Maʼadim Vallis is one of the largest outflow channels on Mars, about 700 km long and significantly larger than Earth's Grand Canyon. It is over 20 km wide and 2 km deep in some places. It runs from a region of southern lowlands thought to have once contained a large group of lakes (see Eridania Lake) north to Gusev crater near the equator. It looks as if water may have collected in Gusev crater, forming a giant lake; the Spirit Rover was sent there to investigate that possibility, but found only volcanic rocks on the floor of Gusev. Any lake deposits were probably covered over by a later deposit of volcanic materials from Apollinaris Mons, a nearby volcano.
Maʼadim Vallis is in the Aeolis quadrangle.
