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A sliding rock and its trail cut across Racetrack Playa. Photo by Marli Miller
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The mysterious sliding rocks of
Racetrack Playa
The level surface of this parched basin provides the backdrop for one of Death Valley’s most intriguing geological puzzles, the mysterious sliding rocks of Racetrack Playa. Scattered across the extraordinarily flat surface of Racetrack Playa, far from the edges of the surrounding mountains are boulders, some up to 320 kg (705 lb), and smaller pieces of rock. Stretching behind many of the stones you'll see grooved trails. Some are short, some long, some straight, some curvy. Clearly, these rocks must gouge furrows as they slide across the playa surface, yet no living person has ever witnessed these amazing rocks move!
What makes these rocks skid as much as 880 meters (2890 ft.) across the flat playa surface? Recent scientific sleuthing provides some answers.
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Satellite image of Racetrack Playa. The Last Chance range is on the left, Cottonwood mountains to the right of the light-colored playa surface.
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The playa surface
Racetrack Playa is an almost perfectly flat dry lake bed 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.
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Polygonal mudcracks form as mud dries in Racetrack Playa. Photo by Marli Miller
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