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.

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.

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.

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.

Great Salt Lake averages approximately 75 miles long by 35 miles wide at a 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.

It is reported to be the 33rd largest lake in the world, and the largest fresh or saltwater lake in the United States after the Great Lakes.  Its size and depth, however, vary both seasonally and over the long term.  The magnitude of these changes depends on the balance between the total amount of water that enters the lake and that which leaves.

On average, 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).

In historical time (1847 to present), fluctuations of the lake level have varied over a range of 20 feet from a low of 4,191.35 feet in 1963 to a high of 4,211.85 feet in 1986-1987.  The historical average elevation of the lake is about 4,200 feet.

Because of the very shallow nature of the lake, even modest changes in its elevation result in relatively large changes in the lake’s area and volume.  The accompanying map shows the high, average, and low elevations of the lake and pertinent information for each of these elevations.

The lake contains 11 recognized islands, although this number varies depending on the level of the lake.  Seven islands are in the southern portion of the lake and four in the northwestern portion.

The large islands in the southern portion are named Antelope, Stansbury, Fremont, and Carrington.  The smaller islands are named Badger, Hat (Bird), and Egg.  The four small islands in the northwestern portion are Dolphin, Gunnison, Cub, and Strongs Knob.

Antelope Island has been inhabited since pioneer times.  A ranch house on Antelope Island is said to be the state’s oldest Anglo-built structure on its original foundation and the longest continually inhabited building in Utah. Presently, the Utah Division of Parks and Recreation retains ownership of the ranch house which is open periodically during the summer for tours.

Fremont Island has also been inhabited, most notably by Judge Wenner, a probate judge for Salt Lake County, and his family, from 1884 to 1891.

Both Gunnison and Carrington Islands were unsuccessfully homesteaded for short periods of time.

Antelope Island has been owned by the State of Utah since 1980.  It is home to a large herd of buffalo which is managed by the Utah Division of Parks and Recreation.  Antelope, deer, and many other animals also live on the island.

The northern 2,000 acres of the 23,175-acre island are designated as Antelope Island State Park.  The Antelope Island/Syracuse causeway is the only public-access road connecting the island to the mainland.

Great Salt Lake is divided into two parts by the Southern Pacific Transportation Co. (SPTC) causeway. That part north of the causeway and west of Promontory Mountains is called the north arm, and that to the south of the causeway is called the south arm.

Bear River Bay, although north of the railroad, is considered part of the south arm of the lake. The south arm and Bear River Bay are connected by an opening in the railroad causeway about four miles east of Promontory Point.

In about 1903, the railroad was constructed across the lake as a wooden-trestle structure. The open structure of the trestle allowed for the mixing of water between the north and south arms of the lake. It was built to lessen the distance, degrees of curvature, and time required for trains to travel the previous route around the north end of the lake. By the early 1950s, maintenance costs had become high, and the structure had become unstable under normal operating speeds. Construction of a stable, permanent structure across the lake was needed.

By 1953, the SPTC had decided to replace the wooden trestle with a rock-fill causeway to be built parallel to, and about 1,500 feet to the north of, the old trestle. The structure was completed in 1959 at a cost of roughly $50 million (in 1960 dollars). In 1993, the Trestlewood Division of Cannon Structures, Inc. began to dismantle and salvage the timbers and planking of the old wooden trestle. Salvage operations are still active as of 1995.

The rock-fill causeway has had two major effects on the Great Salt Lake, both related to restricted circulation of water between the north and south arms: (1) the south arm has maintained a higher water level than the north, and (2), the north arm has become saltier than the south.

These conditions persist despite two 15-foot-wide by 20-foot-deep open culverts that were built into the causeway to facilitate water and boat movement between the two arms, and despite a 300-foot-wide breach (opening) which was cut through the causeway near Lakeside in 1984 as a flood-control measure.

The level of the south arm is higher than the north arm because river water enters the south arm at a faster rate than lake water can move northward through the causeway and its openings.

Since the construction of the solid-fill causeway, the salt content (salinity) of the north arm has become greater than the south arm. This is due to the following: (1) the south arm receives nearly all of the freshwater tributary inflow to the lake, and (2) the north arm is fed mainly by south arm salty water seeping through the causeway and flowing through the culverts and the breach opening.

Currently, the north arm of the lake is near its salt-saturation point (24-26 percent) and is about twice as salty as the south arm (12-14 percent).

