Gullies on the northwest side of Dao Vallis, a Martian outflow channel, are the focus of this observation. The outflow channels are thought to have been carved by gigantic, ancient floods.

Gullies are largely thought to be the result of water flow, but the origin of the water is much debated. One theory proposes that melting snowpack, or a mantling (blanketing) unit, forms gullies. Such a mantling unit is visible here between some of the gullies, in the full high-resolution image. Some alcove-shaped features appear to have mantling material in them. If the mantling unit is indeed related to gully formation, then gullies are potentially forming here.

For information about NASA and agency programs on the Web, visit: http://www.nasa.gov. NASA's Jet Propulsion Laboratory, a division of the California Institute of Technology in Pasadena, Calif., manages the Mars Reconnaissance Orbiter for NASA's Science Mission Directorate, Washington. Lockheed Martin Space Systems is the prime contractor for the project and built the spacecraft. The HiRISE camera was built by Ball Aerospace and Technology Corporation and is operated by the University of Arizona. The image data were processed using the U.S. Geological Survey’s ISIS3 software.