Valles Marineris, or Mariner Valley, is a vast canyon system that runs
along the Martian equator just east of the Tharsis region. Valles Marineris is
4000 km (2500 mi) long and reaches depths of up to 7 km (4 mi)! For comparison,
the Grand Canyon in Arizona is about 800 km (500 mi) long and 1.6 km (1 mi)
deep. In fact, the extent of Valles Marineris is as long as the United States
and it spans about 20 percent (1/5) of the entire distance around
Mars! The
canyon extends from the Noctis Labyrinthus region in the west to the chaotic
terrain in the east. Most researchers agree that Valles Marineris 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. However, near the eastern flanks of the rift there appear to
be some channels that may have been formed by water.