Mariner 9's view of the "labyrinth" at the western end of Vallis Marineris on Mars. Linear graben, grooves and crater chains dominate this region, along with a number of flat-topped mesas. The image is roughly 400 km across, centered at 6 S, 105 W, at the edge of the Tharsis bulge. North is up. (Mariner 9, MTVS 4187-45).
Valles Marineris is composed of steep-walled canyons, individually measuring up to 9 km deep, 250 km wide, and 1,000 km long. They were named for Mariner 9, the Mars-orbiting spacescraft that took the first pictures of the canyons in 1971.