In 1983, the level of Great Salt Lake began to rise, due to above-average annual precipitation. By 1986, the lake rose nearly 12 feet to reach its historic high of 4,211.85 feet. The high lake level caused serious flooding which resulted in millions of dollars in property damage, especially around the south arm of the lake.

Flooding disrupted major highway and railroad traffic; inundated mineral-industry solar ponds, roads, beaches, farms, boating facilities and state/federal waterfowl management areas; and threatened water-treatment plants.

In 1984, after studying numerous flood-control alternatives, the State of Utah implemented its first flood-control project by breaching the SPTC causeway. The breach consisted of a 300-foot-long bridge-covered opening in the causeway near Lakeside, which allowed the rapid flow of south-arm water into the north arm.

Breach in the SPTC causeway, near Lakeside, looking northeast. Photo by P.A. Sturm.

Close-up view of first waters flowing through the breach opening.

Prior to the breach, the elevation of the south arm was over 3.5 feet higher than the north arm. Completed at a cost of about 3.5 million dollars, the project lowered the south arm of the lake by nearly one foot and raised the north arm by about 1.5 feet, within about two months.

The lake continued to rise after the causeway breach was completed, forcing the State to implement its second flood-control alternative, pumping water from the lake into the West Desert.

Three large pumps installed on the western shore of the lake pumped water via a 4.1-mile-long canal to the West Pond. The pumping project filled the 320,000-acre West Pond with over 800,000 acre-feet of water and greatly increased the net evaporation from the lake. The West Desert Pumping Project was completed at a cost of more than $60 million.

West Desert pumping plant. Water was pumped from the north arm of the lake through a 4.1-mile-long canal to the 320,000-acre West Pond.

Close-up view of the pumping plant with one of the three 1,000 cubic-feet-per-second pumps in operation (view looking east).

For more than two years, starting in 1987, water was pumped from the north arm of the lake into the West Pond evaporation area in the west desert. During the 26-month life of the project, more than 2.7 million acre-feet of water were pumped, which contained about 695 million tons of salt.

The pumps are currently not in use but are maintained in ready condition should the lake rise again.

The total amount of salt dissolved in Great Salt Lake is about 4.5 to 4.9 billion tons.  As the lake rises, its salinity drops because the same amount of salt is dissolved in more water.  The lower the lake level, the saltier the lake becomes.  In historical time, the lake’s salinity has ranged from a little less than 5 percent, (just above that of sea water), to nearly 27 percent (beyond which water cannot hold more salt).

You can easily float in Great Salt Lake if the water is salty enough.  At the lake’s average elevation of 4,200 feet, the south arm of the lake contains about 13 percent salt, which makes it salty enough for most people to float with little effort.  When the lake is higher than 4,200 feet, it is less salty and therefore less buoyant.  Swimmers float easily in the north arm because it is twice as salty as the south arm.

The chemical composition of Great Salt Lake is similar to that of typical ocean water.  Sodium and chloride are the major ions in the water, followed by sulfate, magnesium, calcium, and potassium.  For comparison, the table below shows the concentration of the six major ions in water of Great Salt Lake, a typical ocean, and the Dead Sea.

Chemical compositions (dry weight percents) of Great Salt Lake, typical ocean, and the Dead Sea waters.
Source	Sodium	Potassium	Magnesium	Calcium	Chloride	Sulfate
Great Salt Lake	32.8	2.0	3.3	0.2	54.5	7.2
Ocean (typical)	30.8	1.1	3.7	1.2	55.5	7.7
Dead Sea	12.3	2.3	12.8	5.3	67.2	0.1

The Great Salt Lake and its environs have been used by swimmers, boaters, bikers, hikers, and hunters for recreational purposes from the mid-1800s to the present.

Long-term water-level fluctuations, both high and low, have adversely affected lake recreation over the years, however.  Nearly a dozen resorts have either been flooded or left high and dry.

The most famous resort, Saltair, was built in 1893 and destroyed by fire in 1971.  The lake and and its three state parks, Great Salt Lake Saltair Beach, Antelope Island, and Willard Bay, attracted over a million tourists in 1994.

The extraction of common salt from the lake started in the mid-1800s and continues to be an important part of the State’s economy.  Other products, including magnesium metal, chlorine gas, sodium and potassium sulfate, and magnesium chloride, have been extracted since the early 1960s.

