The Great Salt Lake is the largest salt lake in the western Hemisphere.

Before the ancient Lake Bonneville evaporated, leaving the Great Salt Lake covering only 1,700 square miles, Bonneville inundated much of present-day Utah and small parts of Nevada and Idaho during the Great Ice Age, between 32,000 and 14,000 years ago.

It is now what’s known as a “terminal” lake, which has no outlet waterways flowing to the ocean. The only way water can leave the lake is through evaporation, causing the remaining water to be salty with dissolved minerals from the lake’s sources and basin.

Although it has been called “America’s Dead Sea,” the lake actually provides a habitat for millions of native birds, brine shrimp, shorebirds and waterfowl.

In the satellite image, a sharp boundary between two shades of green water in the lake can clearly be seen. This is due to a 12-mile long railroad levee constructed in the late 1950s.

Since the dirt structure obstructs almost all of the flow between the upper and lower parts of the lake, salt concentrations have become different in the two sections over the past 50 years. The dark and light green colors reflect the difference.

The solid raised roadway, made of 50 million cubic yards of rock, sand and gravel, is said to be safer and allows trains to travel across it at faster speeds than on the previous wooden trestle.

Image: European Space Agency