NASA The Splitting of the Dunes

The mound in the center of this Mars Reconnaissance Orbiter image appears to have blocked the path of the dunes as they marched south (north is to the left in this image) across the scene. Smaller dunes run perpendicular to some of the larger-scale dunes, probably indicating a shift in wind directions in this area. via NASA http://www.nasa.gov/image-feature/jpl/pia21572/the-splitting-of-the-dunes