Death Valley’s sailing stones slide across the desert floor on their own, leaving long trails

On a remote dry lakebed in one of the hottest places on Earth, heavy rocks trace long, curving grooves across the cracked mud, some of them running for hundreds of feet. The stones appear to travel under their own power, since no one had ever caught them in the act, and their winding trails puzzled scientists for the better part of a century. The explanation, when it finally arrived, turned out to hinge not on heat but on ice.

The Racetrack Playa and its wandering rocks

The stones sit on Racetrack Playa, a flat, dried lakebed in California’s Death Valley National Park. Hundreds of rocks are scattered across its surface, some weighing as much as 700 pounds, each trailed by a shallow track pressed into the ground behind it. The trails run in synchronized patterns, sometimes turning sharply, sometimes running parallel, as if the rocks had been dragged by an invisible hand. Because the stones can sit motionless for a decade or longer, catching one mid-journey seemed nearly impossible, and for decades no eyewitness account existed.

A mystery investigated since the 1940s

Researchers began studying the phenomenon in the 1940s, and over the years they floated a range of explanations. Some proposed hurricane-force winds strong enough to shove the rocks along. Others suggested dust devils, slippery films of algae, or thick sheets of ice that might buoy the stones and reduce friction against the mud. None of these ideas could be confirmed, in large part because the movement was so rare and unpredictable that it defied direct observation.

The breakthrough came from a team led by Scripps Institution of Oceanography paleobiologist Richard Norris, working with his cousin Jim Norris and other collaborators. Because the researchers did not expect to witness motion in person, they set up a remote monitoring system instead: a high-resolution weather station capable of recording wind gusts at one-second intervals, along with 15 rocks fitted with custom motion-activated GPS units. The park service would not allow the use of native stones, so similar rocks were brought in from outside. The experiment was installed in the winter of 2011, and then the team waited.

What the researchers finally saw

In December 2013, the Norrises arrived to find the playa covered by a shallow pond about three inches deep. Shortly afterward, the rocks began to move. According to Scripps Institution of Oceanography, the observations, published in the journal PLOS ONE in 2014, showed that the motion requires a rare and specific sequence of events rather than any single dramatic force.

First, the playa fills with water deep enough to form ice on cold nights but shallow enough to leave the rocks exposed. As nighttime temperatures drop, the pond freezes into thin sheets of what the team called windowpane ice, thin enough to move freely yet strong enough to hold together. On sunny days the ice begins to melt and break into large floating panels, which even a light breeze can push across the water. Those drifting ice sheets press against the rocks and shove them forward, carving trails in the soft mud beneath.

Gentle forces, not violent ones

The measurements overturned the more dramatic earlier theories. The rocks moved under light winds of only about 10 miles per hour, driven by ice panels less than a quarter-inch thick, far too thin to lift the stones off the ground. The stones themselves crept along at just a few inches per second, a pace so slow it is nearly imperceptible from a distance when no fixed reference point is nearby. In one recorded event, rocks spread across an area the length of three football fields began moving at once and traveled more than 200 feet before stopping.

Individual rocks stayed in motion for anywhere from a few seconds to 16 minutes, and many shifted position multiple times before coming to rest. The team even documented rock-less trails formed by grounding ice panels, marks that had previously been misread as evidence of visitors stealing stones. Over roughly two and a half months, researchers recorded five movement events, some involving hundreds of rocks.

Why the effect is so rarely seen

The conditions that set the stones in motion align only occasionally, which explains why direct sightings had never been recorded before. The National Park Service notes that the process depends on a precise balance of rain, freezing temperatures, sunlight and gentle wind, a combination that comes together only every few years. One member of the team estimated that any given rock may be moving only about one-millionth of the time, and there is evidence that such movement has grown less frequent since the 1970s as the climate has warmed and hard freezes on the playa have become less common. Visitors are asked to stay off the surface when it is wet, since footprints in the soft mud can scar the lakebed for years. Even with the mechanism now documented, the researchers noted that the very largest boulders on the playa have not been seen moving, leaving a final question about whether they travel the same way.

This article was produced with the assistance of AI and reviewed by Morning Overview editors prior to publication.

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