Prehistoric Nedonna ---- When Plates Collide!

PART 2

Nedonna Beach is nested along the heavily vegetated, elongated Coast Range that has a varied geologic history. Its basement was formed by a volcanic island chain that collided with North America about 50 million years ago. The ancient volcanoes form many of the scenic headlands along the coast; the origins of these mountains began approximately 40 million years ago during the Eocene age. During this time-period, sandstone and siltstone formed in the area. Additionally, igneous rocks and basalt flows combined with basaltic sandstone to create many of the mountainous formations.

The entire Oregon Coast Range is a belt of uplifted land lying along the Pacific Coast. The uplift is a result of plate convergence. About 400 km west of the Coast Range lies the spreading center, which separates the Pacific plate (which extends to just east of Japan) and the Juan de Fuca plate, which descends under the North American Plate along the Cascadia subduction zone. The Coast Range overlies the subducted Juan de Fuca plate and the lies about 150 to 200 km to the east of the Cascadia subduction zone.

The range is part of a broad, plunging structural arch of sedimentary and Tertiary volcanic strata that is being uplifted. Eocene and Miocene sections form the flanks of the uplifted sections. Some of the oldest rocks are submarine tholeiitic basalts from the Eocene era. The basalt came from the basalt flows that covered much of Oregon and originated from volcanoes in the central portion of the state. Other rocks include sandstone, mudstone, and siltstone. It was during the middle Miocene period that the range was uplifted in the broad, northeast-plunging arch.  The region seaward of the location of volcanism is referred to as the "forearc" and that the materials found in the forearc are comprised of rocks scraped off the descending subducting slab.

Now you can by a Slab of Old Fashioned Tillamook Beef Jerky!