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1 November 2018 Mountainous Section of Central Oregon Coast

Mountainous Section of Central Oregon Coast

Mountainous Section of Central Oregon Coast. This view of the Oregon coast is looking southwards from a promontory towards an eroding cliffy section that is fronted by gravel/cobble beaches and seaward small sea stacks, and growlers. Parts of the oceanic margins of the Oregon Coast Range Mountains are dominated by largely unconsolidated sedimentary rocks and basaltic intrusions such as the one here (lower foreground) that forms a large promontory that juts out into the Pacific Ocean. The Early Miocene (28.1 - 15.97 Ma) sediments along the coast are thick- to thin-bedded sandstone, conglomerate, and tuffaceous siltstone of deltaic origin. The conglomerates contain abundant clasts of pumice and dacitic volcanic rocks. The Late Eocene (37.8 - 33.9 Ma) subaerial lava flows of the promontory contain breccia of porphyritic basalt with minor basaltic andesite and dacite. The black colored gravel beaches shown here are derived from comminuted and winnowed basic rocks that are packed up against the cliff base. The back beach areas as shown here and also long the wide sandy dissipative beaches elsewhere along the coast commonly contain significant accumulations of driftwood that is mostly brought to the sea in coastal rivers that head inland in coniferous logging areas. The dark colored gravels of the berm and back beach areas provide a striking contrast with the piles of gray to white colored driftwood. Beach cusps and rip currents are also common in this type of coastal setup with gravel beaches at the foot of coastal cliffs. Recession of the shoreline has left the more resistant igneous rocks behind in the nearshore zone as small sea stacks and skerries or growlers that barely protrude above the sea surface. A sea arch and small cove is shown in the lower right hand corner of the image. This type of coast occurs in a Marine West Coast climatic regime and is typical of America's Pacific Northwest coastal region. (Photograph taken by Charles W. Finkl circa. 1963 while at Oregon State University, Corvallis, Oregon, U.S.A.)

©Coastal Education and Research Foundation, Inc. 2018
"Mountainous Section of Central Oregon Coast," Journal of Coastal Research 34(6), (1 November 2018).
Published: 1 November 2018

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