This image shows parts of Sirenum Fossae that are southwest of Gorgonum Chaos. Some of the troughs (fossae) have gullies on their walls. Gullies are incised slope features that are thought to have formed by liquid water flowing down the slopes.

It is unknown whether the water came from the subsurface or above the surface. The plains around the troughs have a number of mesas and hills that might have formed from erosion of a once-larger rock unit. The bottom of the image shows some dark linear features which are dust devil tracks.

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.