The geology of the southeast quarter of the Bone Mountain quadrangle, Oregon

• Main Author: Kent, Richard Cortland
• Format: Others
• Published: PDXScholar 1972
• Subjects: Geology > Oregon > Bone Mountain; Geology; Paleontology; Sedimentology
• Online Access: https://pdxscholar.library.pdx.edu/open_access_etds/1126; https://pdxscholar.library.pdx.edu/cgi/viewcontent.cgi?article=2125&context=open_access_etds

This thesis is a study of the geology of the southeast quarter of the Bone Mountain Quadrangle. The bedrock geology mapped includes about 56 square miles.The Klamath Mountain and Coast Range Provinces of southwestern Oregon are represented in the area. Rocks in the area include the Rogue, Dothan Riddle, Days Creek, upper member of the Umpqua and Tyee Formations. The ages of these rocks range from Late Jurassic to middle Eocene. Late Jurassic ultramafic and mafic intrusive rocks associated with the Rogue Formation occur in the Klamath Province. The metavolcanics of the Rogue Format ion and an associated linear belt of mafic intrusive rocks have been thrust northwestward over the Late Jurassic-Early Cretaceous Riddle Formation. Ultramafics occur along the fault. Graywackes, siltstones, and conglomerate lenses of the Dothan Formation have been downfaulted relative to the Rogue Formation along a southeasterly dipping fault. The Dothan Formation is steeply dipping to the southeast and contains numerous folds inclined to the northwest. The genetic relationships of faulting are problematic. The Myrtle Group conglomerates, siltstones and sandstones are greatly folded and dip to the northwest. Internal structures are intense and diagnostic fauna of Late Jurassic to Early Cretaceous age indicates separate lithologic units of shallow water deposition. Tertiary sedimentary rocks include the upper member of the Umpqua and Tyee Formations of middle Eocene age. The formations are gently dipping to the northwest with coal beds and fauna indicating a near shore depositional environment.