Sand dunes are found in numerous locales on Mars. These dunes are in the North polar region. High latitude dunes are covered seasonally with carbon dioxide frost (dry ice).
The subimage shows a place where material has slipped from the crest of the dune and slid down to form a deposit at the bottom. The material may have been loosened by the activity associated with sublimation (evaporation from a solid to a gas) of seasonal frost.
Written by: Candy Hansen (14 January 2009)
More info and image formats at http://hirise.lpl.arizona.edu/PSP_010546_2615
Image: NASA/JPL/University of Arizona