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Print Story about the Dancing Rocks

By Robert Evans
Smithsonian Magazine
July 1999

Heed the words of Robert Frost one day and take a road less traveled by, one that will make all the difference. Go northwest from Furnace Creek in Death Valley, between the jagged rim of the Grapevine Mountains and the peaks and canyons of the Cottonwood Range. Turn south-southwest past the vast bowl of the exploded Ubehebe Crater, and take a rocky unpaved track for twenty-five miles until you descend into a broad desert valley. Slow down now, rest your rut-and-boulder-shaken frame. Around one last bend in the water-gouged and gulleyed road, prepare for a sight the like of which you have never imagined: the tracks of the sliding rocks of Racetrack Playa, a sight unique on Earth.

Only 2.8 miles from north to south and about 1.3 miles wide, the tan-colored Racetrack is arid, devoid of vegetation, and so flat that the north end is less than two inches higher than the south. Near that north end, the Grandstand, a small island of bare rock, looms dark against its light surroundings. Dozens of rocks, some weighing hundreds of pounds, rest on the surface of the playa. Each rock is at the end of a grooved track incised into the hardened clay of what was once an ancient lakebed, now dry except for rare flooding after heavy rain that makes it dark and slick.

Tracks may be long or short, some half-a-mile, others mere tens of yards. Engraved straight as a ruler, or curving and sinuous, adjacent trails may be parallel with each other or cross and cross again. Some veer abruptly more than ninety degrees from their original route. Here and there, groups of two or three loop back on themselves, leaving trails that remind you of the paths of dancers in some stately, elegant minuet of centuries past. And like dancers, some of the rocks must have spun as they moved, leaving wide and then narrower tracks, then wide again.

The rocks themselves may be as small as a fist, or as large and blocky as an ice-chest. They weigh anywhere from a few ounces to more than seven hundred pounds. Of the 162 recorded recently on the playa, more than ninety percent fell from a bed of rock known to geologists as the Racetrack Dolomite, which forms a steep promontory at the extreme south end of the Racetrack. From that birthplace, most of the dancers on the playa have progressed to the northeast, winding and cavorting for hundreds of yards across the flat surface.

Take a walk out onto the Racetrack and you can imagine that the sun-cracked hexagons beneath your feet are the perfect cobbles on some medieval street in Europe. As you walk, your feet crunch into curled clay cereal-flakes and break a silence that is almost absolute, save for the sound of air moving past your head as you walk. And if you venture a few yards up the slopes around the Racetrack, you can trace a trail made thousands of years ago when this valley was filled by a lake, and when the indigenous people walked its shores. In the shimmering 120-degree heat of the desert summer you may still see a lake in this valley, but only as a mirage.

Since the turn of the century, prospectors, scientists, and the merely curious have traveled here to see the moving rocks and their trails. On foot or horseback, by automobile and even by aircraft-for the flat valley floor makes a perfect runway-they come from all over the world. The visitors are mystified by what they see, and guess that the rocks rolled onto the playa, or were dropped there in a fraternity prank. No one has ever seen one in motion, and only since 1948 have scientists made serious attempts to explain what makes the rocks move.

In that year, two U. S. Geological Survey geologists suggested that erratic whirlwinds known as dust-devils could have caused some of the rocks to trace serpentine paths on the playa. Dust-devils flit across the desert southwest during summer, when air heated by the hot surface rises, twisting skyward, and creating miniature but powerful tornadoes of dust that is picked up as the whirlwinds move. To create his own wind, one enterprising geologist flew a plane onto the playa in 1952, soaked the clay surface to make it slick and then made movies of rocks that he blew about in the propeller wash of his aircraft. He was mimicking in a small way what nature showed him on the Racetrack. That same year came a different suggestion, when George Stanley of Fresno State College in California mapped some parallel trails, and, knowing that ice did occasionally form during winters in the mountains, concluded that the rocks became frozen in ice-sheets that floated about on shallow water.

This served to stimulate two other geologists to try to settle the matter once and for all: Was it ice, or was it only the wind that moved the rocks? Robert Sharp of California Institute of Technology and Dwight Carey of the University of California at Los Angeles watched 30 of the rocks for seven years between 1968 and 1974. Coming back twice a year, they recorded the movements and mapped the paths of the 28 rocks that moved. As he and Carey worked, Sharp began a whimsical tradition. "The first time I visited Racetrack Playa, I was with a friend," Sharp said. "His wife Mary Ann was along. Later once we started monitoring the rocks, we found one with a beautiful trail and named this first one after her." He and Carey then named others after secretaries and laboratory assistants, all women. "Jean was my wife's name and Grace was named after my aunt," Sharp said, "who lived to be 103 years old and was one of my favorite people."

