Geologic map of the Phaethontis Quadrangle of Mars

The Phaethontis quadrangle of Mars is dominated by densely cratered uplands and plateaus which form some of the oldest surfaces on the planet. Extensive low-lying areas within the cratered terrains, including the floors of the large craters, are covered to different degrees by plains-forming material. The youngest plains unit surround Tharsis Montes to the north. Various erosional processes, including eolian scour and possibly scarp retreat through volatile-release sapping and mass wasting, producing several distinctive physiographic features: knob and mesa terrains, plains and small knobs, and plateaus dissected by furrows, steep walled gorges, and pits.