Sailing Stones with exactly parallel paths - Racetrack dry lake in Death Valley (California)

Most likely the two rocks moved at the same time, encased in the same iceberg (see explication below).

Sailing stones are rocks that move in long tracks on the smooth and perfectly flat surface of a dry lake, without human or animal intervention. The rocks are most likely propelled by strong winds while entrapped in floating ice sheets (or icebergs), after winter rains flooded the dry lake and made the mud soft and slippery.

For more photos and information about the Racetrack sailing stones, go to my Sailing Stones photo series.