This image shows dunes on the floor of Herschel Crater. The steep faces ("slipfaces") are oriented downwind, in the direction of motion of the dunes...Sand dunes form naturally as a result of the transport of sand by the wind. The dunes in this image are somewhat crescent-shaped, but are being extended and distorted downwind and merging with nearby dunes; this complex behavior is common in dune fields on Earth.

Caption: HiRise Operations Center