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A dry lake is an ephemeral lakebed, or a remnant of an endorheic lake. Such flats consist of fine-grained sediments infused with alkali salts. Alternative names for the dry lake include alkali flat, alkali sink and playa.
A playa lake may cover a wide area, but it is never deep. Most water in it evaporates, leaving a layer of salt on the surface. These salt covered stretches are called saltpans.
The Spanish word playa (pronounced: [ˈplaʝa]) literally means "beach". Dry lakes are known by this name in some parts of Mexico and the western United States. This term is also used on the Llano Estacado and other parts of the Southern High Plains.
In South America, the usual term for a dry lake is salar or salina, Spanish for "salt pan".
Pan is the term used in most of South Africa. These may include the small round highveld pans, typical of the Chrissiesmeer area, to the extensive pans of the Northern Cape province, which are sometimes employed for land speed record attempts. It is also used in Australia. Distinguished are salt pans and clay pans.
Hardpan is a dry terminus of an internally drained basin in a dry climate, typically used in the Great Basin of the western US.
In Central Asia, a similar "cracked mud" salt flat is known as a takyr.
In Iran salt flats are called kavir.
The surface of a dry lake is typically dry, hard and rough during the dry season, but wet and very soft in the rainy season. Dry lakes are generally small, round depressions in the surface of the landscape.
A playa lake is formed when rain fills a round depression in the landscape, creating a small lake. The water is generally freshwater, When all of the water evaporates, a playa is formed. The playa appears as a flat bed of clay, generally encrusted with precipitated salts. These evaporite minerals are a concentration of weathering products that have been left behind. Some examples of evaporite minerals are sodium carbonate, borax, and other salts. Playas are often found in bajadas, a depositional landform of desert environments.
Dry lakes can also form when the water table intersects the surface and water seeps into them.
Dry lakes are typically formed in semi-arid to arid regions of the world. The largest concentration of dry lakes in the world (nearly 22,000) is in the southern High Plains of Texas and eastern New Mexico.
The Racetrack Playa, located in Death Valley, California, features "sailing stones" that leave linear "racetrack" imprints. The sailing stones are a geological phenomenon found in the playa. The stones slowly move across the surface, leaving a track as they go, without human or animal intervention. They have never been seen or filmed in motion. The stones only move once every two or three years and most tracks last for three or four years.
Many dry lakes contain shallow water during the rainy season, especially during wet years. If the layer of water is thin and is moved around the dry lake by wind, an exceedingly hard and smooth surface may develop. Thicker layers of water may result in a "cracked-mud" surface and "teepee" structure desiccation features. Very little water can result in dune formation.
While the dry lake itself will typically be devoid of vegetation, they are commonly ringed by shadscale, saltbrush and other salt-tolerant plants that provide critical winter fodder for livestock and other herbivores.
In southwest Idaho and parts of Nevada and Utah are a number of rare species that occur nowhere else but the inhospitable environment of seasonally flooded playas. A new species of giant fairy shrimp was found in 2006- and though a large predatory species- it evaded detection because of the playa's murkiness when filled because of winds and fine clay. It is also a species able to regenerate using tiny undetectable cysts that can remain in a dry lake bed for years until conditions are optimum for the species to hatch.
Lepidium davisii is another rare species- a perennial plant- whose habitat is restricted to playas in southern Idaho and northern Nevada.
Oftentimes in the desert this is the only available water to wildlife away from major rivers or lakes, antelope and other wildlife take advantage of close by playas for drinking water after rainstorms.
Threats to dry lakes include pollution from concentrated animal feeding operations such as cattle feedlots and dairies, erosion, fertilizer, pesticide and sediment runoff from farms, and overgrazing. A non-native shrub that has been used for rangeland restoration in the west- Kochia prostrata- also poses a significant threat to playas and their associated rare species, capable of crowding out natives and draining a playa's standing water because of root growth and the Kochia plants' use of it when available.
The extremely flat, smooth and hard surfaces of dry lakes make them ideal for motor vehicles and bicycles. Furthermore, large-sized dry lakes are excellent spots for pursuing land speed records, as the smoothness of the surface allows low-clearance vehicles to travel very fast without any risk of disruption by surface irregularities, and the path traveled has no obstacles to avoid. The dry lakes at Bonneville Salt Flats in Utah and Black Rock Desert in Nevada have both been used for setting land speed records. Dry lake beds that very rarely fill with water are sometimes used as locations for air bases, for similar reasons. Examples include Area 51 in Nevada, and Edwards Air Force Base (originally known as Muroc Dry Lake) in California.
Under United States law, a "playa lake" may be considered isolated wetlands, and may be eligible to enroll in the new wetlands component of the Conservation Reserve Program, enacted in the 2002 farm bill (P.L. 107-171, Sec. 2101).
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Devil's Golf Course in Death Valley National Park, western United States