As steady as a Rock?

 

The vast Death Valley National Monument in California is a place of extremes. Snow-capped mountains dotted with pine trees and wildflowers tower over hundreds of square miles of desert that include salt and alkali flats as well as drifting dunes. Nearly 300 feet below sea level, the valley is the lowest, driest, hottest place in the United States.

Of all the many natural wonders in the valley, the most remarkable are the stones that move. These stones litter the cracked surface of the Racetrack, a three-mile-long playa, or dried-up lake.

Ranging in size from pebbles to boulders, the stones look ordinary enough. What is curious are the long, shallow furrows trailing behind each stone. Some of the tracks are dead straight; others  zigzag or curve gently. The tracks are created as the stones move, apparently of their own accord, over the playa and often over considerable distances; some of the tracks are hundreds of feet long.

How does the stones move? Some people claim that a strange, unearthly force is responsible; some insist that there is a connection with UFOs; others believe there is a natural explanation.

Dr. Robert P. Sharp thinks he knows the secret. A professor of geology at the California Institute of Technology, Sharp made a seven-year study of the phenomenon. He selected 30 stones of different shapes and sizes, tagged and named them, and marked each one’s position with a metal stake to see if any stone moved from its original site.

All but two obliged. In just under a year, one rock moved 860 feet in several moves, and a nine ounce stone made the biggest single move of 690feet.

Sharp studied the tracks the stones had made and checked the local weather conditions at the time of each movement. He concluded that the combined forces of wind and water were responsible, a conclusion supported by the fact that the course of the tracks corresponded to the direction of the prevailing winds. The average annual rainfall in the playa is rarely more than two inches, but even a light rainfall will form a sheet of moisture over the hard clay surface, making it slick. On such a surface, one powerful gust of wind, channeled in by the surrounding mountains, is all it takes to start a stone skidding across the slippery playa as fast as three feet per second.

The stones of the Racetrack have become a great tourist attraction. Knowing how the stones move is not enough to dispel the sense of mystery and wonder that such a phenomenon instills.