Deep in the heart of the California desert lies one of the natural world’s most puzzling mysteries: the moving rocks of Racetrack Playa, Death Valley. These are not ordinary moving rocks that tumble down mountainsides in avalanches, are carried along riverbeds by flowing water, or are tossed aside by animals. These rocks, some as heavy as 700 pounds, are inexplicably transported across a virtually flat desert plain, leaving erratic trails in the hard mud behind them, some hundreds of yards long. They move by some mysterious force, and in the nine decades since we have known about them, no one has ever seen them move.
The floor of the playa is dried, scorched mud which has broken into perfect little octagons and pentagons and mosaic. This is as “desert” as you can get in America. It’s as flat as flat can be. With rocks which seem to move on their own. They break off the hills you see in the background. Their tracks vary in length, going every which way from zig-zags to loops; some double back on themselves. Some travel only a few feet; others go for hundreds of yards, yet they can be right next to each other, and right next to some that don’t move at all.
These sailing stones, also referred to as sliding rocks or moving rocks, are assumed to slowly move across the surface of the playa, inferred from the long tracks behind them, without human or animal intervention. They have neither been seen nor 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.
A balance of specific conditions are thought to be needed for stones to move:
A saturated yet non-flooded surface,
Thin layer of clay,
Very strong gusts as initiating force,
Strong sustained wind to keep stones going.