It is one of Death Valley’s most intriguing geological whodunits — the sliding rocks of the Racetrack Playa.

On an ancient lakebed located on the western side of Death Valley National Park, boulders that weigh up to 700 pounds sail across the almost perfectly flat terrain, leaving grooved trails in their wake. As NATURE’s Life in Death Valley shows, each of these furrows chronicles a rock’s journey, ranging from a mere few inches to nearly 3,000 feet. Some tracks manifest in straight bold lines, while others coil back on themselves in sinuous arcs.

Despite a century of scientific investigation, this curious phenomenon has confounded the geological community and park visitors alike. To this day, no one has ever seen the rocks move. But in lieu of eyewitnesses, countless theories have been put forward over the years in an effort to explain the reasons behind the migrations.

One early suggestion was that the rocks were driven by gravity, sliding down a gradual slope over a long period of time. But this theory was discounted when it was revealed that the northern end of the playa is actually several centimeters higher than the southern end and that most of the rocks were in fact traveling uphill.

Though no one has yet been able to conclusively identify just what makes the rocks move, one woman is coming closer to solving the mystery. For the past ten years, Dr. Paula Messina, professor of geology at San Jose State University in California, has made it her quest to understand what has bewildered geologists for decades. “It’s interesting that no one has seen them move, so I am kind of sleuthing to see what’s really going on here,” says Dr. Messina.

Many scientists had dedicated much of their careers to the racing rocks, but the remoteness of the area kept their research limited in scope. No one had been able to map the complete set of trails before the advent of a quick, portable method known as global positioning. Dr. Messina was the first to have the luxury of this high technology at her fingertips.

In 1996, armed with a hand-held GPS unit, she digitally mapped the location of each of the 162 rocks scattered over the playa. “I’m very fortunate that this technology was available at about the same time the Racetrack captured my interest,” she says. “It took only ten days to map the entire network — a total of about 60 miles.” Since then, she has continued to chart the movements of each rock within a centimeter of accuracy. Walking the length of a trail, she collects the longitude and latitude points of each, which snap into a line. She then takes her data back to the lab where she is able to analyze changes in the rocks’ positions since her last visit.

She has found that two components are essential to their movement: wind and water. The fierce winter storms that sweep down from the surrounding mountains carry plenty of both.

The playa surface is made up of very fine clay sediments that become extremely slick when wet. “When you have pliable, wet, frictionless sediments and intense winds blowing through,” offers Dr. Messina, “I think you have the elements to make the rocks move.”

At an elevation of 3,700 feet, strong winds can rake the playa at 70 miles per hour. But Dr. Messina is quick to point out that sometimes even smaller gusts can set the rocks in motion. The explanation for this lies in her theory, which links wind and water with yet another element: bacteria.

After periods of rain, bacteria lying dormant on the playa begin to “come to.” As they grow, long, hair-like filaments develop and cause a slippery film to form on the surface. “Very rough surfaces would require great forces to move the lightest-weight rocks,” she says. “But 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. I think of the Racetrack as being coated by Teflon, under those special conditions.”

In science, hypotheses are often based on logic. But over the years, Dr. Messina has discovered that on the Racetrack, logic itself must often be tossed to the wind. “Some of the rocks have done some very unusual things,” she says.

In her initial analysis she hypothesized that given their weight, larger rocks would travel shorter distances and smaller, lighter rocks would sail on further, producing longer trails. It also seemed reasonable that the heavier, angular rocks would leave straighter trails and rounder rocks would move more erratically.

What she discovered surprised her. “I was crunching numbers and found that there was absolutely no correlation between the size and shape of the rocks and their trails. There was no smoking gun, so this was one of the big mysteries to me.” What appears as a very flat, uniform terrain is in fact a mosaic of microclimates. In the southeastern part of the playa, wind is channeled through a low pass in the mountains, forming a natural wind tunnel. This is where the longest, straightest trails are concentrated. In the central part of the playa, two natural wind tunnels converge from different directions, creating turbulence. It’s in this area that the rock trails are the most convoluted. “What I think is happening,” proposes Dr. Messina, “is the surrounding topography is actually what is guiding the rocks and telling them where to go.”

Some people have suggested attaching radio transmitters to the rocks or erecting cameras to catch them “in the act” in order to put an end to the speculation. But as Death Valley National Park is 95 percent designated wilderness, all research in the park must be noninvasive. It is forbidden to erect any permanent structures or instrumentation. Further, no one is permitted on the playa when it is wet because each footprint would leave an indelible scar.

As for Dr. Messina, she is content in the sleuthing. “People frequently ask me if I want to see the rocks in action and I can honestly answer that I do not,” she says. “Science is all about the quest for knowledge, and not necessarily knowing all the answers. Part of the lure of this place is its mystery. It’s fine with me if it remains that way.”

