Valles Marineris. Artwork of an view from space of Valles Marineris (Mariner Valleys), a massive system of canyons on Mars. Valles Marineris is a massive crack in the Martian crust near the equator. The entire canyon system is some 4000 kilometres long, 200 kilometres wide and up to 7 kilometres deep. The individual canyons are many hundreds of kilometres long and are several kilometres, dwarfing similar canyons on Earth. The Martian surface has been extensively mapped by unmanned spacecraft placed in orbit around Mars. Erosion features in the landscape, and data from rovers that have been used to explore the surface, suggest that water once flowed here, shaping these canyons after their formation.