| In the Desert Southwest, 'playa' also refers to one of the many vast lakebeds that fill the valleys. These were formed during a wetter time, during the ice ages. As the climate dried, the lakes gradually disappeared, leaving only a flat layer of white saline ground. Many of these lakebeds will fill with a very shallow layer of water after storms. Sometimes the layer will be so thin that it moves from one side of the playa to the other depending on the wind. Other times they can be several feet deep and many miles across.
Because these playas were once much larger lakes, often they are surrounded by old 'beaches' and terraces which are often hundreds of feet above the surface of the valley and encircle the playas like bathtub rings.
Playas are abundant in the Mojave Desert, and i'm sure in other deserts of the world, albeit under different names. One of the largest playas around is the Bonneville Salt Flats, which is used for racing extremely fast cars because it is perfectly flat. Some playas are mined for borax, salt, or other minerals. In the Death Valley area, there is a playa called 'the racetrack' where rocks mysteriously move around the surface, leaving long tracks in the mud. Another playa in the area has crystalized into bizarre formations and is now called the devil's golf course. A playa formed in the place of Owens Lake in recorded history as Los Angeles dried up the Owens River. Mono Lake barely avoided the same fate. | 
