The Cebrenia quadrangle is mostly covered by the plains of eastern Utopia and western Arcadia Planitiae, which are split by the prominent, north-trending Phlegra Montes ridge belt. The south-central margin of the quadrangle includes the northern part of the Elysium rise, upon which Hecates Tholus forms a domical mountain that includes the highest point in the quadrangle, more than 8,000 m above the adjacent plains to the north. This edifice includes a series of nested summit calderas and extensive fluvial valleys (Figure 7.A). Lesser ridge and scarp systems in the plains include north-trending Phlegra Dorsa in Arcadia and northwest-trending Panchaia Rupēs and northeast-trending Cydnus Rupēs in Utopia. Several systems of sinuous channel systems, including Tinjar, Granicus, Apsus, and Hrad Valles, extend hundreds of kilometers northwestward from the Elysium rise into the deeper, central floor of Utopia basin, where the lowest regional elevations (~5,000 m below the Martian datum) occur. The most prominent crater, 100-km-diameter Mie, occurs near the quadrangle’s center. The Viking 2 landing site is more than 150 km west of Mie.

This quadrangle, most of which lies 1–3 km above datum, consists of northern and central Hesperia Planum, a wrinkle-ridged volcanic plain, bordered by the cratered highlands of Tyrrhena Terra to the west and Terra Cimmeria to the east. In the center of Hesperia Planum lies the broad Tyrrhenus Mons shield. The northern part of Hadriacus Mons and a few outer massifs of Hellas basin, Ausonia Montes, crop out in the southwest corner of the quadrangle. Herschel crater forms a 275-km-diameter double-ring impact basin along the eastern margin of the quadrangle.

Phobos is the larger of the two moons of Mars, with a mean diameter2 of about 22 km and an orbital radius of 9,376 km. Phobos orbits faster than Mars rotates, so it rises in the west and sets in the east as viewed from the planet’s surface. The low orbit has made it a target for robotic spacecraft orbiting Mars. Images show craters along with numerous grooves (Figure M.1). Explanations proposed for their origin include tidal-stress induced fracturing and secondary impacts from larger craters, such as Stickney, on Phobos. Study of recent, better-resolution images suggests that the grooves, which are absent on the trailing end of Phobos, may be chains of secondary impacts caused by debris from impacts on Mars (Murray and Heggie, 2014), or debris from impacts on Phobos that orbited the moon before impacting it (Nayak and Asphaug, 2016). Lineations within Stickney (Figure M.2) may be from landslides in the moon’s weak gravity. Study of the thermal properties of the surface may determine whether the surface material is loose or relatively coherent, as these would show different rates of heating and cooling (Figure M.3).

The Phoenicis Lacus quadrangle shows the heart of the Tharsis region that dominates the western hemisphere of Mars. Elevations are high: except for the floor of Valles Marineris, essentially the entire quadrangle lies above datum. Arsia Mons rises over 11 km from the surrounding plain and is more than 400 km across. It marks the southwest end of the northeast-trending Tharsis Montes, which also include Pavonis Mons and Ascraeus Mons (MC-9). The eastern half of the map is dominated by Syria, Sinai, and Solis Plana, high plateaus that are capped by a broad field of dozens of smaller volcanic shields. From Arsia Mons across Syria Planum the elevation is 6,000 m or more, descending to 2,000 m at the southwest corner of the map. Wrapping for 1,000 km around the north and west margin of Syria Planum is the Noctis Labyrinthus, where numerous canyons and depressions intersect in a maze-like pattern (see Figure 2.3 in Chapter 2). A large, rugged promontory, informally referred to as Claritas rise, lies along the southern margin of the quadrangle and east of Claritas Fossae (Dohm et al., 2009a). Valles Marineris extends east of Noctis Labyrinthus for several thousand kilometers (across MC-18).