HiRISE monitors dune fields across Mars to track how they are changing.
The mobile sand also cleans dust off of the bedrock in inter-dune areas, providing good views of the bedrock structures and colors.
Here we see subtle color differences between layers, and a dense network of fractures. The dunes, in contrast, are uniformly dark and relatively blue in enhanced color (really grey but less red than the bedrock, so they appear blue here).
