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 2,500 miles long and reaches depths of up to 4 miles. For comparison, the Grand Canyon in Arizona is about 500 miles long and typically less than 1 mile deep. In fact, the extent of Valles Marineris is as long as the United States and it spans about 20 percent of the entire circumference of Mars. The canyon extends from the Noctis Labyrinthus region in the west to the chaotic terrain in the east. Most researchers currently think that Valles Marineris is a large "crack" or rift in the Martian crust that formed as the planet's crust and interior cooled , affected by the more buoyant crust in the Tharsis region to the west, and subsequently widened by erosion. However, near the eastern flanks of the rift there appear to be some channels that may have been formed by the flow of liquid water. This model is rendered with a 2x vertical exaggeration.
Author/Origin: Northeast Planetary Data Center, NASA RPIF System, Seth S Horowitz & Peter H. Schultz