Melas Chasma is the widest segment of Valles Marineris, the largest canyon in the Solar System. In this region, hydrated sulfate salts have been detected, and are found extensively throughout the canyon. These salt-bearing deposits likely indicate that water was present in the past.
This image shows many interesting features that are common to Melas Chasma. At the north end, we can see typical “spur and gully” (or, ridge and trough) features that also mark the rim of the Valles Marineris throughout the canyon system. [More at link]