"Dozen 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. 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 this phenomenon..."