The scoured and scabby floor of Eos Chasma, located east of Valles Marineris, is covered with dunes or ripples and eroded craters. The reddish-brown color likely represents older, eroded basalt. Much of this erosion may have been accomplished by water.
An eroded crater exposes compositional differences below the surface: the bluish tones are probably fresher, boulder-rich exposures of basalt and the lighter-toned material near the base of the crater wall may have a different composition. The bottom of the crater is filled with material that is similarly-toned to the surface of Eos Chasma, and was likely eroded and transported there by the wind.
Written by: Sharon Wilson (13 May 2009)
More info and image formats at http://hirise.lpl.arizona.edu/ESP_012940_1655
Image: NASA/JPL/University of Arizona