This image looks remarkably like groves of trees growing among Martian dunes. But, the trees are an optical illusion. They are actually dark streaks of sediment on the downwind side of the dunes. They were created by escaping gas from the evaporating carbon dioxide ice below. The bottom of the ice melts into vapor and moves toward holes in the ice, carrying dark sediment along with it that is then deposited when the gas escapes.

The angle of this image of Victoria Crater reveals layering at the top of the crater walls. The pattern on the floor of the crater is made of sand dunes. Tracks from NASA’s Opportunity rover can be seen on the left side of the crater. This image was taken in July 2009 by the High Resolution Imaging Science Experiment (HiRISE) camera on NASA’s Mars Reconnaissance Orbiter.