The tortoise: The rippled surface at the top is high ground: the top of a dune. Wind pushes the ripples toward a steep sunlit slope, creating long thin, dark avalanches that slowly inch the slipface forward. At the bottom of the slope, which is shielded from winds blowing from the top, ripples have been formed by wind blowing from the left.
The hare: Oblivious to both the slow progression of ripples and dunes, 5-25 m wide dust devils have blazed on by, leaving behind erratic trails.
(HiRISE ESP_048592_2070, NASA/JPL/Univ. of Arizona)