Dr. Robert Sharp, a geology professor, decided to find out about these rocks. He put tags on 30 stones of different sizes and shapes, hammered spikes into the ground where the rocks were sitting, and then he studied what happened for the next seven years. Twenty eight of the stones did indeed move, sometimes more than . Dr. Sharp matched the movements with the weather and found that the rocks moved because of wind and rain. Even though Death Valley gets less than two inches of rain a year, the raindrops make the smooth clay in the dry lake bed very smooth and slippery. The wind then blows the rocks across the slippery surface, sometimes as fast as every second.