This image covers a relatively dark-toned patch of ground west of the Olympus Mons volcano. This spot is one of several dark areas in this region of Mars.
These dark spots are distinctive because much of the surrounding area appears to be covered by light-toned dust. In pre-HiRISE images, the origin of this dark spot was ambiguous. This HiRISE image reveals that the dark color is likely the result of accumulations of basaltic sand (smooth, blue-colored material in the color swath) on top of otherwise relatively dust-free bedrock.
Evidence of layering is also visible within the dark (blue) area. There are alternating bands of lighter- and darker-toned material, consistent with alternating layers of bedrock. These alternating bands are not apparent outside of the dark area. This may mean that alternating layers of bedrock only occur within the dark area, or that these bedrock layers occur throughout the region but are covered and obscured by light-toned dust outside of the dark area.
Written by: chriso (28 September 2008)
This is a stereo pair with ESP_015950_1980 .
More info and image formats at http://hirise.lpl.arizona.edu/PSP_009502_1980
Image: NASA/JPL/University of Arizona