Racetrack Playa Death Valley National Park, United States

The Racetrack Playa, or The Racetrack, is a scenic dry lake feature with sailing stones that inscribe linear racetrack imprints. It is located above the northwestern side of Death Valley, in Death Valley National Park, Inyo County, California, United States. The Racetrack Playa is 1130 m above sea level, and 4.5 km long (north-south) by 2.1 km wide (east-west). The playa is exceptionally flat and level with the northern end being only 4 cm higher than the southern.

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 Racetrack mountain area draining 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. 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 polygons that are typically 7.5 to 10 cm in diameter and about 2.5 cm thick. The polygons form in sets of three mud cracks at 120º to each other. A few days after a precipitation event, small mud curls, otherwise known as “corn flakes” form on the playa surface. Absence of these indicates that wind or another object has scraped away the tiny mud curls.
The sailing stones are a geological phenomenon found in the Racetrack. Slabs of dolomite and syenite ranging from a few hundred grams to hundreds of kilograms inscribe visible tracks as they slide across the playa surface, without human or animal intervention. The tracks have been observed and studied since the early 1900s, yet no one has seen the stones 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, in the upwards of 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.
A more recent theory is that ice collars form around rocks and the rocks along with ice are buoyantly floated off the soft bed. The minimal friction allows the rocks to be moved by arbitrarily light winds.
Two islands of bedrock outcrops rise dramatically above the playa's surface at its northern end. The larger landmark is The Grandstand, a 22 m high dark dolomite outcrop, rising in dramatic contrast from the bright white surface of the Racetrack. The second 'island' feature is a smaller carbonate outcrop.
Camping, while not allowed on the playa, is available in "primitive campsite" areas to the north and south. Visiting remote areas of Death Valley bears considerable risk. Summer temperatures can surpass 120°F (49°C), large areas are without cellphone reception, roads are treacherous and the closest gas station is in Furnace Creek.

/Wikipedia.org/

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