The Racetrack Playa, or The Racetrack, is a scenic dry lake feature with "sailing stones" that leave linear "racetrack" imprints. It is located above the northwestern side of Death Valley, in Death Valley National Park.
The Racetrack Playa is 3608 feet (1130 m) above sea level, and 2.8 miles (4.5 km) long (north-south) by 1.3 miles (2 km) wide (east-west). It is also exceptionally flat and level with the northern end being only 1.5 inches (4 cm) higher than the southern. The highest point surrounding it is 5,678 feet (1731 m) high Ubehebe Peak, rising 1970 feet (571 m) above the lakebed 0.85 mile (1.37 km) to the west.
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Racetrack Playa, Death Valley[/caption]The playa is in the small Racetrack Valley endorheic basin between the Cottonwood Mountains on the east and Nelson Range to the west. During periods of heavy rain, water washes down from the mountains into the playa, forming a shallow, short-lived endorheic lake. Under the hot desert sun, the thin veneer of water quickly evaporates leaving behind a surface layer of soft slick mud. As the mud dries, it shrinks and cracks into a mosaic pattern of interlocking polygons. The shape of the shallow hydrocarbon lake Ontario Lacus on Saturn's moon Titan has been compared to that of Racetrack Playa.
Racetrack is dry for almost the entire year and has no vegetation. When dry, its surface is covered with small but firm hexagonal mud crack saucers that are typically 3 to 4 inches (7.5 to 10 cm) in diameter and about an inch (2.5 cm) thick. During the bimodal rainy season (summer and especially winter) a shallow cover of water deposits a thin layer of fine mud on and between the saucers of Racetrack. Heavier winter precipitation temporarily erases them until spring when the dry conditions cause new mud cracks to form where the old ones had been. Sandblasting wind continually helps to round the edges of exposed saucers. Annual precipitation is 3 to 4 inches (75 to 100 mm) and ice cover can be 1 to 2.5 inches (2.5 to 6.5 cm) thick. Typically only part of the playa will flood in any given year.
[youtube https://www.youtube.com/watch?v=tf8t0eo3cLQ?rel=0]
The sailing stones are a geological phenomenon found in the Racetrack. The stones slowly move across the surface of the playa, leaving a track as they go, without human or animal intervention. They have never been seen or filmed in motion. Racetrack stones only move once every two or three years and most tracks last for three or four years. Stones with rough bottoms leave straight striated tracks while those with smooth bottoms wander.
The sailing stones are most likely moved by strong winter winds, reaching 90 mph, once it has rained enough to fill the playa with just enough water to make the clay slippery. The prevailing southwest winds across Racetrack playa blow to northeast. Most of the rock trails are parallel to this direction, lending support to this hypothesis.
An alternate hypothesis builds upon the first. As rain water accumulates, strong winds blow thin sheets of water quickly over the relatively flat surface of the playa. A layer of ice forms on the surface as night temperatures fall below freezing. Wind then drives these floating ice sheets, their aggregate inertia and large area providing the necessary force required to move the larger stones. Rock trails would again remain parallel to the southwest winds. According to investigator Brian Dunning, "Solid ice, moving with the surface of the lake and with the inertia of a whole surrounding ice sheet, would have no trouble pushing a rock along the slick muddy floor." A more recent theory is that ice collars form around rocks and when the local water level rises, the rocks are buoyantly floated off the soft bed. The minimal friction allows the rocks to be moved by arbitrarily light winds.