In this beautiful VIS image, taken by the NASA - Mars Odyssey Orbiter on April, 9th, 2004, and during its 10.289th orbit around the Red Planet, we can see a small portion of the Martian Region known as Melas Chasma (---> the "Melas' Abyss"): another huge (actually Melas Chasma is the widest segment of the Great Valles Marineris Canyon System) and (always relatively speaking) flat-floored Canyon, located in in the Coprates Quadrangle of Mars, and centered at 9,8° South Latitude and 283,6° East Longitude.
Melas Chasma cuts through several Layered Deposits that are thought to be made out of Sediments which were left from an ancient Lake that resulted from the runoff of the Valley Networks to the West. However, other Theories about the origin of those Sediments include Windblown (---> such as carried by Aeolian Activities) Sediment Deposits and Volcanic Ashes.
Some support for the Theory that wants the presence, in a now far and distant past, of abundant quantities of Water inside Melas Chasma, can be found is in the discovery - carried out by the NASA - Mars Reconnaissance Orbiter - of large amounts of Hydrated Sulfates which are dispersed all over the Region. In addition, Sulfate and Iron Oxides were also found (---> discovered) by the aforementioned NASA Orbiter.
The Floor of Melas Chasma is made out of about 70% younger Massive Material, that is thought to be Volcanic Ashes whipped up by the Dominant Winds (blowing in and around Melas Chasma) into truly peculiarly-looking Aeolian Surface Seatures. Melas' Floor also contains rough Rocky and Sandy Material which might come (most likely) from the erosion (always due to Aeolian Actions) of the Canyon Walls. Last, but not least, around the Edges of Melas Chasma there is also a lot of Slide Rocky and Sandy Material.
Melas Chasma is also the deepest part of the Great Valles Marineris Canyon System, since it lays roughly 11 (eleven) Km deeper than the surrounding Surface; from the deepest point of Melas Chasma to the Outflow Channels that come out from it, there are about a 0,03° of Slopes going upward to the Northern Plains. This means that if you filled Melas Chasma with fluids (i.e.: Water), you would get a huge Lake - with a depth of about 1 Km - before said fluids would finally flow out of it, towards (and onto) the Northern Plains.
Latitude (centered): 9,9472° South
Longitude (centered): 285,9330° East
This image (which is an Original Mars Odyssey Orbiter falsely colored and Map-Projected frame published on the NASA - Planetary Photojournal with the ID n. PIA 19756) has been additionally processed, magnified to aid the visibility of the details, contrast enhanced and sharpened, Gamma corrected and then re-colorized in Absolute Natural Colors (such as the colors that a normal human eye would actually perceive if someone were onboard the NASA - Mars Odyssey Orbiter and then looked down, towards the Surface of Mars), by using an original technique created - and, in time, dramatically improved - by the Lunar Explorer Italia Team.