Because these canyons are poorly linked with one another, and their floors are not a regularly graded slope, they could not have formed as water drainage features. The straight alignments of many canyon walls, and the faulting in several directions associated with Noctis Labyrinthus, combine to suggest that the Valles Marineris is composed of great rift valleys formed on the surface of a dome. At the summit of the dome, near the labyrinth, the crust was stretched in all directions to form a network of fault-bounded valleys. On the flanks of the dome, the greatest strains were concentric around the summit, giving rise to a set of radial rift valleys. The image is about 1800 km across.
North is to the top of the image.