The western two-thirds of the Noachis quadrangle is dominated by the heavily cratered highlands of Noachis Terra (1–3 km elevation), which are bordered to the east by Hellas Planitia. The latter, as low as –7 km, forms the floor of the ~2,300-km-diameter Hellas basin. The highland–basin margin is marked by the arcuate Hellespontus Montes, composed of basin-ring ridge systems, hundreds of kilometers long. The southern part of the quadrangle consists of the high, ridged plains of Malea and Sisyphi Plana. Broad, lengthy but relatively subtle trough systems occur west of and concentric to Hellas basin.