Oil occurs in natural seeps on the north shore of the lake, and drilling in the late 1970s disclosed additional oil beneath the bed of the lake.  The brine-shrimp industry harvests brine-shrimp eggs, for use as fish food, and exports them world wide.

Eight state waterfowl management areas and one federal migratory bird refuge dot the southern, northern, and eastern shores of the lake.  Established during the early 1900s, these areas serve as important resting, feeding, and nesting areas for millions of ducks, geese, grebes, shorebirds, and other water-dependent birds.  Visitors are always welcome, and hunting is generally allowed during the regular waterfowl hunting season.

In 1995, five mineral-extraction companies operated near the lake. These companies used solar evaporation to concentrate the lake waters to produce either salts or highly concentrated brine (water with high salt content) products. These companies paid a royalty to the State of Utah (owner of the lake), on the salts and other materials produced and sold.

Sodium chloride (common salt) is produced by: (1) evaporating the water in shallow ponds that cover many thousands of acres, (2) precipitating the salt, and (3) harvesting it from the bottom of the ponds.The collected salt is rinsed, washed, dried, and screened to produce different product sizes and grades.

Common salt is also pressed into pellets for use in water softeners, and formed into salt-lick blocks (some with added minerals) for livestock consumption. Large quantities of bulk salt are shipped out-of-state for use in industry. Much of the salt is used locally for melting ice on roadways.

Food-grade, or table salt is not produced from the lake, because its purity cannot be guaranteed without additional, costly processing. The table salt used in Utah comes from salt-processing facilities in New York, Ohio, Kansas, Louisiana, Texas, or California.

Great Salt Lake also yields salt products other than common salt. The salt industry produces potassium sulfate, a commercial fertilizer derived from potassium and magnesium salts.

Magnesium-chloride brine is used in the production of magnesium metal and chlorine gas and as a dust suppressant. The production of these salts and highly concentrated brines requires additional evaporation beyond that needed to precipitate common salt. These products also require complex chemical processing.

Mirabilite, a hydrated sodium-sulfate salt, commonly used in the production of sodium sulfate or salt cake, precipitates from concentrated lake water only during the cold winter months.

The table below lists the names of the five salt companies that operated on the Great Salt Lake and the products they produced.

Companies extracting mineral products from the Great Salt Lake, and their products (1995).
COMPANY	PRODUCTS
AKZO Salt of Utah	Sodium chloride
Great Salt Lake Minerals Corp.	Potassium sulfate and magnesium chloride products
Magnesium Corporation of America	Magnesium metal, chlorine gas
Morton Salt Company	Sodium chloride
North American Salt Company	Sodium chloride

The tiny brine shrimp (Artemia salina) is one of the few  animals that lives within Great Salt Lake. The brine-shrimp population plays an important part in the lake’s ecosystem, especially in keeping the lake waters clean through algae consumption. They are also a major food source for millions of migrating birds.

Other forms of life associated with the lake include brine flies, algae, and bacteria. Brine flies congregate by the millions along the lake’s beaches, where they feed on bacteria and algae that grow on rocks or wood. The wind commonly blows the remains of dead brine flies into long, black, odoriferous windrows or piles along the beaches. Numerous species of algae and bacteria, which cause the varied colors of the lake waters, provide food for the brine shrimp.

Ducks, geese, gulls, pelicans, and hundreds of other types of birds live in the marshes and wetlands surrounding the lake. Great Salt Lake is an important part of the Pacific and Central Flyways for migratory waterfowl and part of the Northern Hemispheric Shorebird Reserve Network.

The shores and nearby wetlands of the lake are also home to a variety of reptiles and mammals. Eight amphibian, two turtle, nine lizard, and eight snake species, as well as total of 64 species or subspecies of mammals have been identified in the Great Salt Lake area.

Due to its large size, Great Salt Lake has a significant affect on the weather of nearby cities. During the winter, the lake is warmer than the air above it. This increases the moisture content of the air, creates thermal instability, and causes natural seeding of salt crystals. These factors are believed to cause the fall and winter “lake effect,” in which areas adjacent to and usually downwind from the lake receive greater snowfall than those more distant.

The unpleasant odor (resembling rotten eggs) that comes from the lake is a common complaint from those who live near the lake. The odor results from the decay of plant and animal remains in the shallow waters around its shores, especially in Farmington Bay. This odor is especially noticeable when northwest winds blow across the lake, stir up the shallow waters, and carry the odor landward to populated regions.

