The largest lake in the western half of the United States is Great Salt Lake. This lake is very different from the Great Lakes. For one thing, it is very shallow. On the average it is less than 15 feet deep. Besides, its water is very salty.
   This lake is left over from a much bigger one—Lake Bonneville. Lake Bonneville once covered most of what is now the state of Utah. It was a great fresh-water lake 1,000 feet deep. Water poured into it down the slopes of surrounding mountains. Through a gap in the mountains overflow water found a way to the sea.
   But in time the climate of the region became much drier. Less water ran into the lake, and much that did evaporated. Finally the lake was losing more water each year than it got. Of course, the lake became shallower and smaller. At last no water ran out of it to the sea. The lake grew salty, for the water as it evaporated left behind the salt it had gathered up from rocks on its way to the lake. Now the water is much saltier than sea water. The only living things in Great Salt Lake are brine shrimps and tiny algae. Swimming in such salty water is a strange experience. The water holds a swimmer up much more than fresh water does. If he floats, a third of his body is out of water. Diving is rather dangerous. A diver may be stunned when he hits the heavy water.
    Along the northwest shore of the lake are the Bonneville Salt Flats. "Flats" is a good name for them, for they are probably flatter than any other natural surface on the earth. The ground is almost pure salt. On the Flats there is an automobile racecourse. A racing car has traveled nearly 400 miles an hour on it.
   Salt Lake City is near Great Salt Lake. Some of the people of the city earn their living by mining salt. Lake Bonneville left behind enough salt to last the whole world for a thousand years.
   The best way to get a good view of the lake is to fly over it. On a sunshiny day the very blue lake with its border of salt makes a picture it is not easy to forget.