This image features a crater at the head of Dao Vallis, one of the Martian outflow channels that drains into Hellas Basin.

The outflow channels are believed to have been sculpted by giant floods of ground water erupting from the subsurface. The crater has a series of ripples on the west side of its floor that likely formed when gravity made ice-rich material slide off the crater walls into the center.

There are several small craters visible on the larger crater’s floor. Some circular features that no longer have raised rims are probably relaxed craters. Relaxed craters are more evidence that this was once—and might still be—an ice-rich area.

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.