Producer: Ronnie Godeanu
Art Director: Sabina Daley
Graphic Art: Lenny Drozner
Writer: Karen de Seve
Technical Director: Brian Patrick Lee
Scientific Consultant: Gianna Savoie

Thirteen Online is a production of Thirteen/WNET New York’s Kravis Multimedia Education Center in New York City. Anthony Chapman, Director of Interactive & Broadband. Carmen DiRienzo, Vice President and Managing Director, Corporate Affairs.

© 2001 Thirteen/WNET New York

All Rights Reserved

Television Credits

A Mike Birkhead Associates Production for BBC
A Presentation of Thirteen/WNET New York

Funder Credits

Funding for the TV series NATURE is made possible in part by Park Foundation. Major corporate support is provided by Canon U.S.A., Inc., Ford Motor Company, and TIAA-CREF. Additional support is provided by the nation’s public television stations.

For those interested in the subjects shown on GRAND CANYON, we present the following Web sites. All links are valid as of May 24, 2001.

Grand Canyon @ National Geographic
http://www.nationalgeographic.com/media/books/grandcanyon/
An interactive map, facts and figures, and canyon-centered books.

Grand Canyon National Park
http://www.thecanyon.com
The area’s official site, with links to the National Park Service, local tour operators, news, and weather.

Grand Canyon Explorer
http://www.kaibab.org/
Huge, varied site with historical, geological, and travel information, photos, and links to other outdoors sites.

DesertUSA
http://www.desertusa.com/
A monthly online magazine about the American Southwest.

ParkNet
http://www.nps.gov
The homepage of the National Park Service, this is a searchable site with news, travel tips, photos, and links to every park in the system.

Print Resources

We recommend the following print articles for those interested in subjects presented on the program.

——–. “A Day in the Life of a Visitor — Year 2003.” UPLIFT AND EROSION, August 1997.

——–. “Human/Wildlife Interactions.” NATURE NOTES, Spring 1995.

Hamblin, W.K., and Laura Hamblin. “Fire and Water.” NATURAL HISTORY, September 1997, 34-41.

Hart, Stephen. “Rafting Through Time.” SCIENCE WORLD, September 2, 1997, 17-19.

Williams, Ted. “Seeking Refuge.” AUDUBON, May 1996, 34-45.

Zwinger, Ann. “A Landscape of Memory.” AUDUBON, May 1996, 30-31.

A bighorn sheep. It’s not difficult to encounter wildlife in the canyon. Mule deer, bighorn sheep, bobcats, mountain lions, and elk wander the same trails that visitors travel. Seeing animals close up in their natural habitats is breathtaking, but unfortunately, many people forget these creatures are wild. According to Elaine Leslie, a biologist at Grand Canyon National Park, run-ins with wildlife injure about 20 people each year — sometimes seriously. All it takes is a 400-pound deer striking out with a hoof or turning to take a stab with its antlers. However, the trouble begins many times when human visitors don’t respect the animals’ wildness. “I can’t tell you how many people we have who try to put their children on the backs of animals,” Leslie explains.

A bighorn sheep.

But as much as humans need to be careful about themselves, they need to keep the animals’ welfare in mind as well. Even though it’s forbidden to do so in any national park, people love to feed animals. And what creature can resist a tasty treat when it’s offered? The problems arise when the wildlife comes to depend on humans for meals. “The worst-case scenario for the animals is that they lose their ability to forage and strictly seek out handouts,” Leslie says. “We had a population of deer that developed a condition called cachexia, which is literally starving to death.” She explained that fawns acquired the behavior from their parents, never learned to feed themselves, and eventually died. Tragically, the park staff was unable to rescue this group of 30 deer.

An animal autopsy report showed something shocking: about five pounds of trash in one deer’s stomach. “Paper, candy wrappers, plastic bags. Anything associated with food,” Leslie explains. “Every single animal had trash in its stomach.” After a few months, Leslie found that deer began to migrate back into the same area, and the park launched a public awareness campaign to show what happens when visitors ignore the rules. “We have improved the health of the mule deer, and we are using that experience to make sure it doesn’t happen with our elk and bighorn sheep in the area,” Leslie says.

A downy woodpecker.

Another way humans are clashing with native wildlife is by seeing the Grand Canyon in a newly popular way: flying through the gully in a small airplane. Since the 1920s, tourists have marveled at the size of the canyon from a bird’s-eye view, but today more than 100,000 commercial flights per year echo engine sounds off the mile-high walls. While the 30 air tour operators provide a unique view for visitors, the noise pollution they create destroys the natural silence for those on the ground — including the wildlife.

