The sight is startling. Dozens of rocks, some weighing hundreds of pounds, lie at the end of grooved tracks incised into the clay of what was once an ancient lakebed at Racetrack Playa in Death Valley. The tracks may be long or short, straight as a ruler or curved and sinuous. "Here and there, groups of two or three loop back on themselves, leaving trails that remind one of the paths of dancers in some stately, elegant minuet," says author Robert Evans. The mystery is, how do the rocks move? No one has ever seen a rock in motion on the flat surface of the playa, but since 1948, scientists have been making serious attempts to explain the phenomenon.
One of the first suggestions was wind. Maybe dust devils, erratic whirlwinds, pushed these stones. To test the wind theory, one enterprising geologist flew onto the playa and blew the rocks about in the propeller wash of his aircraft. Water seems to be a key factor. Rains turn the surface slick, probably slick enough to allow the wind to push the rocks along. Ice occasionally forms during the winter, and maybe the rocks glide about locked in ice sheets floating on shallow water. A scientist some years ago began naming them, and the tradition has continued, as will the research to try to solve the mystery of these dancing rocks.