During Nevadan orogenesis (ca. 145 m.y. ago), the Galice(?) Formation was regionally metamorphosed (greenschist facies) to phyllites and schists of the Colebrooke Formation, the Pearse Peak Diorite was emplaced, and the Port Orford-Gold Beach area, Oregon, underwent intense compressional deformation. The ancestral Klamath Mountains and Sierra Nevada became important source areas for sediments.

Eugeosynclinal conditions in coastal Oregon, however, persisted into latest Jurassic (Tithonian) time. The uppermost Jurassic Otter Point Formation (new name) includes volcanic rocks, radiolarian cherts, and many graded beds--lithologic types that are unknown in the correlative Riddle Formation. Thus, the distribution of latest Jurassic facies in southwestern Oregon was comparable with that of the coastal Franciscan and the inland "Knoxville" Formations of northern California.

Late Mesozoic eugeosynclinal conditions in southwestern Oregon were terminated by Diablan orogenesis at the end of the Jurassic (ca. 135 m.y. ago). Northwest-striking wrench faults and related folds were superimposed on the northeast-striking, Nevadan structural grain. Dioritic, gabbroic, and ultramafic bodies, including the Vondergreen Hill Peridotite (new name), were emplaced.

Tectonic lands probably rose by differential movements related to wrench faulting. Coarse gravels of the Humbug Mountain Conglomerate (new name) and, later, progressively finer sediments of the Rocky Point Formation (new name) were shed into a transgressing and deepening Early Cretaceous (Valanginian) sea.

Younger Cretaceous and Tertiary evolution of the Port Orford-Gold Beach area, although poorly documented, involved extensive fragmentation and folding of the Lower Cretaceous about north- to northeast-striking axes. Several post-Diablan orogenies affected this area, including widespread major diastrophism that began in middle and late Miocene time along the Pacific coast. The most recent phases of structural development were uplift of Pleistocene terrace deposits and faulting.

Middle Miocene(?) deposits near Port Orford perhaps represent the southern limit of the Miocene within the coastal, westward-facing Tertiary embayment centered about Newport, Oregon. The Miocene has favorable reservoir characteristics and should be a prime target for offshore exploration.