On a perfectly flat, sun-baked lake bed in Death Valley, heavy rocks, some weighing hundreds of pounds, sit at the end of long trails scraped deep into the cracked earth. No footprints, no tire tracks, no machinery. For a century, the sailing stones of Racetrack Playa were one of geology's most stubborn mysteries: stones that apparently took a stroll whenever nobody was looking, sometimes traveling farther than a football field.

This episode follows the hundred-year stakeout that finally caught the culprit: from the first 1915 prospector's report, through the seven-year study that named rocks like Nancy (860 feet of travel at two and a half inches wide) and Karen (700 pounds, refused to budge), to the steel-rebar "jail cell" a one-pound rock casually escaped. The answer, captured at last by GPS trackers, is a slow-motion ballet of buoyant i ...