Today's Image of Mars is of Hebes Chasma, an enclosed trough located in the most northern part of Valles Marineris that measures nearly 8000m deep. In the center of Hebes Chasma is an 8000m high mesa (flat topped mountain) with many layered deposits. It almost rises to the same height as the terrain surrounding Hebes Chasma.
Measurements from the OMEGA spectrometer on Mars Express have shown water bearing minerals, like gypsum, in Hebes Chasma, evidence that there was once an abundance of water in the trough.
It is thought that Hebes Chasma formed because of enormous stress in the Martian crust, which resulted in a number of radial faults. This stress was likely caused by crustal uplift from the development of many volcanoes in the nearby Tharsis region.
You really need to click on this image so you can see the high resolution image from the ESA. [See their article on this image and others like it]