Out at the north end of Death Valley sits a dry lakebed called Racetrack Playa, and scattered across its cracked mud floor are rocks, some the size of a microwave, dragging long grooved trails behind them. Nobody pushed them. Nobody dragged them. For most of the twentieth century, nobody had ever actually seen one move.
People had theories for decades: wind alone, ice sheets, algae slicks, even magnetic fields. None of it was proven, because proving it meant catching several hundred pounds of rock in the act, in one of the most remote corners of one of the hottest places on the continent. That's the part that took until 2013 to solve, and it turned out to require less brute force and more sheer patience than anyone expected.
A Mystery Since the Mid-1900s
Racetrack Playa's rocks have puzzled visitors and researchers since the middle of the twentieth century. The evidence was never in question: the long, shallow grooves etched into the dried mud, sometimes running for hundreds of meters, sometimes curving or doubling back, always ending at a rock that clearly wasn't there when the track started. What was missing was the moment itself. Rocks weighing up to 700 pounds could sit motionless for years, then move, and whatever caused it never happened while a person was standing there watching.
The Slithering Stones Research Initiative
Richard Norris and James Norris, cousins working with backing from Scripps Institution of Oceanography and NASA, founded what they called the Slithering Stones Research Initiative in 2011. Their method was straightforward and slow: fit real rocks on the playa with GPS units capable of recording motion, then wait. Fifteen instrumented stones went out onto the playa, each one a real rock already sitting in its own track, now carrying a small logger that would record exactly when, how far, and how fast it moved, whenever that turned out to happen.
Richard Norris later described the odds they were working against. "We expected to wait five or 10 years without anything moving," he said, "but only two years into the project, we just happened to be there at the right time."
Plan the Drive to the Racetrack
The Racetrack sits at the end of a rough, remote road deep in Death Valley's backcountry. The trip planner can help you time it right.
Open the Trip PlannerWindowpane Ice, Not Magnetism
On December 4, 2013, and again on December 20, the team's time-lapse cameras and GPS units caught it happening. A rare combination had lined up: rain had pooled thin sheets of water across the playa, an overnight freeze turned that water into "windowpane" ice only 3 to 6 millimeters thick, and a light morning wind, around 4 to 5 meters per second, caught the floating ice panels and pushed them across the mud, shoving the embedded rocks along for the ride. Over sixty rocks moved that winter at speeds of 7 to 16 feet per minute, and some of the instrumented stones covered as much as 224 meters across multiple separate movements between December 2013 and January 2014.
- Project founded 2011
- First movement recorded DEC 4, 2013
- Ice thickness 3-6 MM
- Wind needed ~4-5 M/S
The Same Playa, Still Working
The Norris team's findings ran in the journal PLOS One in August 2014, and the mechanism they documented, ice, water, and wind acting together, is the same one that's presumably been moving these rocks for as long as the playa has existed. Nothing about the phenomenon stopped once it was explained. What has changed is how carefully the park now asks people to treat the ground it happens on. The National Park Service is direct about it: driving on the playa or anywhere off established roads is strictly prohibited, and visitors are told not to move or remove any of the rocks and to avoid walking in muddy areas when the surface is wet, since a single footprint pressed into soft playa mud can scar it for years.
Facts and figures checked against NPS.gov's own account of the moving rocks and the Norris team's 2014 findings published in PLOS One, cross-checked against Scripps Institution of Oceanography's coverage of the research.
The tracks are still out there, curving across the mud in directions no wind alone could explain until two cousins spent two winters waiting for exactly the right morning. What they caught on camera wasn't strange at all once you saw it: a sheet of ice thinner than a phone, floating just long enough to leave a groove that will outlast the ice by years. The rocks aren't moving themselves. They just found a ride nobody thought to look for.