces and escarpments on the sides of the nearby Silver Island Mountains. As Lake Bonneville receded, evaporation left large concentrations of dissolved minerals deposited in surrounding soils. These minerals include potash, which is commercially used as fertilizer and halite (table salt). The Bonneville Salt Flats are comprised of approximately 90% salt.
Today, shallow ground water flows from the surrounding watershed, picks up dissolved minerals along the way, and percolates up to Salt Flats’ surface. When temperatures rise in the late spring and summer months, the salty water rapidly evaporates in the heat and the minerals are left behind to form the salt crust. During the cooler months (November to May), this groundwater floods the Salt Flats several inches deep. When temperatures rise in late spring and summer, the salty water rapidly evaporates in the heat, and minerals are left behind to form new salt crust. Wind, periodic rainstorms, and regional climate also play an important part in changing salt crust conditions throughout each year. The stratified layers that form the salt flats are almost 5 feet thick near the center and only an inch or two at the outer edges. The Salt Flats are just over 46 square miles in size (30,000 acres) which equates to about 147 million tons, or 99 million cubic yards, of salt!
Where did the name come from?
In 1833, explorer Joseph R. Walker mapped around the Great Salt Lake. He also crossed the northern perimeter of the Salt Flats while working for Captain Benjamin L.E. Bonneville. At that time it was common for people to name significant landmarks after their employers. It is from Captain Bonneville that the salt flats and ancient lake derive their name. There is no known historical record of Bonneville himself ever seeing the Salt Flats or the Great Salt Lake.
Researchers have determined that primitive people lived there more than 10,000 years ago at nearby Danger Cave. How did they live? Did the receding Lake Bonneville provide them with food and water? These questions have only been partially answered by archaeologists.
Trapper and frontiersman Jedediah Smith crossed the Salt Flats while returning to Utah from an expedition to California in 1827. John C. Fremont and his U.S. government-sponsored expedition crossed through the heart of the salt flats in 1845 while trying to find a shorter overland route to the Pacific Ocean. The next year Fremont's route across the flats would come to be known as the Hastings Cutoff as part of the California Trail. Promoted by Lansford Hastings as a faster, easier route to California, Hastings Cuttoff proved to be just the opposite for the Donner-Reed party of 1846. What contributing to the party’s infamous winter survival was the delay the emigrants experienced while crossing the Salt Flats when their wagons became mired in the mud found just below the salt crust. Artifacts from the Donner-Reed Party and other emigrants that crossed the trail are on display in the Donner-Reed Museum in Grantsville.
Bureau of Land Management
Salt Lake Field Office
2370 South 2300 West
Salt Lake City, Utah 84119