Sulfates are found overlying clay minerals in sediments within Columbus Crater, a depression that likely hosted a lake in the past. Sulfate salt deposits ring the crater like a bathtub ring and were deposited after the clays, as the lake dried out. The image combines information from two instruments on NASA's Mars Reconnaissance Orbiter, the Compact Reconnaissance Imaging Spectrometer for Mars and the Context Camera. (Reference: Wray et al., 2011.)