Amazonis Planitia occupies the north-central part of the map region. The east-central and northeastern parts of the map are dominated by the western margin of Olympus Mons (MC-9) and its associated aureole deposits. This forms one of the most pronounced changes in relief in the solar system when considering a topographic transect, and involves more than 25,000 m in elevation change from the summit of the giant volcano to the regionally flat, lava-flow-covered plains of Amazonis Planitia. Olympus Mons is the only part of the quadrangle above datum. The aureole deposits, which extend up to 750 km west from the flank of the volcano and lie 1–3 km below datum, are marked by the Lycus Sulci ridge systems (see Figure 8.A), which make up broad lobes, hundreds of kilometers across. In the southern part of the map, near the highland–lowland boundary, pronounced mesas, Gordii and Eumenides Dorsa, mark the landscape. Just south of the mesas is the debouchment site of Mangala Valles (MC-16). In the southwestern part, knobby-looking terrain marks a transitional boundary that separates the northern plains, including Amazonis Planitia at –3 km to –4 km, from the cratered highlands to the south. Included in this rugged terrain, located in the west-central part of the map, is Marte Vallis, a distinct but shallow valley system that connects Elysium (MC-15) and Amazonis Planitiae.