This is Valles Marieris, and it is one of the Solar System's largest cayos. It's deeper than the Grand Cayo, and its length encircles the United States from coast to coast.
Credit: NASA
Valles Marineris is a system of canyons that runs along the Martian surface east of the Tharsis region. At more than 4,000 km long, 200 km wide and up to 7 km deep, Valles Marineris is one of the largest canyons of the Solar System, surpassed in length only by the rift valleys of the mid-ocean ridge system of Earth.
