Nerding out on Neahkahnie Mountain
“The Neahkahnie Mountain section of the Oregon Coast Highway provides tourists with one of the most magnificent scenic routes on the Pacific Coast, if not in the entire country.” — The Highway Magazine, 1942
Consistently ranked as one of Oregon’s best landscapes, Neahkahnie Mountain is a magical place that sits inside Oswald West State Park.
“At 1631 feet, [Neahkahnie is] the highest location directly on the Oregon coast between British Columbia and Northern California.” (Garry D. Gitzen, Francis Drake in Nehalem Bay 1579: Setting the Historical Record Straight)
So what’s the story with Neahkahnie? Where did it come from? How did it get here? What makes it so magical?
According to a 1972 article by Ernest H. Lund, an associate professor of geology at the University of Oregon:
“Neahkahnie Mountain, which rises steeply from a hilly terrain of Astoria' Formation north of Nehalem Bay, is made of coarse-textured basaltic rock that solidified at shaIIow depth in some form of igneous intrusion. The texture of the. rock is distinctly coarser than that of basalt in other headlands, and the rock is properly referred to as gabbro. Somewhat elongate in an east-west direction, the mountain terminates in a high, steep sea cliff. The slope angle of the cliff is- determined by joints that are steeply inclined seaward. As the base of the cliff is undermined by the waves, large slabs of rock break off along the joint surfaces and slide into the ocean. At the outermost point of the mountain, erosion has worked along joints in such a way that rock was removed from behind the cliff face to form a tunnel.” (The ORE BIN, Volume 34, no. 11, November 1972, p. 179).
Scientists contend that Neahkahnie Mountain was formed approximately 15-35 million years ago:
“In the northwestern part of the Oregon Coast Range, geologic mapping…together with petrographic studies and analysis of new chemical data, indicates that the sill of granophyric gabbro at Neahkahnie Mountain, its attendant dikes, and an overlying thick sequence of pillow basalt and breccia, all belong to the same magmatic episode. Regional relations show the late Miocene age of the pillow basalt sequence, and hence of the Neahkahnie sill. As the sill is almost identical petrographically and chemically with the large sills in the central part of the Oregon Coast Range, a late Miocene age is suggested for them also.” (Geological Survey Research, 1963, Thomas B. Nolan, director, p. A96)
In his 1973 master’s thesis, Frank Cressy of Oregon State University dug deep into Neahkahnie:
“Four distinct lithologic units compose the Tertiary rocks of the Neahkahnie Mountain - Angora Peak area, located along the northwest Oregon coast near the town of Nehalem. The Tertiary units are the late Oligocene to early Miocene Oswald West mudstones, the middle Miocene Angora Peak sandstone member of the Astoria Formation, and middle Miocene intrusive and extrusive rocks of the Depoe Bay Basalt. These units are unconformably overlain by Pleistocene and Recent beach and dune sands, alluvium, and tidal flat muds. The Oswald West mudstones and the Angora Peak sandstone member are informal stratigraphic units proposed in this study. The Oswald West mudstones consist of over 1600 feet of well-bedded, highly burrowed, tuffaceous siltstones and silty mudstones interbedded with minor amounts of graded turbidite sandstones and submarine slump deposits.” (“Stratigraphy and Sedimentation of the Neahkahnie Mountain - Angora Peak Area, Tillamook and Clatsop Counties, Oregon” by Frank Beecher Cressy, Jr., December 13, 1973)