This image from the Gordii Dorsum region of Mars shows a large area covered with polygonal ridges in an almost geometric pattern.
The ridges may have originally been dunes which hardened (indurated) through the action of an unknown process. Groundwater might have been involved.
Written by: Nicolas Thomas (26 May 2010)
This is a stereo pair with ESP_018548_1910 .
More info and image formats at http://hirise.lpl.arizona.edu/ESP_017348_1910
Image: NASA/JPL/University of Arizona