This HiRISE image shows diverse layers in a region near Mawrth Vallis, a channel that was probably carved by water in Mars' ancient past. The color subimage shows details of layers exposed in a crater wall.
Tannish to white tones are apparent, which may be reflective of differences in mineralogy. CRISM, a spectrometer on MRO, has detected clays in Mawrth, so the layers here may be clay-rich.
Clays contain water, indicating that this region may have been wet in the past. The subimage also shows polygonal-like textures on some of the layered rock. These may be dessication polygons formed when the wet clays dried. The dark patches on the layers are sand dunes.
Photo credit: NASA/JPL/University of Arizona