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 and are not unique to The Racetrack. Similar rock travel patterns have been recorded in several other playas in the region but the number and length of travel grooves on The Racetrack are notable.
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.(from www.wikipedia.org)