Valles Marineris: The Grand Canyon of Mars . ... Credit Copyright: Viking Project , USGS , NASA Explanation: The largest canyon in the Solar System cuts a wide swath across the face of Mars. Named Valles Marineris , the grand valley extends over 3,000 kilometers long, spans as much as 600 kilometers across, and delves as much as 8 kilometers deep. By comparison, the Earth's Grand Canyon in Arizona, USA is 800 kilometers long, 30 kilometers across, and 1.8 kilometers deep. ...