Noctis Labyrinthus The origin of the canyons by faulting is most apparent in Noctis Labyrinthus at the western end of Valles Marineris. Many canyons have a classic graben form, with the upland plain surface preserved on the valley floor. Other canyons are more irregular in form and have rough floor terrains, evidently the consequence of landsliding and the puzzling process of pit formation. In places it appears that surface materials have sifted downward into a gaping hole in the subsurface. The inset shows a slope covered with light albedo dunes and several small landslide lobes. The large image is about 600 km across. North is to the top of the image. [46A13-28, 47A17-28, 48A21-28, 49A22-28, 50A14-28, Inset 62A64; 7° S, 100° W]