“moving rocks” phenomenon..

A dried-up lake in Death Valley, California, is where the “moving rocks” phenomenon can be observed. 

 For decades, some force seemed to be moving huge boulders weighing up to 300 kg across the surface of the earth, leaving long furrows in the sand behind them. 

Scientists conducted observations and found that snow and rain had caused a layer of water about 7 cm thick to accumulate on the dry lake bed. At night, a frost set in and the water turned to ice. A slight breeze was enough to cause the ice to move and push the boulders along the bottom of the lake, leaving furrows in the mud. These furrows only became visible a few months later, when the lake bed dried up again.