Dunes on Ridges
This scene shows dark sand dunes marching over the ridges created by an alluvial (water-deposited) fan in an impact crater.
These dunes may be active today, but we haven't yet observed them at significantly different times to measure the movement. The dunes are moving from northwest (upper left) to southeast, with the steep slope facing downwind.
Image Credit: NASA/JPL-Caltech/University of Arizona