The Great Salt Lake and Ancient Lake Bonneville

The Great Salt Lake in Utah is a Remnant of the Ancient Lake Bonneville

The Bonneville Salt Flats is the remnant of Lake Bonneville which covered one third of the State of Utah over 10,000 years ago. It is one of the most consistently flat areas on earth, which makes it the ideal home for landspeed record attempts. Dan Callister/Getty Images

The Great Salt Lake is a very large lake located in northern Utah in the United States. It is a remnant of the even larger prehistoric Lake Bonneville and today is the largest lake west of the Mississippi River. The Great Salt Lake is about 75 miles (121 km) long and 35 miles (56 km) wide and it is located between the Bonneville Salt Flats and Salt Lake City and its suburbs. The Great Salt Lake is unique because of its very high salt content. Despite this, it provides habitat for many birds, brine shrimp, waterfowl and even antelope and bison on its Antelope Island. The lake also provides economic and recreational opportunities for the people of Salt Lake City and its surrounding communities.

Geology and Formation of the Great Salt Lake

The Great Salt Lake is a remnant of the ancient Lake Bonneville that existed during the last ice age which occurred from around 28,000 to 7,000 years ago. At its largest extent, Lake Bonneville was about 325 miles (523 km) wide and 135 miles (217 km) long and its deepest point was over 1,000 feet (304 m). It was created because at that time the climate of the present-day United States (and the entire world) was much cooler and wetter. Many glacial lakes were formed around the western United States at this time because of the different climate but Lake Bonneville was the largest.

At the end of the last ice age, about 12,500 years ago, the climate around present-day Utah, Nevada and Idaho began to warm and become drier. As a result, Lake Bonneville started shrinking as it is located in a basin and evaporation exceeded precipitation. As it shrank the level of Lake Bonneville fluctuated greatly and previous lake levels can still be seen on the terraces that were eroded into the land surrounding the lake (PDF map of Lake Bonneville’s various shorelines). Today’s Great Salt Lake is what is left of Lake Bonneville and it fills in the deepest portions of that lake’s great basin.

Like Lake Bonneville, the Great Salt Lake’s water level often fluctuates with differing amounts of precipitation. There are 17 islands that are officially recognized but because they are not always visible, many researchers say there are 0-15 islands (Utah Geological Survey). When lake levels are down, other many small islands and geologic features can show up. In addition, some of the larger islands, such as Antelope, can form land bridges and connect to neighboring areas. The largest of the 17 official islands are Antelope, Stansbury, Fremont and Carrington islands.

In addition to its large size and many land forms, the Great Salt Lake is unique because of its very salty water. The water in the lake is salty because Lake Bonneville formed out of a small saline lake and although it became fresher after growing to its maximum size the water still contained dissolved salts and other minerals. As the water in Lake Bonneville began to evaporate and the lake shrank, the water again became saltier. In addition, salt still leaches out of rocks and soils from surrounding areas and is deposited in the lake by rivers (Utah Geological Survey). According to the Utah Geological Survey, about two million tons of dissolved salts flow into the lake every year. Because the lake does not have a natural outlet these salts stay, giving Great Salt Lake its high salinity levels.

Geography, Climate and Ecology of the Great Salt Lake

The Great Salt Lake is 75 miles (121 km) long and 35 miles (56 km) wide. It is located near Salt Lake City and is within the counties of Box Elder, Davis, Tooele and Salt Lake. The Bonneville Salt Flats are west of the lake while the land surrounding the northern part of the lake is mostly undeveloped. The Oquirrh and Stansbury mountains are south of the Great Salt Lake. The depth of the lake varies throughout its area but it is deepest in the west between the Stansbury and Lakeside mountains. It is important to note that with varying precipitation levels the depth of the lake also varies and because it is located in a very wide, flat basin, a slight rise or decrease in water level can drastically change the total area of the lake (

Most of the Great Salt Lake’s salinity comes from the rivers that feed into it as salt and other minerals are leached from the areas through which they flow. There are three major rivers flowing into the lake as well as several streams. The main rivers are the Bear, Weber and Jordan. The Bear River starts out in the Uinta Mountains and flows into the lake in the north. The Weber River also starts in the Uinta Mountains but flows into the lake along its eastern shore. The Jordan River flows out of Utah Lake, which is fed by the Provo River, and meets the Great Salt Lake in its southeast corner.

The Great Salt Lake’s size and relatively warm water temperature is also important to the climate of the region surrounding it. Because of its warm waters it is common for places like Salt Lake City to receive large amounts of lake effect snow during the winter. In the summer, large temperature differences between the lake and surrounding land can cause thunderstorms to develop over the lake and in the nearby Wasatch Mountains. Some estimates claim that about 10% of Salt Lake City’s precipitation is caused by the effects of the Great Salt Lake (

Although the high salinity level of the Great Salt Lake’s waters do not support much fish life, the lake has a diverse ecosystem and is home to brine shrimp, an estimated one hundred billion brine flies and many types of algae ( The lake’s shores and islands provide habitat for a wide range of migrating birds (who feed on the flies) and islands such as Antelope have populations of bison, antelope, coyote and small rodents and reptiles.

Human History of the Great Salt Lake

Archeological records show that Native Americans lived near the Great Salt Lake for many hundreds of years but European explorers did not learn of its existence until the late 1700’s. Around that time Silvestre Velez de Escalante learned of the lake from Native Americans and he included it in is records as Laguna Timpanogos, although he never actually saw the lake (Utah Geological Survey). Fur trappers Jim Bridger and Etienne Provost were later the first to see and describe the lake in 1824.

In 1843, John C. Fremont, led a scientific expedition to survey the lake but it was not completed due to harsh winter conditions. In 1850 Howard Stansbury finished the survey and discovered the Stansbury mountain range and island, which he named after himself. In 1895, Alfred Lambourne, an artist and writer, spent a year living on Gunnison Island and he wrote a detailed account of his life there called Our Inland Sea.

In addition to Lambourne, other settlers also began to live and work on the Great Salt Lake’s various islands throughout the mid to late 1800’s. In 1848 the Fielding Garr Ranch was established on Antelope Island by Fielding Garr who was sent by the Church of Jesus Christ of Latter-day Saints to ranch and manage the church’s herds of cattle and sheep. The first building he constructed was an adobe house that still stands and is the oldest building in Utah. The LDS Church owned the ranch until 1870 when John Dooly, Sr. purchased it to improve the ranching operations. In 1893 Dooley imported 12 American Bison in an attempt to ranch them as their wild populations declined. Ranching operations at the Fielding Garr Ranch continued until it became a protected part of the Antelope Island State Park in 1981.

Activities on the Great Salt Lake Today

Today Antelope Island State Park is one of the most popular places for visitors to see the Great Salt Lake. It offers large, panoramic views of the lake and surrounding areas as well as many hiking trails, camping opportunities, wildlife viewing and beach access. Sailing, paddle boarding, kayaking and other boating activities are also popular on the lake.

In addition to recreation, the Great Salt Lake is also important to the economy of Utah, Salt Lake City and other surrounding areas. Tourism as well as salt mining and other mineral extraction and the harvest of brine shrimp provide a large amount of capital for the region.

To learn more about the Great Salt Lake and Lake Bonneville, visit the official website for the Utah Geological Survey.