Ma'adim Vallis is one of the largest canyons on Mars, about 700 kilometers long and significantly larger than Earth's Grand Canyon. It is over 20 kilometers wide and 2 kilometers deep in some places. It runs from a region of southern lowlands thought to have once contained a large group of lakes north to Gusev crater near the equator.

Ma'adim Vallis is thought to have been carved by flowing water early in Mars' history. Some of the short narrow channels along the walls of Ma'adim are probably sapping channels . Sapping occurs when groundwater partially dissolves and undermines the rock, which collapses into debris deposits and is carried away by other erosion processes.