To test the ice-floe hypothesis, Sharp and Carey made a corral of stakes around some of the rocks, reasoning that ice frozen against the rocks would also be fast to the stakes, preventing any sliding or dancing. If there were no ice, any rock that moved would do so with the aid of wind alone. On two occasions, a lone rock sneaked out of the corral, leaving others still trapped. Another time, one rock joined a cluster of some others that were undisturbed. To Sharp and Carey, this indicated that although ice may play a part in some movements, it is not the only means by which Mary Ann and Jean and Grace danced their minuet on the Racetrack.

As often as they went there, Sharp and Carey never saw a rock move, nor were they able to say conclusively that wind and wind alone was the cause. In a rare bit of levity-and an expression of their frustration-Sharp and Carey wrote in the Geological Society of America Bulletin that "Some immutable law of nature probably prescribes that movements occur in the darkness of stormy moonless nights, so that even a resident observer would see newly made tracks only in the dawn of a new day."

By the middle seventies, when Sharp and Carey finished their study, the U. S. National Park Service was making serious attempts to protect the Racetrack, vulnerable to vandalism by scientists and tourists alike. Already in 1969, they had dug a ditch along the west side of the playa to prevent vehicles from driving on its surface, for tire tracks last years in the arid climate. Rangers regularly inspected the place, removing rocks that had been placed for curiosity, cleaning up debris that visitors left, including shell casings and ammunition clips. Some researchers left stakes hammered into the surface, brought in extraneous rocks, and painted or carved numbers and symbols on the original residents. The rangers noticed, too, that some of the sliding rocks had been stolen as souvenirs.

The latest research has produced two strong opinions, almost defined by the gender of the scientists. For John Reid, Jr., of Hampshire College in Amherst, Massachusetts, the rocks move in lockstep, rigid in a sheet of ice that floats on shallow water when the playa is occasionally flooded. As the ice is blown about by the wind, the rocks scrape parallel trails in the fine mud of the playa surface. Paula Messina, professor of geology at San José State University, sees the rocks, individually or in pairs and small groups, as being more free-spirited, responding to the wind across the wet and slick mud. The rocks seem to dance their individual paths, sometimes in delicate loops and twirls like performers in a minuet. Messina continued Robert Sharp's tradition of using female names as identifiers, keeping the ones he had used, and adding the names of people in her own life. This delighted Sharp. "He felt like he had found his lost children. He was just thrilled."

Between 1987 and 1994, Reid took some of his students to the Racetrack to measure the force it takes to move a rock and then calculate how much wind speed is necessary to provide that force. It was hundreds of miles per hour, far greater than was realistic. But Robert Sharp is skeptical, because the finest dust on the playa-the clay particles that are the slickest when wet-is soon blown away after it dries, and probably was not there during the experiments. The wind speeds necessary are therefore much lower.

As for the trails, Reid used a geometric way of measuring how parallel they were, reasoning that the further apart parallel tracks were, the less likely it was that the wind had formed them, and the more likely that ice slabs were involved. Seven tracks made by movements in the 1980s were very similar, as were six tracks formed in 1992-3. "For the wind to move two rocks several hundred yards apart and make exactly parallel lines," Reid says, "would be the equivalent of setting a bunch of monkeys down at typewriters and have one of them produce a Shakespearean sonnet."

Messina does not agree. In 1996, she began a complete survey and analysis of every sliding rock on the Racetrack. It was a combination of the traditional geologic methods of walking and careful observation, and modern technology: satellite-based Global Positioning System (GPS) and computer-based geographic information system (GIS). With GPS she could map all the trails quickly, and to an accuracy of less than a foot, and with the computer she was able to superimpose her maps on images of the terrain, and then integrate wind data to see how the rocks and the winds interacted.

