POPULAR GEOLOGY

Great Salt Lake & Lake Bonneville

Today’s Great Salt Lake is a shallow, salty remnant of ancient Lake Bonneville. The Lake occupies the lowest part of the Bonneville basin located in the Great Basin hydrological province. The size, shape, and location of this basin is controlled by tectonics, in particular the faulting and stretching of Earth’s crust that has created a pattern of mountains and valleys that define the Basin and Range physiographic province. Other relics of Lake Bonneville are Utah Lake, Sevier Lake, and the Great Salt Lake Desert which contains the famous Bonneville Salt Flats. Much of the salt now contained in Great Salt Lake was originally in the water of Lake Bonneville. Even though Lake Bonneville was freshwater, it contained salts that concentrated as its water evaporated and the lake contracted. About two million tons of dissolved salts, leached from the soil and rock in the Bonneville basin, is deposited in Great Salt Lake every year by rivers that flow into the lake.

Great Salt Lake water levels have varied by more than 20 feet in historical time, resulting in shoreline shifts of as much as 20 miles.

Great Salt Lake Basics

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 3 million acre-feet of water evaporates from the lake each year.

Great Salt Lake averages approximately 75 miles long by 35 miles wide at a water surface elevation of about 4,200 feet. At this elevation, the lake covers an area of 1,034,000 acres, and has a maximum depth of about 33 feet. Typically, the lake level fluctuates one to two feet annually, rising to its highest level during May through July (following the melting of the mountain snowpack) and dropping to its lowest point during October through November (after the hot summer months).

Image Caption: Great Salt Lake water levels have varied by more than 20 feet in historical time, resulting in shoreline shifts of as much as 20 miles.

PI-39:Commonly Asked Questions About Utah's Great Salt Lake and Ancient Lake Bonneville

Lake Bonneville Basics

Lake Bonneville was a massive, Ice Age lake that existed from about 30,000 to 13,000 years ago. It occupied a low, bowl-shaped depression in the eastern Great Basin. At its largest extent, it spanned about 20,000 square miles of western Utah and parts of eastern Nevada and southern Idaho.

Lake Bonneville was about 325 miles long, 135 miles wide, and had a maximum depth of over 1,000 feet. It contained many islands that are the present-day mountain ranges of western Utah. Its relatively fresh water was derived from direct precipitation, rivers, streams, and meltwater from glaciers. During the time of Lake Bonneville, the climate was somewhat wetter and colder than now.

Lake Bonneville water levels started dropping significantly around 16,000 years ago when the climate began drying and warming, increasing evaporation and decreasing precipitation, which caused a shift in the water balance. In about 2,000 years, the lake had dropped to about the level of modern Great Salt Lake.

Image Caption: Outline of ancient Lake Bonneville and associated modern features (BSF = Bonneville Salt Flats)

TitleTopicYear
Trek to Fremont Island (Disappointment Island) Landforms 2022
Microbialites of Bridger Bay, Antelope Island, Great Salt Lake Microbialites 2022
What Movies Feature Utah Geology? Film and Geology 2022
The Significance of Great Salt Lake’s North Arm on Lake Salinity Great Salt Lake 2021
What were those strange white mounds along the shores of Great Salt Lake? Great Salt Lake 2020
Hole-in-the-Ground, Snake Valley, Millard County, Utah Limestone Geology 2019
The Salt Crust on Great Salt Lake’s North Arm Great Salt Lake 2016
More Than a Grain of Salt: The Salt Crust on Great Salt Lake’s North Arm Minerals 2016
Point of the Mountain, Salt Lake and Utah Counties Landforms 2016
What is the Boxcar Seawall? Great Salt Lake 2015
Microbial Carbonate Reservoirs and the Utah Geological Survey’s “Invasion” of London Microbes 2014
Utah’s potash resources and activity Mining 2012
Bonneville Salt Flats Lake Bonneville 2012
Is there coral in Great Salt Lake? Great Salt Lake 2012
New Classification Scheme – Great Salt Lake Wetlands Great Salt Lake 2011
How many islands are in Great Salt Lake? Great Salt Lake 2010
Utah’s Pleistocene Fossils: Keys for Assessing Climate and Environmental Change Ice Age 2010
Utah potash: resources, production, and exploration Mining 2010
Great Salt Lake – The Titanium Connection Mining 2008
G.K. Gilbert Geologic View Park, Salt Lake County Landforms 2008
Great Salt Lake Trivia Questions Great Salt Lake 2007
Rozel Point and Spiral Jetty Revisited, Box Elder County Great Salt Lake 2006
“Bubblin’ Crude” at Rozel Point, Box Elder County Great Salt Lake 2005
Preguntas Comunes Acerca de Gran Lago Salado de Utah ye de Antiguo Lago Boneville (pdf) Great Salt Lake 2005
Pink Water, White Salt Crystals, Black Boulders, and the Return of Spiral Jetty! Great Salt Lake 2003
What causes the foam on Great Salt Lake? Great Salt Lake 2003
What About Great Salt Lake? Great Salt Lake 2003
Blue-Green Algae: It’s Not Just Pond Scum Great Salt Lake 2003
The Stockton Bar, a Geologic Treasure in Tooele County Lake Bonneville 2001
Hydrologic Cycle Specific to Utah Water 1999
Oft Gestellte Fragen Uberden Groben Salzsee (German version of PI-39) Water 1997
Brine properties, mineral extraction industries, and salt load of Great Salt Lake, Utah (pdf) Great Salt Lake 1997
Commonly Asked Questions About Utah’s Great Salt Lake and Ancient Lake Bonneville Great Salt Lake 1996
The Great Salt Lake Information Sheet (pdf) Great Salt Lake 1990
Major levels of Great Salt Lake and Lake Bonneville (pdf) Lake Bonneville 1984
A Lake Divided – A History of the Southern Pacific Railroad Causeway and Its Effect on Great Salt Lake, Utah Great Salt Lake
The geologic story of GK Gilbert Geologic View Park Geologic History
Lake Bonneville: A Brief History (flash-animated) Lake Bonneville
Mammoth tusk discovery adds to our knowledge of life along the shores of Lake Bonneville Ice Age

Great Salt Lake and Lake Bonneville Articles: 39