A Look at the Playa

Understanding dry lake beds

Salar de Uyuni, Bolivia
At over 4,000 square miles, Bolivia's Salar de Uyuni is the largest playa in the world. Westend61/Getty Images

Everywhere that you can find deserts, you can find dry lake beds. Known as playas (plahy-uh) in the western United States, these former lakes are dry and harsh places, avoided by most animals and vegetation. But they're the best setting in the world for certain activities: Launching rockets. Landing the Space Shuttle. Breaking land speed records. Staging grueling ultramarathons. And every year in Nevada's Black Rock Desert, celebrating the Burning Man arts festival.

What geologic processes create these remarkable, flat expanses of land?

To Make a Dry Lake Bed

To start, you need a desert. In the most arid places, permanent rivers are rare, and they are slow to construct the kind of depositional stream networks that we see in temperate regions. Where mountains are actively growing, as in the American West, the basins between ranges tend to be bowls with closed drainage systems. These closed drainage systems that retain water and have no outlet are known as endorheic basins. Where the landscape is old and flat, as in Arabia and southern Africa, the movements of sand dunes create many endorheic basins. These basins, however they are formed, hold shallow lakes during parts of the year.

Only the finest sediment reaches the center of a desert basin: particles of silt and clay size. Both wind and water carry this material. Water also brings with it dissolved minerals, and as the desert lakes dry up these minerals come out of solution.

Among these are calcite and gypsum, which tend to cement the lake bed mud and turn it into a hard, smooth surface. 

Other minerals are salts, mostly halite—the same substance as table salt. Where halite is abundant, dry lake beds turn into salt flats. The world's largest salt flat is the Salar de Uyuni in Bolivia, where a thick layer of salt supports a local mining industry.

Out in its center, the landscape resembles a salt Antarctica. And in America there's the Bonneville Salt Flats in Utah, a place so flat that you can see the Earth's curvature as you look across it.

Not every dry lake bed is a salt flat. Many are paved with silt and clay, like Rogers Dry Lake Bed in southern California. Its surface is so perfect that aircraft runways can be created by simply painting an outline on the ground. The U.S. Air Force tests experimental aircraft there, and the Space Shuttle lands there when conditions are poor in Florida. It's also a well-known site for emergency crash landings, whenever an airplane with broken landing gear needs to come down safely.

Why a Playa?

Dry lake beds have many different names around the world: they are salars in Latin America, sabkhas in north Africa, vloers in south Africa, faydah in Arabia, takirs or bahirs in central Asia and kavirs in Iran. But in the deserts of the United States the most common term is playa, the same word Spanish speakers use to refer to the beach.

The seashore would seem like the opposite of a totally flat expanse of dry dust. But maybe a playa is a kind of beach without an ocean. Perhaps this usage of "playa" is just wry frontier humor; that wouldn't be out of character.

PS: There are plenty of other people having serious fun on the playa. Consider the Rocketry Organization of California, which launches huge amateur rockets from the flats of Lucerne Dry Lake every second Saturday of the month. Spectators are welcome at no charge.

Edited by Brooks Mitchell