Holden Crater was once filled by at least two different lakes. The sediments deposited in those lakes are relatively light-toned where exposed, as seen in this observation from NASA's Mars Reconnaissance Orbiter. Each layer represents a different point in time and perhaps a changing environment for Martian life, if it existed. The elongated ridges with sharp crests are sand dunes. The map is projected here at a scale of 25 centimeters (9.8 inches) per pixel. [The original image scale is 25.9 centimeters (10.2 inches) per pixel (with 1 x 1 binning); objects on the order of 78 centimeters (30.7 inches) across are resolved.] North is up. https://photojournal.jpl.nasa.gov/catalog/PIA21587