This image covers the southern slope of an old impact crater inside a larger and still older crater, in the Martian highlands.
Valley networks are often found on the most ancient Martian terrains, suggesting that Mars was a very different world more than 3 billion years ago. There are two prominent valleys near the center of the image that merge into a single northeast-trending valley (i.e., going to the upper right; be sure to look at the map-projected images that have north up.) There are bright ripples on the floors of the valleys. Although water may have carved these valleys long ago, the ripples are much more recent features created by the wind, which is channelized by the topography.
The terrain is heavily covered by dust or other wind-blown materials, muting the underlying surface features. Bright lines behind some boulders and other topography are called wind tails and are deposited in the lee of obstacles, thereby indicating wind direction (most wind tails here seem to extend to the north-northwest from obstacles, indicating winds from the south-southeast). Small, sharp impact craters are best vsibile over the smooth mantled regions; these craters probably formed in just the past few million years, which is very recent in geologic time.Written by: Alfred (17 May 2008)
More info and image formats at http://hirise.lpl.arizona.edu/PSP_007808_1575
Image: NASA/JPL/University of Arizona