Racetrack Playa in California is a flat lake bed in the dry arid desert of Death Valley National Park. Giant stones move along the surface leaving a smooth trail in the cracked silt and clay.
When it rains (only a couple of times a year) runoff from the mountains turns the floor of the Playa into a shallow lagoon. Wind and cool temperatures freeze the surface of the water creating a thin layer of ice. The movement of the rocks is attributed to wind moving the rocks while they are embedded in a large ice sheet floating on a thin layer of water.