Lake Bonneville was a large ancient Pleistocene-era lake that existed about 32,000 to 14,000 years ago. For thousands of years, Ancient Lake Bonneville was contained by mountains acting as natural dams, occupying the lowest closed depression in the eastern Great Basin. The largest area covered by the lake was more than 20,000 square miles, about 325 miles long, 134 miles wide, with depths of just over 1,000 feet. During the existence of Ancient Lake Bonneville, the climate was somewhat wetter and colder than now. The lake was a freshwater lake, its sources coming from direct precipitation and melting glaciers. Once captured, the water remained in the lake, except for evaporation. As the lake expanded in size, it gradually spread over much of Utah and into Nevada and Idaho. At the edges of Ancient Lake Bonneville, waves and erosion cur shorelines in the naked rock, leaving behind terraces to mark its water levels. The shorelines are identified by a shelf or bench protruding from the mountainside, well above the valley floor. Four main terraces cut into the mountain rock can be observed. The Bonneville Terrace, Provo Terrace, and Stansbury Terrace each show the rise or fall of the lake surrounding West Wendover. The Stansbury shoreline is the oldest of these three terraces, dating over 30,000 years. The Bonneville Terrace is the highest, at just over 5,000 feet above sea level. Where you are standing now would be under approximately 530 feet of water. At this height, about 14,500 years ago, the lake broke through a natural earthen dam and spilled into a tributary of the Snake River at Red Rock Pass in southeast Idaho, discharging an immense volume of water which helped cut the Snake River. This event is known as the Bonneville Flood, which lowered the outlet and surface elevation of Ancient Lake Bonneville by over 350 feet. After the flood, Ancient Lake Bonneville carved out the Provo Shoreline Terrace of today, at just over 4,700 feet above sea level. Approximately 12,000 years ago, the level of Ancient Lake Bonneville fell sharply due to changes in the Great Basin climate. The fourth terrace, known as the Gilbert Terrace, was the last shoreline of the once great lake before retreating into what is today, the Great Salt Lake, located adjacent to Salt Lake City, Utah.

Great Salt Lake Desert

The Bonneville Salt Flats or the Great Salt Lake Desert was left behind when Ancient Lake Bonneville evaporated, leaving a vast concentration of salts and minerals. The flats are composed of potassium, magnesium, lithium, and sodium chloride (common table salt), ranging in thickness from less than one inch to six feet. The Salt Flats are one of the flattest areas on earth; the curvature of the earth can actually be observed from a viewpoint west of your current location. The 3,000-square-mile salt flats are 35 percent larger than any other salt bed worldwide. In the winter, a shallow later of standing water covers the surface, giving it a mirror-like affect. Wind combines with water to create the flat surface. Once the water has evaporated, a dry, hard, salt surface remains. The white surface is always cool du to the reflective nature of the salt. As the sun’s light and heat rise from the blinding-white surface, shimmering mirages appear. The purest salt is hard as concrete when dry and makes the world’s best racing surface. Known as the greatest speedway in the world, for nearly a century it has been used to set records of speed and endurance. In 1910, Ab Jenkins traveled 60 M.P.H. on a Yale Motorcycle. Sixty years later, Gary Gabelich, in the Blue Flame jet-powered rocket car, produced a top speed of 622.40 M.P.H., a speed that stands as the fastest documented time on Bonneville. Each year, racers from around the world come to Bonneville to take on the salt. This annual event has taken place every August for more than 60 years.

Benneville’s Name

In 1833, Joseph Reddeford Walker, explorer and frontiersman, mapped the area around the Great Salt Lake and crossed the northern perimeter of the flats while in the employ of Captain Benjamin E. Bonneville, and officer in the U.S. Army. Although it is unlikely that Bonneville himself ever visited here, Ancient Lake Bonneville and the salt flats derive their name from him.

Related Posts: