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Why did the Great Basin have many brackish and salty lakes?

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Indigenous peoples of the Great Basin Kaylei Weed (left) of the Eastern Shoshone Tribe with her two sons and mother, Elaine Ethel Weed, at the Wind River Indian Reservation in 2015.

The Great Basin is characterized by an arid to semiarid climate where water does not leave the region through traditional river outlets to the sea. Because the region consists of closed, or endorheic, drainage basins, water can only exit the system through evaporation or seepage.123

As rivers and streams flow into these basins, they carry dissolved mineral salts with them. Because there is no outlet for this water to continue its journey, the water eventually evaporates, leaving the accumulated mineral salts behind in the basin floors. Over time, this process leads to the formation of brackish and salty lakes, such as the Great Salt Lake.413

These lakes are highly sensitive to the balance between water input—from precipitation and runoff—and water output—from evaporation. In the Great Basin, evaporation rates typically exceed the supply of water, which causes the lakes to become increasingly saline. This cycle of internal drainage and high evaporation is the primary reason for the prevalence of saline environments throughout the region.234