Sailing Stones, Racetrack Playa, Death Valley National Park, California,

Sailing stones (also known as sliding rocks, walking rocks, rolling stones, and moving rocks), are a geological phenomenon where rocks move and inscribe long tracks along a smooth valley floor without human or animal intervention. The movement of the rocks occurs when large ice sheets a few millimeters thick and floating in an ephemeral winter pond start to break up during sunny days. Frozen during cold winter nights, these thin floating ice panels are driven by wind and shove rocks at speeds up to 5 meters per minute.

Trails of sliding rocks have been observed and studied in various locations, including Little Bonnie Claire Playa in Nevada, and most famously at Racetrack Playa, Death Valley National Park, California, where the number and length of tracks are notable.The Racetrack's stones speckle the playa floor, predominantly in the southern portion. Historical accounts identify some stones around 100 m (300 ft) from shore, yet most of the stones are found relatively close to their respective originating outcrops.

Three lithologic types are identified:

1) Syenite, found most abundant on the west side of the playa;
2) Dolomite, subrounded blue-gray stones with white bands;
3) Black dolomite, the most common type, found almost always in angular joint blocks or slivers.

This dolomite composes nearly all stones found in the southern half of the playa, and originates at a steep promontory, 260 m (850 ft) high, paralleling the east shore at the south end of the playa. Intrusive igneous rock originates from adjacent slopes (most of those being tan-colored feldspar-rich syenite). Tracks are often up to 100 m (330 ft) long, about 8 to 30 cm (3 to 12 in) wide, and typically much less than 2.5 cm (1 in) deep. Most moving stones range from about 6 to 18 in (15 to 46 cm) in diameter. Stones with rough bottoms leave straight striated tracks, while those with smooth bottoms tend to wander. Stones sometimes turn over, exposing another edge to the ground and leaving a different track in the stone's wake.

Trails differ in both direction and length. Rocks that start next to each other may travel parallel for a time, before one abruptly changes direction to the left, right, or even back to the direction from which it came. Trail length also varies – two similarly sized and shaped rocks may travel uniformly, then one could move ahead or stop in its track. A balance of very specific conditions is thought to be needed for stones to move: 

- A flooded surface
- A thin layer of clay
- Wind
- Ice floes
- Warming temperatures causing ice breakup.

At Racetrack Playa, these tracks have been studied since the early 1900s, yet the origins of stone movement were not confirmed and remained the subject of research for which several hypotheses existed. However, as of August 2014, timelapse video footage of rocks moving has been published, showing the rocks moving at high wind speeds within the flow of thin, melting sheets of ice. The scientists have thus identified the cause of the moving stones to be ice shove.

The stones move only every two or three years and most tracks develop over 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 track in the stone's wake.Trails differ in both direction and length. Rocks that start next to each other may travel parallel for a time, before one abruptly changes direction to the left, right, or even back the direction it came from. Trail length also varies – two similarly sized and shaped rocks may travel uniformly, then one could move ahead or stop in its track.

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