The quantities of harmful contaminants in the lake, such as industrial organic wastes, copper, arsenic, mercury, cadmium, and lead are very low. This is contrary to what one might expect since rivers, waste-water treatment plants, and industrial facilities discharge into the lake.

The lake ecosystem appears to cleanse itself of certain types of contaminants through chemical and biological processes. More study is needed to understand these cleansing processes, however.

The Bonneville Salt Flats are located west of Great Salt Lake near the town of Wendover on the Utah-Nevada border, about 115 miles west of Salt Lake City. The flats are a broad, salt-covered lake bed, and one of the flattest areas on earth. They were formed during the final evaporative stages of Lake Bonneville.

The salt flats are the site of high-speed car-racing events. In 1970, Gary Gabolich of the U.S. piloted the Blue Flame (rocket-powered) racer to a speed of 622.407 miles per hour, a Bonneville Salt Flats speed record which still stands as of 1995.

In the past 30 years, there has been an apparent deterioration of the racing surface. This has become a controversial issue involving the U.S. Bureau of Land Management, those who race on the salt flats, and a company that produces potassium chloride salt and magnesium chloride (brine) from salt-flat brine. Studies are underway to determine why the salt is disappearing, if the loss can be stopped, and if the salt can be replaced.

The 1,200-foot-tall smoke stack at the southern end of the lake is part of the Kennecott Copper Company’s copper ore-smelting operation. Ore for this smelter comes from the Bingham Canyon copper mine, which is the largest open-pit excavation on earth. The Bingham Canyon mine, started in 1906, is located approximately 15 miles to the south of the lake on the eastern side of the Oquirrh Mountains.

The round, brown-to-white grains that make up many of the beaches around the lake are called oolites. Oolites are small spherical to elongated grains composed of concentric layers of calcium carbonate built up around a central core, much like a pearl. The core material is usually a small mineral grain, or a brine shrimp fecal pellet.

Some of the most beautiful beaches around the lake are composed of oolitic sand.

Magnified view of typical oolites

Oolite cross section showing concentric layers built up around a central mineral fragment.

FOR GEOLOGICAL, WATER SALINITY/CHEMISTRY, AND GENERAL LAKE INFORMATION: Utah Geological Survey, 1594 W. North Temple, Suite 3410, Salt Lake City, UT, 84114-6100, (801) 537-3326 or (801) 537-3366.

FOR LAKE ELEVATIONS AND HYDROLOGY INFORMATION: U.S. Geological Survey, 2329 West Orton Circle, West Valley City, UT 84119, (801) 908-5000.

FOR RECREATION, BOATING, LAKE-ACCESS, AND SEARCH-AND-RESCUE INFORMATION: Division of Parks and Recreation, 1594 W. North Temple, Suite 116, Salt Lake City, UT 84114-6001, (801) 538-7220.

FOR LEASING AND MINERAL EXTRACTION/ROYALTY INFORMATION IN THE GREAT SALT LAKE: Utah Division of Forestry, Fire and State Lands, 1594 W. North Temple, Suite 3520, Salt Lake City, UT 84114-5703, (801) 538-5555.

FOR WATER RESOURCES AND LAKE-LEVEL CONTROL PROGRAM INFORMATION: Utah Division of Water Resources, 1594 W. North Temple, Suite 310, Salt Lake City, UT 84114-6201, (801) 538-7230.

FOR WATER APPROPRIATIONS, DISTRIBUTIONS, AND ADJUDICATIONS: Utah Division of Water Rights, 1594 W. North Temple, Suite 220, Salt Lake City, UT 84114-6300, (801) 538-7240.

FOR WILDLIFE AND BRINE SHRIMP INFORMATION: Utah Division of Wildlife Resources, 1594 W. North Temple, Suite 2110, Salt Lake City, UT 84114-6301, (801) 538-4700.

FOR CONSTRUCTION IN AND AROUND THE LAKE (401 PERMIT) INFORMATION: U.S. Army Corps of Engineers, 1403 S. 600 W., Woods Cross, UT 84087, (801) 295-8380.

FOR BONNEVILLE SALT FLATS AND FEDERAL LAND-LEASING INFORMATION: U.S. Bureau of Land Management, Salt Lake City District Office, 2370 S. 2300 W., Salt Lake City, UT 84119, (801) 977-4300.

FOR BEAR RIVER MIGRATORY BIRD REFUGE INFORMATION: U.S. Fish and Wildlife, Bear River Migratory Bird Refuge, 866 S. Main, Brigham City, UT 84302, (801) 723-5887.

