The region of Mars north of the Syrtis Major volcanics and the Isidis impact basin has well-exposed bedrock with diverse compositions. These regions are dark so the colors aren’t well seen except with a sensitive imager like HiRISE and special processing.
The blue and green colors are generally due to mafic (magnesium and iron rich) minerals that are not altered by water, while the warmer colors are due to altered minerals like clays. The structure in this scene is quite complex from a combination of impact and perhaps fluvial and volcanic processes, tectonic faulting, and erosion.
The terrain is very old and has experienced a complex geologic history.
Written by: Alfred McEwen (audio by Tre Gibbs) (24 October 2012)
This is a stereo pair with ESP_028680_2070 .
More info and image formats at http://hirise.lpl.arizona.edu/ESP_028825_2070
Image: NASA/JPL/University of Arizona