This image covers a large crater on the Northern plains of Mars. The crater is old and has been heavily modified by ground ice processes.
The most prominent of these is the network of polygonal fractures visible throughout the image. These form when temperature changes over the course of a year cause ice in the ground to expand, contract, and break. The ground moves fractionally every time this occurs.
At the center of this image, this repetitive process has shifted boulders on the surface, causing them to line up with the fractures and form striking geometric patterns.
Written by: Colin Dundas (24 November 2010)
More info and image formats at http://hirise.lpl.arizona.edu/ESP_019711_2455
Image: NASA/JPL/University of Arizona