The Argyre basin spans the west half of the quadrangle, while part of Noachis Terra, at 0–2 km elevation, lies to the east. Argyre, as deep as –3 km elevation, is the best preserved of the largest multi-ringed impact basins on Mars, and is comparable in size to the Orientale basin of the Moon. The size and number of rings in the basin, which are generally expressed by discontinuous, concentric ridges and basin-facing scarps, are debated (three to seven rings or more), owing to later modification. The most common diameter assigned to a prominent, inner ring is 800–900 km, while the entire structure may be 1800 km or more across. Valleys drain toward Argyre from the south and east, while large channels may connect Argyre to the Uzboi–Ladon–Morava (see MC-19) system to the north. Drainage into the northwestern flank of the basin from surrounding plains is blocked by concentric, broad ridges. The hummocky floor of Argyre is 3–4 km below the average terrain elevation beyond the rim (Hiesinger and Head, 2002) and includes a variety of landforms. Noachis Terra is typical of the southern cratered highlands of Mars and gives its name to the oldest period of geologic time on Mars (MC-27).