A canyon system on Mars, extending more than 5,000 kilometres 3,100 miles in the east-west direction in the equatorial region. The western extremity is marked by the Noctis Labyrinthus, a complex area of fault valleys graben that cut the surface into polygonal shapes. The central section consists of several parallel canyons whose average depth is 6 kilometres. At the centre they join up with Melas Chasma, a depression 160 kilometres 100 miles across. The eastern end of the system is marked by Capri Chasma. Erosion of the canyon sides has created debris in the flat valley bottom and has revealed a layered structure in the surrounding plateau. Flow channels leading into the canyon suggest that erosion by water took place in the remote past. Valles Marineris is primarily a fault structure, thought to have been created by the uplift of the volcanic Tharsis ridge to the west.