Update: see JPL press release.
Gully, or ravine, landforms are commonly found in the mid-latitudes on Mars, particularly in the Southern highlands. These features typically have a broad upslope alcove, feeding into a channel and apron of debris that has been carried from above. HiRISE has discovered many examples of activity in these gullies, likely driven by seasonal carbon dioxide (dry ice) frost. Images to look for such changes have been key targets for HiRISE… [More at link]