At high northern latitudes, shallow troughs in the ice-rich ground form polygonal patterns. The polygons form over many years as the near-surface ice contracts and expands seasonally.
On top of this patterned ground in this image are dunes. Loose sand and dust are blown across the hard-cemented surface until collecting and forming a dune. Streaks of dust are visible in this color subimage coming from the horns of the dunes, while the higher portion of the dune blocks the dust from being blown across the surface.
Small ripples are also visible, and the small bright spots are the remnants of the seasonal carbon dioxide polar cap that coats this area in the winter.
Written by: Candy Hansen (7 August 2008)
More info and image formats at http://hirise.lpl.arizona.edu/PSP_008839_2575
Image: NASA/JPL/University of Arizona