River valley networks begin near crater rims and other high ridges and wind through the cratered landscape. Valleys in this area drained into impact craters, some of which appear to have filled with water and overflowed, forming additional deep valleys (shown by arrows) to the north.

Mars Odyssey, THEMIS; NASA/JPL/Arizona State University image
Mars Orbiter, Laser Altimeter; NASA/JPL/GSFC image