Sailing stones

A big boulder sticks out of the dried mud. This rock is too heavy to pick up. Yet, it has mysteriously moved. A trail shows where it moved across the dirt. 

This isn’t the only rock on the move here. Many of the rocks in this part of Death Valley in North America don’t stay in one place. Their trails crisscross the cracked mud of a dried lake. 

Some rocks move in straight lines. Some move in pairs. Others zigzag this way and that, leaving a jagged trail. How did they move? No one has ever seen it. It’s a mystery. 

Boulders mysteriously zig and zag in Death Valley, California, U.S.A.



A man takes a photograph of boulders and their trails.

for a Cause

Over the years, people have wondered what makes the rocks move. They have come up with some wild ideas. Some people think the rocks are magical. Others say pranksters secretly move the rocks.

Scientists wanted a better theory. So, they looked for some evidence.

Looking to Nature

An early theory was that gravity moves the rocks. Gravity is a force in nature. It pulls things down. Many rocks moved uphill, not downhill. So, gravity wasn’t the answer.

Another theory was that strong winds pushed the rocks. Scientists tested this theory. The tests showed that even the strongest winds in the area weren’t strong enough. They couldn’t move big boulders.

This video follows the trail made by a heavy stone.

Cold Clue

Then scientists realized an important fact. The rocks move only in winter, when this area floods. One scientist decided to study the water.

She found a slimy bacteria grew in the water. The slime made the ground slippery. On a windy day, a small wind could make the rocks slide.

An Experiment

The water gave another scientist a different idea. He knew that ice floats. Maybe ice helped the rocks move.

To test his theory, he froze a rock in a tray of water and sand. The ice lifted the rock a little bit. When he blew on the rock, it moved! It left a trail in the sand.

The bacteria and ice theories might be true. Yet no one has seen the rocks move. This mystery remains unsolved.

Scientist Ralph Lorenz stands near a flooded area of Death Valley.