This cool picture was taken by EarthSky Facebook friend Chris Tinker, who wrote:
These are the mysterious sailing stones of a dry lake bed called the Racetrack Playa. The Racetrack is tucked between the Cottonwood Mountains to the East and Nelson Range to the West, in the West/central area of Death Valley [California].
Although nobody has ever witnessed the stones in motion, several theories exist. The most popular theory is the rocks are blown by the strong winter winds, which can reach 90mph. This wind in combination with enough rain to get the very fine silt of the lake bed to soften, creates a very low friction grease that the stones may glide on.
According to Wikipedia, these sailing stones are slabs of dolomite and syenite ranging from a few hundred grams to hundreds of kilograms. They inscribe visible tracks as they slide across the playa surface, without human or animal intervention. The tracks have been observed and studied since the early 1900s, yet no one has seen the stones in motion. Racetrack stones only move once every two or three years and most tracks last for three or four years. Stones with rough bottoms leave straight striated tracks while those with smooth bottoms wander.
Thank you for your photo Chris!