" No one had looked at the big picture," Messina explains. "I wanted to see what the playa was saying." The playa was saying some surprising things, for although there are some parallel tracks, the vast majority are not. Pamela, Amelia and Cynthia showed the spirited moves of accomplished dancers, progressing to the northeast, then rotating, turning this way and that, back to the northwest, finally parading together to the southeast. Julie and Jacki came closer and closer in their minuet, eventually turning and twisting southeast, northwest, then southeast again, making a grand loop back to the northwest, another to the northeast, with a few quick steps and turns back and forth before parading to the southeast as Pamela, Amelia and Cynthia had done. Helen was evidently a solitary dancer, looping a complete circle first counterclockwise, then clockwise, before ending her dance in a straight path to the southeast.

" Reid's plots are remarkable. They are stunning," Messina says. "But I'm not sure you can look at only those few trails and conclude that ice is necessary for all the others. The overwhelming number of trails don't show parallelism, so you can't rule out wind alone." After studying them, Paula Messina was satisfied that the dancers had not been locked together in ice. They were too free, too idiosyncratic. And she showed that the complicated patterns were traced where strong winds from two directions merged on the playa to create dust-devils, with their powerful winds in a vortex, whirling across the playa and making the rocks dance.

Modern technology could easily resolve the controversy. Install small transmitters on the rocks to monitor their movement, and install a weather station to record the rain, the wind and the freezing of the playa. If we can track animals, we can surely track rocks. But the entire Death Valley is now a national park, an International Biosphere Reserve designated by the United Nations, and carefully protected. The regulations say there can be no "perturbation of natural features" on the Racetrack because it is a wilderness area. That means that nothing can be moved, nor anything-like markings, labels, scientific equipment-added. It belongs to everyone, not only curious scientists, although some of the other visitors are curious in their own way.

Dan Dillenges is the ranger responsible for protecting Racetrack Playa. He has worked in Death Valley since 1977, full-time since 1984, and has watched the strange behavior of people visiting the sliding rocks. Apparently, the very uniqueness and isolation of the Racetrack induce a freedom of expression that is not available in the everyday lives of many visitors. He has seen them dance around naked on the ancient lakebed. Nudity, however, is not a breach of national park rules, at least not in the naked desert. On one occasion, Dillenges heard the beating of gongs in a Tibetan religious ceremony on the Racetrack. On another, he apprehended a man who had been driving on the playa, insisting he was being chased. Shown that there was only one set of tracks on the playa, the man confessed he had not taken his medication.

The Racetrack's remoteness and smooth natural runway made it attractive for drug-dealers and their transactions. To this day, you can see the faint tracks of twin-engined aircraft on the playa, and although regular surveillance by Dillenges and his colleagues has reduced the likelihood of it being used now as a clandestine landing strip, they have to be careful. Tipped off one night that someone was taking a generator and lights up to the playa, Dillenges prepared for the worst. "It appeared to us as though they were drug-dealers," he said, but as he and another ranger sneaked closer, they were surprised to see the Grandstand illuminated by hundreds of tiny lights flicking on and off.

" The whole place lit up like a damned Christmas tree. They were all drunk, but just normal kind of folks," says Dillenges. He sobered them up by having them work all night to remove the lights and wires, and sent them on their way. Racetrack Playa is an affecting place, as Paula Messina can warrant.

" My first glimpse was one of those pivotal moments. It was so unlike anything I had ever seen before," she says. "You come around the bend in the road and you see this perfectly flat area with a mountain sticking up out of its north end. It just looks so beautiful." She was instantly captivated. "I could not believe what I was seeing," Messina says. "I had to come back and see the place again."

Both Reid and Messina plan to continue their researches, for the Racetrack draws them both. "My students and I love going out there so much that we are going back to figure out the subtler parts of the process," says Reid. And Messina hopes to show that the rocks can move in the summer storms, when no ice is possible. But if she isn't able to confirm what she believes, Messina won't mind. "I like the idea of sleuthing and trying to figure things out," she says. "But I prefer that something remain a mystery, for if you know too much, the work is no longer romantic."

Solving the mystery or not, she and Reid will separately take that road less traveled by. In the light of an ending day, they will leave the dark mass of the Grandstand fading into the long evening shadows. On the playa the rocks will sit, waiting for that combination of rain and then high wind or cold that will set them moving across the Racetrack. And out of sight of human eyes on one moonlit night, as Robert Sharp imagined, Pamela, Amelia, Cynthia, Jackie, Julie and all the others will begin the second or third movement in their elegant but mysterious minuet in the desert.

Reprinted with permission of author.