HiRISE acquires many images of bedrock exposures inside impact craters, because deep bedrock may be exposed in the central uplift, or new deposits may form on the floor.
The subimage shows an enhanced-color section of the crater floor of one crater. There are layers of rock with different colors (from different minerals) exposed in places where the dark reddish wind-blown drifts have been removed.
Written by: Alfred McEwen (audio by Tre Gibbs) (3 April 2013)
More info and image formats at http://hirise.lpl.arizona.edu/ESP_031099_1355
Image: NASA/JPL/University of Arizona