The terrain in and around the Valles Marineris varies greatly, and the basic geography can be inferred from numerous photographs of this area.
Generally, the area surrounding Valles Marineris comprises ancient plains and is relatively smooth. To the west of the Valles Marineris is the Tharsis region, an area of unusually high elevation and home to some of the largest volcanoes in the solar system. Also in this area is the Noctis Labyrinthus, a large, complex depression with smaller inter-connecting canyons and valleys that forms the 'start' of the Valles Marineris. To the north and south lie the Lunae, Ophir, Sinai, Solis and Thaumaia plains, each spanning tens of degrees of latitude (Figure 4). In the east, at the 'end' of the Valles Marineris is the Chryse Planitia, an area typified by chaotic terrain and likely an outflow area.
The canyon itself is made of up several smaller canyons, or "troughs" (Figure 4) and somewhat decrease gradually in altitude from west to east. The major canyons, or "chasmata" as they are referred to, are the Tithonium, Ius, Ophir, Candor, Melas and Coprates chamsa, with the largest being Melas followed by (in no particular order) Coprates, Candor and Ius.
Some of these troughs are 50 - 100km in width, several hundred kilometers in length and about two to eight kilometers in depth (Schultz, R.A., 1991).
Closer inspections reveal a complex system of faults and grabens, macroscopically parallel to the predominant laterality of the trough walls (Schultz, R.A., 1991). In the troughs not of the "rectangular" type (e.g. Ophir Chasma), the orientations of the slip faults of grabens in these areas are not parallel to the chaotic canyon margin, instead they parallel those faults seen in the rectangular troughs, thus implying that this area underwent deformation early on, before the canyon walls had much chance to erode (Schultz, R.A., 1991).
Some of the walls in the troughs have circular or semi-circular erosional patterns, which are believed to be the result of old craters (on the surface or buried) (Malin, M.C. and Edgett, K.S., 2000).
Another interesting point to note is that in both Coprates and Melas chasmata, the material of the canyon floor appears similar in morphology and structure to the rock from the Ophir Planum.