Light and shadow play on the ridges of sand dunes that lie cloistered in an impact crater in Mars' Noachis Terra region.
"Sand dunes are among the most widespread aeolian (wind-formed) features present on Mars," write HiRISE researchers Alfred McEwen and Ginny Gulick in their description of the planet's continually morphing features. " Their spatial distribution and morphology are affected by changes in wind direction and wind strength. Patterns of dune erosion and deposition provide insight into the sedimentary history of the surrounding terrain."
Via the HiRISE Tumblr, which you should all be following.