The Sailing Stones of Death Valley

In the remote Racetrack Playa of Death Valley, California, rocks weighing up to hundreds of pounds move across the flat desert floor, leaving long trails behind them. No one ever saw them move. The phenomenon, observed since at least 1915, puzzled scientists for nearly a century before its explanation was finally discovered.

The Phenomenon

Racetrack Playa is a dry lake bed, flat and cracked, surrounded by mountains. Scattered across its surface are rocks ranging from pebbles to boulders weighing hundreds of pounds. Behind many of these rocks extend trails in the dried mud, some stretching hundreds of feet.

The trails indicate that the rocks have moved—but how? No one had ever witnessed the movement. The rocks sit motionless for years, then apparently glide across the playa surface when no one is watching.

Early Theories

Scientists proposed various explanations. Some suggested powerful winds pushed the rocks across the slippery mud surface, but experiments showed that even hurricane-force winds couldn’t move the largest stones.

Others proposed ice sheets that formed around rocks and were then pushed by wind, carrying the rocks with them. This seemed plausible but was never observed.

Magnetic fields, seismic activity, and even aliens were suggested. The mystery attracted researchers who installed GPS units and cameras, waiting patiently for the rocks to move.

The Solution

In 2014, researchers finally observed and recorded the stones in motion. The explanation was elegant and unexpected.

During certain winter conditions, a thin layer of ice forms on the playa surface overnight. When the sun rises, the ice begins to break into sheets. Light winds push these ice sheets, which carry the rocks embedded in them. The rocks slide across the mud beneath the ice, leaving trails.

The movement is slow—inches per second—and requires specific conditions: thin ice, light wind, and enough water to create a slippery surface. This combination occurs rarely, explaining why the phenomenon had never been witnessed.

Verification

The researchers captured video of rocks moving across the playa, pushed by ice sheets under wind power. The mystery that had puzzled scientists for a century was solved.

Remaining Questions

While the general mechanism is now understood, some questions remain. A few rocks appear to have moved in ways inconsistent with the ice-and-wind model. The trails sometimes show turns and stops that are difficult to explain.

These anomalies are likely attributable to variations in conditions—shifting winds, uneven ice breakup, or changes in the mud surface. But until every case is documented, some room for mystery remains.

Assessment

The sailing stones of Death Valley represent a solved mystery—a natural phenomenon that seemed supernatural until patient scientific observation revealed its mechanism. For nearly a century, rocks moved by themselves in the desert, leaving evidence of their passage but no explanation.

The solution reminds us that the natural world contains wonders that seem impossible until understood. The rocks still sail across Racetrack Playa when conditions are right, but now we know how—even if witnessing it remains a matter of luck and patience.