Large impact craters rebound from the initial shock, raising deep bedrock to the surface in the central uplift of the crater.
Often this bedrock has greater compositional diversity than the surface layers, because they are from greater depths, older, jumbled, and altered, and very diverse.
Written by: Alfred McEwen (15 July 2016)
More info and image formats at http://hirise.lpl.arizona.edu/ESP_045519_1730
Image: NASA/JPL/University of Arizona