Racetrack Playa's Sailing Stone, Death Valley

Racetrack Playa is a dry lake bed in the northern reaches of Death Valley National Park, Inyo County, California, sitting at roughly 3,700 feet (1,130 meters) elevation in a narrow valley east of the Panamint Range. Its surface is a hard, level sheet of fine-grained clay that cracks into a honeycomb of polygons as it dries, broken only by scattered rocks and the long, curving tracks they leave behind — the "sailing stones" that have made this playa famous.

The moving rocks were documented as far back as 1948, and for decades their cause was debated, with wind alone the leading guess. In 2014, researchers led by Richard and James Norris finally recorded the mechanism directly: after rare winter rain pools on the playa and freezes overnight, thin sheets of ice break up as they melt, and light wind — in the 4 to 5 meters-per-second range — pushes the floating ice panels into the rocks, dragging them across the mud at speeds of only millimeters per second. Stones weighing up to 320 kilograms (about 700 pounds) have been moved this way, and the tracks curve and bend wherever the ice sheets shift direction or collide.

In this puzzle, the dark, textured boulder in the foreground and the pale ribbon of its track give sharp, high-contrast shapes to place first. The cracked clay surface filling most of the frame is the slower stretch, solved by matching the repeating polygon pattern, and the hazy mountains and blue sky along the top edge tie the piece together last.