• Major Levels of Great Salt Lake and Lake Bonneville by D.R. Curry, G. Atwood, D. Mabey, 1983.
• Great Salt Lake; a Scientific, Historical and Economic Overview, editor: J.W. Gwynn, 1980.
• The Great Salt Lake, Utah, by W.L. Stokes, 1984.
• Geologic Resources of Box Elder County, Utah by S.N. Eldredge, M.H. Bugden, and C.M. Wilkerson, 1989.
• Great Salt Lake Information Sheet, 1990.
• Geology and Antelope Island State Park, Utah by H.H. Doelling and others, 1988.
• Geologic Resources of Box Elder County, Utah by S.N. Eldredge, M.H. Bugden, and C.M. Wilkerson, 1989.
• Antelope Island State Park, Davis County, Utah, 1995.
• Geologic Map of Antelope Island, Davis County, Utah by H.H. Doelling and others, 1991.
• Engineering Geology of the Salt Lake City Metropolitan Area, Utah by W.R. Lund, 1990.
• Dissolved-Mineral Inflow to Great Salt Lake and Chemical Characteristics of the Salt Lake Brine, Part I, 1963 by D.C. Hahl and C.G. Mitchell; and Part II, 1964 by D.C. Hahl and R.H. Langford, 1964.
• Great Salt Lake, Utah: Chemical and Physical Variations of the Brine, 1963-1966by D.C. Hahl and A.H. Handy, 1969; 1966-1972 by J.A. Whelan, 1973; 1973 by J.A. Whelan and C.A. Peterson, 1975; 1974-1975 by J.A. Whelan and C.A. Peterson, 1977.
• Effects of a Causeway on the Chemistry of the Brine in Great Salt Lake, Utah by R.J. Madison, 1970.
• Evaluation of Eddy Flux Techniques in Computing Evaporation from the Great Salt Lake, by D.R. Dickson and A.E. Rickers, 1970.
• The Effects of Restricted Circulation on the Salt Balance of Great Salt Lake, Utahby K.M. Waddell and E.L. Bolke, 1973.
• Hydrogeology of the Bonneville Salt Flats, Utah by L.J. Turk, 1973.
• Model for Evaluating the Effects of Dikes on the Water and Salt Balance of Great Salt Lake, Utah by K.M. Waddell and F.K. Fields, 1977.
• Effects of Breaching the Southern Pacific Railroad Causeway, Great Salt Lake, Utah – Physical and Chemical Changes, August 1, 1984 – July, 1986 by J.W. Gwynn and P.A. Sturm, 1987.
• Geology and Mineral Resources of Box Elder County, Utah by H.H. Doelling, 1980.
• Shallow Ground Water and Related Hazards in Utah by S. Hecker and K.M. Harty, 1988.
• Flood Hazards from Lakes and Failures of Dams in Utah by K.M. Harty and G.E. Christenson, 1988.
• Glauber’s Salt Bed West of Promontory Point, Great Salt Lake by A.J. Eardley, 1962.
• Gypsum Dunes and Evaporite History of the Great Salt Lake Desert by A.J. Eardley, 1962.
• Clay Mineralogy at the Brine-Sediment Interface in the South Arm of Great Salt Lake, Utah by L.L. Hedberg and W.T. Parry, 1971.
• Preliminary Report on Possible Solutions to”Fill Effect” causing Dilution of South Arm Brines and Concentration of North Arm Brines, Great Salt Lake, Utah by J.A. Whelan and N. Stauffer, 1972.
• Mineral Occurrences in the Emergency Withdrawal Area and Adjacent Lands in the Great Salt Lake Desert by J.W. Gwynn and others, 1985.
• An Approximation of the Physical and Chemical Characteristics of Farmington Bay and Bear River Bay, Great Salt Lake, Utah by J.W. Gwynn, 1986.

I thank the following individuals for submitting commonly asked questions or reviewing this document: Bryce Tripp, Rebecca Hylland, Carol Oestreich, David Madsen, Bill Case, Bill Jerome, Richmond Kelley, Rebecca McNeeley, Corey Milne, Carolyn Olson, Sharon Wakefield, Jim Fillpot, Scott Flandro, Teddie Krause, Kimm Harty, and Tom Aldrich.

Special thanks is given to Dr. Don Currey, University of Utah, for providing current information on the elevations and ages of Lake Bonneville and Great Salt Lake shorelines.