In his 1996 Earth Day speech, President Clinton stated that “the intrusion of such aircraft can interfere with wildlife (including threatened and endangered species), cultural resources and ceremonies, and visitors’ enjoyment of the parks, including the ability to experience natural sounds without interruption from mechanical noise.” Ironically, his voice was temporarily drowned out by a plane as he spoke to the crowd. In 1987, Congress passed the National Parks Overflights Act to control the noise pollution situation. Years later, Congress continues to deliberate over the strictness of this law, and whether or not to make some national parks flight-free.

The Colorado is a major energy source. A journey into the Grand Canyon begins at the headwaters of the Colorado River in the Rocky Mountains. Streams of snowmelt flowing from the hills of northern Colorado collect in the great river basin, which flows another 1,400 miles or so to the Gulf of California.

The Colorado is a major energy source.

Increasingly, this river has become center stage for the ongoing conflict between conservation and development efforts. The Colorado is the major water resource for most of the southwestern United States. The Hoover Dam in Nevada, built in 1936, and the Glen Canyon Dam on the border of Utah and Arizona, constructed in 1963, transform the energy from the Colorado into hydroelectric power for Wyoming, Nevada, Colorado, Utah, Arizona, New Mexico, and California. These states also receive an allotment of water diverted by the dams and measured in acre-feet. One acre-foot equals about 326,000 gallons — enough water to take a shower every day for 17 years.

The people in the states of the lower basin alone — Arizona, New Mexico, and California — consume an average of 7.5 million acre-feet per year. While the enormous dams mean drinking water, crop irrigation, and electricity for millions of people, this heavy draw on the Colorado has dramatically changed the role the river plays in a task begun millions of years ago: dredging the Grand Canyon.

The river has been eroding the canyon for six million years.

After passing through the Glen Canyon Dam, the slowed-down Colorado enters the north end of the Grand Canyon fifteen miles downstream of the dam. Here, river rafters experience the mile-deep canyon from the bottom up. Closest to the water’s edge are layers of granite and schist (striated rock) that reveal the volcanic origins of the Colorado Plateau. Rafters heading down the gully follow the same route as the sediment and debris that are scraped off the canyon floor, giving the river its name, which is Spanish for “colored red.” But when traveling at the speed of the water, river runners’ main focus is not on the colorful name, but on avoiding collisions with boulders.

An unforgettable view. To see the Grand Canyon for the first time is an experience few people will forget. The canyon vista — with its incomprehensible size, deep color, and rich display of rock layers — is unmatched by any natural display on Earth. But while the rock formations may seem arid and lifeless, the Grand Canyon is home to an astounding variety of creatures. In its mile-deep plunge, the Grand Canyon’s terrain ranges from conifer forest to desert, with river niches in between.

These different habitats allow a great diversity of wildlife to live throughout the canyon. Looking down from the rim, you might spot a bighorn sheep casually walking up a nearly vertical grade or a chuckwalla lizard basking in the sun. At the bottom, you might catch a glimpse of the Colorado River as it rushes along the canyon floor.

The canyon is a monument to its own creation, owed mostly to the mighty Colorado River. Flowing from the Rocky Mountains to the gulf of California, the Colorado River is the carving force behind this 277-mile-long chasm. This water source is also the lifeline for the many animals that live at the base of the Canyon. From there, you can follow the 6,000-foot walls as they rise from the water, a visual chronology of the six million years it took to form the canyon.

From forest above to desert below, the Grand Canyon is made up of environments of the most extreme nature, and both resident animals and visiting humans must adapt to them. Above the canyon, floor birds and bighorn sheep enjoy life on the literal edge as sheer cliffs drop thousands of feet below. Several thousand feet down, Gila monsters hunt for Gambel’s quail nests in order to devour the eggs. Walking the canyon can be more demanding for humans than wildlife, since most visitors have never experienced this kind of dry, thin air, high altitude, and frightening vertical drop. A hike down the rocky steeps is not as easy as it looks from the top. While the rock face is a little more than one vertical mile, the walk is seven miles long.

Switchback trails take the sting out of the slope, but they lengthen the distance to your destination. Add to this a starting elevation of 9,000 feet above sea level on the North Rim (7,000 on the South Rim), and your heart might start racing rather quickly — especially on your return ascent. If you make it to the canyon floor and the river, you are still about 2,500 feet above sea level.

Water is essential — and scarce. Even though the Colorado River can flush thousands of cubic feet of water per second through the canyon, not a drop is potable. The Grand Canyon National Park Service provides water stations during the summer, but recommends that hikers take at least a gallon of water on a day hike, since the dry Arizona air can quickly draw moisture out of a body.

Online content for Grand Canyon was originally posted April 1999.