Visual Glossary

The white, mirage-like surface of Soda Dry Lake, a playa in Mojave National Preserve. Photo by Bonnie Murchey, USGS.

Playas

Playa lakes are among the flattest landforms in the world. They form under arid conditions when water drains into basins with no outlet to the sea and quickly evaporates. In wet years, the playas may fill with standing water. Under the hot desert sun the thin veneer of water quickly evaporates, leaving a level surface of silt, clay, and mineral salts behind.

Racetrack Playa, Death Valley National Park. Photo by Marli Miller

At Soda Dry Lake in Mojave National Preserve water may lie very near the surface of the playa even during the hottest, driest times of the year. Capillary action draws the water upward where it evaporates, leaving a white, puffy crust of evaporite minerals such as sodium carbonate and sodium bicarbonate.

Racetrack Playa in Death Valley National Park is another, almost perfectly flat dry lake bed. During periods of heavy rain, water washes down the nearby mountain slopes into the playa, forming a shallow, short-lived lake. Under the hot Death Valley sun water quickly evaporates, leaving behind a layer of soft mud. As the mud dries, it shrinks and cracks into a mosaic of interlocking polygons.