Geological Chronicle
Montes Rook is a ring-shaped mountain range along the western limb of the Moon, extending across the border onto the lunar far side. The range completely encircles Mare Orientale as part of a massive impact basin feature. It is a double-ring formation composed of an outer ring 620 kilometers in diameter and an inner ring 480 kilometers across. Further out, the larger Montes Cordillera range surrounds Montes Rook, separated from it by a rugged plain.
Material excavated during the formation of Montes Rook originated from a mafic layer beneath an anorthositic zone, and many peaks within the range consist of pure anorthosite. Valleys in the gap between the inner and outer rings contain small lunar maria formed by basaltic lava deposits. One of these basaltic fills in the northeastern section of the range is named Lacus Veris.
Because of its position on the lunar limb, Montes Rook is viewed edge-on from Earth, obscuring fine surface details. In the early 1960s, William K. Hartmann and Gerard Kuiper discovered its ring shape by projecting Earth-based images onto a white globe. Several named impact craters lie within or near the range, including Kopff along the eastern inner edge, Maunder on the northern inner side, and Lowell on the far side to the northwest.