Terrell Johnson


On the windswept desert floor of Death Valley, there’s a place where rocks move across the ground all by themselves. No one has ever seen them move, and no one knows how they do it.

No one would know they move at all if it weren’t for the trails they leave behind in Racetrack Playa (pronounced PLY-uh), a nearly 3-mile-long stretch of flat ground in Death Valley National Park that has attracted scientists, researchers and curious observers ever since the stones were first discovered nearly a century ago.

The dried-up lakebed here, about an 80-mile drive from the park’s Furnace Creek visitor center, records the path that each stone leaves behind as it grinds its way along the earth. Some weigh as little as 25 to 30 pounds, while others weighing hundreds of pounds have been found, with trails hundreds or even thousands of feet long.

Play Video


Time Lapse of Stars in Death Valley


Though researchers have made numerous visits to the playa to study the rocks — including Joseph Crook, a prospector from Nevada who was the first to report the moving rocks in 1915, and later expeditions by geologists from the U.S. Geological Survey and UCLA in the mid-1940s, early 1950s and early 1970s — no one has come up with definitive proof of how or why they move.

“There are different theories out there and nobody knows for sure because nobody’s seen it,” said Cheryl Chipman, a spokeswoman for the park. “So all we have to go on are theories.”

The earliest hypotheses ranged from the plausible — rainstorms sweeping across Death Valley caused flash flooding on the playa, followed by intense winds that blew the rocks across the mud — to the not-so-plausible: an invisible magnetic force field, or perhaps aliens, move the rocks. (After all, the infamous Area 51 lies just across the state line in Nevada.)

The idea that the rocks are blown about by strong winds gained traction for a time in the mid-20th century, as the Racetrack Playa area often experiences strong winds, sometimes with gusts as high as 70 mph. But even gusts that strong wouldn’t be enough to move many of the rocks found on the playa, some of which weigh as much as 700 pounds.

Other geologists surmised that the rocks were simply sliding downhill by the force of gravity (at an imperceptibly glacial pace, mind you). That theory went out the window when it was discovered that the rocks are actually moving uphill — the southern end of the playa, where the rocks begin their journey, is actually a few centimeters lower than the northern end.

(MORE: The World’s Most Extreme Places: Death Valley)

In the past two decades, a pair of new theories have caught the attention of geologists: the first supposes that wind, water and bacteria form a film on the surface of the playa, which the rocks then easily slide across.

That’s the theory championed by San Jose State University professor Paula Messina in a 2004 PBS documentary titled “Life in Death Valley.” Bacteria lying dormant on the surface of the playa come alive when water sweeps across them, causing long, hair-like strands to form and create a film on the playa surface.

“If the surface is exceptionally smooth, as would be expected from a bio-geologic film, even the heaviest rocks could be propelled by a small shove of the wind,” Messina told PBS.

The second, and newer, theory — which garnered buzz around the web in mid-June — involves ice, which often forms on the playa in winter. Ice collars freeze around the rocks, making it possible for them to slide along a wet playa surface, says Johns Hopkins University professor Ralph Lorenz.

After a visit to Death Valley for an unrelated research project back in 2006, the rocks captivated his imagination. When he returned home, he scanned the scientific literature for similar cases. Boulders on Arctic beaches, he discovered, sometimes display the same ability to move on their own.

What if ice formed small “rafts” around Death Valley’s rocks too, he thought, and made it possible for them to blown easily by the wind?

To find out, he decided to test his hypothesis in his own kitchen. “I took a small rock, and put it in a piece of Tupperware, and filled it with water so there was an inch of water with a bit of the rock sticking out,” he told Smithsonian magazine. “I put it in the freezer, and that then gave me a slab of ice with a rock sticking out of it.”

Just blowing on the rocks embedded in the ice sent them skidding easily across the sand, he found, leaving a telltale trail behind. “It’s a small floating ice sheet which happens to have a keel facing down that can dig a trail in the soft mud,” he added in his interview with the magazine (and expanded on further in his own scientific paper).

As persuasive as his theory sounds, it remains unproven for the rocks on Racetrack Playa. And besides, the mystery keeps the allure of the playa alive.

“We’re not really searching for an answer — we kind of like that there is no definitive answer at the moment,” said Chipman. “Death Valley is a very magical and mysterious place, and we want to keep some things that way.”
View Larger Map

MORE FROM WEATHER.COM: Why is Death Valley So Hot?

Play Video


Why is Death Valley so Hot?