Cerberus Fossae

The prominent trough in this sub-image (of HiRISE image TRA_000827_1875_RED)
is a segment of the Cerberus Fossae rift system.  In geological terminology
the trough is known as a graben, or down-dropped region bounded by faults.
In this location the graben is about 300 m wide and 90 m deep.  Bright,
dust-covered, cratered plains surround the graben, and darker sediments
blanket much of its floor.  Dunes that vary in size and spacing occur
within the darker sediments, and their shapes suggest that the wind
typically blows from east to west.  Light-toned, angular boulders pepper
the darker sediments.  They have broken away from the rocky walls of the
graben and tumbled downhill.  Over time this mass wasting has caused the
cliffs to retreat, widening the trough.  The somewhat lighter patches of
cratered terrain on the graben floor were once level with the surrounding
plains, but have since been lowered by faulting.  Over time they may become
obscured or buried by the darker sediments.  High-standing ridges--remnants of
the former surface--cast jagged shadows on the floor of the graben that reveal
the rugged nature of the landscape in this region of Mars.

Images from the High Resolution Imaging Science Experiment and additional
information about the Mars Reconnaissance Orbiter are available online at: 
http://www.nasa.gov/mro or http://HiRISE.lpl.arizona.edu.

For information about NASA and agency programs on the Web, visit:
http://www.nasa.gov.

JPL, a division of the California Institute of Technology in Pasadena,
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 Corporation and is operated by the University of
Arizona.