more interesting photos
These are of whirlwind tracks. The unusual thing to me is that the tracks haven't disturbed the dunes so their force must be very slight in the thin atmosphere. The dunes are also supposed to be formed by wind but surely the whirlwind would be stronger than normal winds. I wonder if these dunes could have been formed when the air was thicker, which may happen in times of higher axial tilt.
http://www.harmakhis.org/m1001206.jpg
http://www.harmakhis.org/m1001206b.jpg
http://www.harmakhis.org/m1001206c.jpg
http://www.harmakhis.org/m1001206d.jpg