Graben in Memnonia Fossae (Natural Colors; credits for the additional process. and color.: Dr Paolo C. Fienga - Lunexit Team)

This HiRISE image shows a Graben (roughly 2,5 Km or 1,6 miles wide) cutting a Ridge near Memnonia Sulci, a Region of Mars West of the massive Tharsis Volcanic Province. A Graben is a Trough created when 2 normal Faults (Faults dipping at an angle, with the overhanging wall sliding downwards) opposite each other lower the block of rock in between them. They are commonly associated with the tectonically-driven extension of a region and are also found in volcanic areas. Graben occur on many planets and moons, including Earth.
In this case, the Graben (running roughly East-West, indicating extension in the North-South direction) is cutting a Ridge, showing that it is more recent. The Ridge may also be tectonic in origin, therefore representing a different epoch and different type of tectonic activity.
Relationships like this can be used to determine the sequence of events in the history of the Region. The Graben Walls can also expose the local rocks at depth; in this case there is no obvious indication of Layering.