The sand dunes in Kaiser Crater are partially covered with seasonal carbon dioxide ice (dry ice) in this image. The dunes are made of dark sand, showing through where the dry ice has sublimated (turned to gas) in the spring sun. The fine scale structure of the ripples on the dunes shows up highlighted by the presence or absence of the ice, and the low angle of the sun on the slope. https://photojournal.jpl.nasa.gov/catalog/PIA25181