Upside-down craters

This image shows an area not too far south of Meridiani, the area where the mineral hematite was found on the Martian surface. In the center of the image the terrain becomes quite rugged, where a great amount of material has eroded away, leaving behind buttes and mesas. Note how some of the mesas are quite circular in morphology. This is an example of inverted terrain, in which a topographically low feature, like a crater or a trench, becomes filled in with material. Later, the surrounding terrain erodes away from the topographically low feature, while the feature protects the material filling it. Small regions of mega-ripples (a duneform) are located in some of the depressions at the center of the image.