Valles Marineris: is a vast canyon system extending over 4000km from west to east near the Martian equator.Most researchers agree that it is a large tectonic "crack" in the Martian crust, forming as the planet cooled, affected by the rising crust in the Tharsis region to the west, and subsequently widened by erosional forces. Near the eastern flanks of the rift there appear to be some channels that may have been formed by water.