The Racetrack Playa Mystery and Its Three-Year Solution

For most of the twentieth century, the Racetrack Playa presented a problem that no one could solve by watching. Rocks moved. Rocks weighing up to three hundred pounds crossed the flat surface of a dry lake bed in the Death Valley backcountry and left long tracks in the cracked mud, evidence of journeys that no one had ever witnessed. The tracks were real. The movement was real. The cause was not established.

The theories accumulated across decades. Wind alone, some said. Wind plus algae mats that reduced friction. Dust devils. Ice. Seismic tremors. Paranormal activity, from people who preferred that answer. None of the theories had been confirmed by direct observation, because the Racetrack is at the end of a twenty-seven-mile unpaved road, and no one had committed to being there when whatever was happening happened.

In two thousand twelve, geologist Richard Norris of the Scripps Institution of Oceanography decided to be there when it happened. His team placed GPS loggers directly on rocks and installed time-lapse cameras around the playa. Then they waited through the winters, when the playa occasionally floods and temperatures drop.

On a series of days in late twenty thirteen and early twenty fourteen, they had their answer.

Winter rain floods the playa to a shallow depth. Overnight temperatures freeze that water into thin sheets of ice. As the morning sun rises, the ice cracks and fractures into panels. Wind pushes the floating ice panels across the still-wet mud beneath them. Rocks embedded in or pushed by the leading edges of the ice panels move with the ice, too slowly to watch with the naked eye, too fast to be imaginary. The GPS logs showed rocks moving for minutes at a time, covering dozens of meters, at speeds of several meters per minute.

The mystery required the right technology, the right season, and a team willing to stake out a remote dry lake bed for three years. The solution was published in the journal PLOS ONE in August twenty fourteen.

The Racetrack is still out there, twenty-seven miles of rough road from the nearest pavement. The rocks still move in winters cold enough and wet enough to make ice. The tracks are still in the mud.