Almost a dune

A piece of Mars: Not all piles of windblown sand are able to form proper dunes, with a fully developed avalanche on the downwind side. Here, bluish sand tries to make its way through hilly terrain, which both traps the sand and makes it difficult for slip faces (avalanches) to form. Smaller, now stabilized dunes in the upper right were also trapped by the hills. (HiRISE ESP_030570_1440, NASA/JPL/University of Arizona)