This image features the north polar layered deposits. The flat tongue-shaped feature at the bottom of the image is the surface of the cap.
The bright textured region near the top of the image is polygonal ground, which is commonly found in the Martian high-latitudes. Polygonal ground formation is thought to relate to temperature cycles in ice-rich soil.
Just south of the polygonal ground, a bright layer within the cap can be seen eroding in the form of landslides, particularly near the center of the image.
The most noticeable part of the polar cap is visible in an unconformity, the horizontal break in the cap layers. An unconformity is caused by non-uniform erosion or deposition. In this case, non-uniform erosion or deposition might have occurred due to variable climate over geologic time.
Written by: Kelly Kolb (1 October 2008)
More info and image formats at http://hirise.lpl.arizona.edu/PSP_009390_2595
Image: NASA/JPL/University of Arizona