This image shows a mound of tilted, layered rocks exposed on the floor of Melas Chasma, the widest segment of the Valles Marineris canyon system. The portion shown above is roughly 1.6 kilometers (1 mile) wide.
At the bottom of the image is a fairly smooth surface that exposes rock layers. From this perspective, the layers have a folded appearance. Short, bright ridges superposed on top of the rock layers are likely dunes or ripples composed of wind-blown particles.
The smooth surface ends at an abrupt north-facing cliff. In the shadows of the cliff walls, more rock layers can be seen in cross section. Erosion by the wind has carved alcoves into the cliff face, from which dark fans of eroded material extend downslope to the north.
The materials making up the layers in Melas Chasma and other parts of Valles Marineris may be sediment laid down by winds or water, perhaps in ancient lakes. Alternatively, they may be layers of volcanic ash. HiRISE images are providing new insight into their origin by revealing the layer structures at unprecedented scale.
Written by: James Wray (7 July 2007)
More info and image formats at http://hirise.lpl.arizona.edu/PSP_004054_1675
Image: NASA/JPL/University of Arizona