Among the most spectacular sites on the planet are the "moving rocks" on the remote Racetrack Playa at Death Valley National Park, California. Several theories exist about how the tracks are made by the rocks. Although never witnessed or recorded, scientists believe that the stone-like lake bed fills with a thin layer of water from early winter rains that freezes over winter, trapping rocks that fall onto the playa from the nearby mountains. As the ice begins to melt, thin sheets are blown by the region's strong winds, dragging the boulders, weighing up to 80 pounds each across the now muddy surface. As the lake dries, the tracks that remain make the rocks appear as though they race each other.