Geologic map of the Valles Marineris region, Mars

The Valles Marineris region lies east of Tharsis Montes (which extend from lat 12˚ to 16˚., long 101˚ to 125˚). Part of the region is in the midst of a vast plateau bounded on the west and east by Claritas and Nectaris Fossae, respectively; the remainder extends farther east into southern Xanthe Terr and western Margaritifer Terra. Channel trends, stereophotogrammetry, and radar altimetery indicate that the surface north and east of the canyons slopes toward Chryse Planitia (centered at about lat 25˚ N., long 45˚). Within the broad Valles Marineris region, three distinct physiographic provinces are recognized (fig. 1): (1) the Noctis Labyrithus province, consisting of a high plateau cut by a network of structurally controlled troughs; (2) the Valles Marineris province, characterized by broad, linear valleys hundreds of thousands of kilometers long; (3) the eastern canyon province, containing irregular depressions as much as 900 km across. Topography has been determined from a preliminary stereophotogrammetric map having a contour interval and a precision of about 1 km (Wu and others, 1986) and from latitudinal tracks of radar altimetry have a precision of 200 m (Roth and others, 1980).