Carving Ma adim Vallis . ... Credit Copyright: R. Irwin III ( CEPS/NASM ,UVa), T. Maxwell, A. Howard, R. Craddock, D. Leverington Explanation: Just as erosion from the Colorado River carved the Grand Canyon on Earth, a river of flood water may have carved Ma'adim Vallis, one of the largest canyons on Mars . ... As the largest lake spilled over the low point in its boundary a torrential flood would have moved north, along the direction indicated by the arrow, carving the sinuous Ma'adim Vallis. ...