The parial circular or ringed structure in the middle of this scene is an impact crater, approximately 3.25 kilometers (approx. 2 miles) in diameter.
Since its formation, the crater has had its southern half cut away by the formation of the gorge, called Ganges Chasma. The resulting exposure of rocks along the rim of the cliff allows planetary geologists to study a cut-away, side-view of layered rocks. This view is particularly interesting here because the rock layers of the upper plains are visible in their original form outside of the crater, and in modified form within/beneath the crater, along with structures imparted by the impact.
The floor of the crater may have been filled by lavas or other material that is more resistant to erosion than the surrounding layers, since the floor of the crater sticks out into the chasma.Written by: Ross A. Beyer (28 October 2007)
This is a stereo pair with ESP_011595_1725 .
More info and image formats at http://hirise.lpl.arizona.edu/PSP_005543_1725
Image: NASA/JPL/University of Arizona