The largest lake in the western half of the United States is the Great Salt Lake. The surface area of the lake is greatly affected by the amount of rainfall and the amount of water withdrawn from tributary rivers for irrigation, but on average the Great Salt Lake covers about 940 square miles and is about 75 miles long and 50 miles wide.

The Great Salt Lake is very different from almost every other lake in the world. For one thing it is very shallow, with an average depth of less than 15 feet. For another, it is extremely salty. In fact, the Great Salt Lake is actually saltier than the oceans. The saltiness of the water is very evident in the satellite photo at left. As the water level drops in the lake huge salt deposits are left along the shore, as seen by the whitish areas in the photo. About 200,000 short tons of common salt are taken from the lake every year. The lake contains three parts of salt to every part of other minerals. Glauber's salt, a chemical used in medicines and in industry, is also taken from the lake.

The Great Salt Lake is believed by geologists to be what remains of a much larger lake that once covered almost all of what is now western Utah. Lake Bonneville (as geologists call it) was a great fresh-water lake up to 1,000 feet deep. Water poured into it down the slopes of surrounding mountains. Overflow water found its way to the sea through a gap in the mountains. (Taking a look at the geological map of western Utah at right, it is fairly easy to see just how big Lake Bonneville could have been.)

Over time, however, the climate of the region became much drier. Less water ran into the lake, and much that did evaporated. Eventually the lake lost more water in a year than it received. The lake became shallower and smaller until it finally lost its outlet to the sea. The lake grew salty because the evaporating water left behind the salt it had gathered up from rocks on its way to the lake. As the map shows, several small streams run into the lake today, but none flow out. Every one of those streams run through very salty, mineral-rich sands on their way to the lake, keeping the lake's overall salt concentration fairly constant.

The shores of the several islands in the lake are white with salt. These islands are breeding grounds for large flocks of gulls, ducks, geese, and pelicans. The largest is Antelope Island (shown in the picture at left), where farmers grow alfalfa and raise cattle. There is also a herd of wild buffalo on Antelope Island. There are no fish in the Great Salt Lake, but the waters are full of a species of brine shrimp that is found nowhere else on earth.

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American History.--United States: Local History and Description.--New Southwest. Colorado River, Canyon, and Valley.--Utah.--Regions, Counties, Etc., A-Z.

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