Tharsis

The Tharsis region on Mars is an enormous volcanic upland. It contains the Tharsis Bulge, on which some of the solar system's largest volcanos are located; Olympus Mons, Pavonis Mons, Arisa Mons and Ascraeus Mons. Tharsis is located on Mars' equator, at the western end of Valles Marineris.