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Racetrack Playa is a seasonally dry lake (a playa) located in the northern part of the Panamint Mountains in Death Valley National Parkmarker, Californiamarker, U.S.A.marker. It is famous for 'sailing stones', rocks that mysteriously move across its surface.

Geography



The playa is nestled between the Cottonwood Mountains to the east and the Last Chance Range to the west. During periods of heavy rain, water washes down from nearby mountain slopes onto the playa, forming a shallow, short-lived lake. Under the hot Death Valley sun, the thin veneer of water quickly evaporates, leaving behind a layer of soft mud. As the mud dries, it shrinks and cracks into a mosaic of interlocking polygons.

The playa is 3608 feet (1130 m) above sea level, 2.8 miles (4.5 km) long north-south, and 1.3 miles (2 km) wide east-west. It is also exceptionally flat and level with the north end being only 1.5 inches (4 cm) higher than the south. Two islands of bedrock poke above the playa's surface at its north end:

The Grandstand rises in stark relief above the northern plain of Racetrack Playa. Alongside the western gravel road leading past the playa, the National Park Service has created a parking area with descriptive signs. A bench has been provided at this point by the Mano Seca group to allow a relaxing contemplation of the Grandstand, the Racetrack Playa and the ever changing seasonal scenery. No camping is allowed by the playa, camping is permitted to the north and south.
A late winter sunrise over the Grandstand from the Mano Seca bench.


Racetrack is dry for almost the entire year and has no vegetation on it. 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 during any given year will flood.

The highest point in the immediate area is Ubehebe Peak, itself 5,678 feet (1731 m) above sea level, a full 1970 feet (571 m) above the lakebed, and 0.85 mile (1.37 km) to its west.



Sailing stones

Sailing stone in Racetrack Playa


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 just three or four years. Stones with rough bottoms leave straight striated tracks while those with smooth bottoms wander. Stones sometimes turn over, exposing another edge to the ground and leaving a different-sized track in the stone's wake.

The sailing stones are most likely moved by strong winter winds (up to 90 mph), once it has rained enough to fill the playa with just enough water to make the clay slippery. The prevailing winds across Racetrack Playa travel blow from southwest 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 providing the necessary force required to move the larger stones. Rock trails are again expected to remain parallel to the SW winds.

However, nobody has yet secured a GPS unit on these rocks to study when they actually move.

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