During the cooler months of the year (November to May), evaporation slows down and the ground water floods the Salt Flats several inches deep. 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. Today, ground water slowly flows towards the Salt Flats from the surrounding watershed, picks up dissolved minerals along the way, and percolates up to the surface via a shallow brine aquifer. The area is comprised of approximately 90% common table salt. Total salt crust volume has been estimated at 147 million tons or 99 million cubic yards of salt. Near the center of the salt, the crust is almost 5 feet thick in places, with the depth tapering off to less than 1 inch as you get to the edges. Potassium and magnesium are also present in smaller concentrations. These minerals include gypsum (commercially used to make household wallboard) and halite (common table salt).

When this large amount of fresh water slowly disappeared over time, large concentrations of dissolved minerals were deposited in the soils that form the watershed for the Bonneville Salt Flats. Lake Bonneville covered approximately 1/3 of Utah and was almost 1000 feet deep in the area of the Salt Flats. The formation of the Salt Flats began at the end of the last Ice Age, when the waters of ancient Lake Bonneville began to recede.

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