Scattered across a dry lake bed in Death Valley sit heavy rocks, some the size of microwaves, each trailing a winding track up to 300 feet long. No footprints. No tire marks. The boulders appear to have simply woken up and strolled across the desert, and for over a century, no one could explain how.

This episode is a geological detective story tracing a hundred years of sleuthing into the sailing stones of Racetrack Playa. We follow the failed theories, the named rocks, a vanishing 700-pound boulder, and the elegant Goldilocks mechanism finally caught on camera that proved nature is more poetic than any myth.

• Why the rocks move independently, crossing paths and turning at right angles, defeating simple wind and tilt theories
• Sharp and Carey's 1970s study that named rocks like Marianne and Nancy and used a rebar corral to  ...