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Death Valley is a desert in the southwestern United States. In part of the desert called Racetrack Playa, there is an unusual phenomenon known as the sailing stones. The stones, which weigh up to300 kilograms, appear to shift locations occasionally, sometimes moving hundreds of meters over the course of a few months. Geologists have produced three different theories to explain the phenomenon.

One such explanation is that the stones are pushed by the wind. Scientists have recorded strong winds in the playa, and when it rains, the playa's muddy floor becomes slick and slippery. Under such conditions, powerful gusts of wind could give the stones considerable push. The reduced friction of muddy ground would then allow the stones to slide long distances Adding to the strength of this theory is the observation that the stones often travel parallel to the direction of the most common prevailing winds.

A second possible theory for the stones' movement involves ice formations. During the night, groundwater will occasionally shape and form ice sheets on the ground. The ice sheets can trap stones within them. Ice sheets that form on sloping ground can start sliding slowly down the slope. Pulled by gravity, large and thick ice sheets would be able to drag along even heavy stones trapped within them. Over time the gradual sliding movement could transport the stones great distances.

A third explanation is that people move the stones as part of an elaborate joke In recent years, there have been reports of other unusual phenomena like crop circles, which were at first hard to explain but later turned out to be the work of people playing jokes It is possible that the sailing stones have been moved around by people rather than by any natural forces.

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