Oregon Coast

One of the most significant geological sites in the Pacific Northwest: what appear to be rocks sticking up out of the water are actually the remains of a ??? tree in Sunset Bay near North Bend, OR. This partially buried stump is part of a “ghost forest”, an area where trees growing just above sea level were inundated by sudden land subsidence associated with large earthquakes along the Cascadia Subduction Zone just off-shore. Analysis of and dating of trees such as this one have revealed that large “megathrust” earthquakes are a regular occurrence in the Pacific Northwest.

Thor’s Well is an interesting site at the Cape Perpetua Scenic Area near Yachats. A 10 foot wide hole in the rocky coastline, the well connects to the open ocean via a small cave. When the tide is right, waves entering the tunnel crash against the far side of the well, leading to some impressive splashes. I’m not sure we timed it quite right, but watching the well fill and drain, and experiencing the waves crashing up against the rocks was a mesmerizing experience.

Sunset from Rockaway Beach, OR. The northern section of the Oregon Coast is characterized by long stretches of wide, sandy beach. The abundant sand comes in part from sediment brought to the ocean by the Columbia River, though the sediment supply has been reduced in recent decades with the construction of numerous large dams along the Columbia and its tributaries.

Brown pelican (Pelecanus occidentalis) and Pacific harbor seals (Phoca vitulina) on Salishan Spit near Lincoln City, Oregon

Brown pelican (Pelecanus occidentalis) and Pacific harbor seals (Phoca vitulina) on Salishan Spit near Lincoln City, Oregon

These tilted rocks at Shore Acres State Park near North Bend frequently appear in many geology textbooks. The outcrop seen here is a classic example of an “angular unconformity”, in which flat-lying sediments (upper left) overlay tilted sedimentary rocks that have been planed off by erosion. The existence of angular unconformities was one of the first key lines of evidence that the Earth is very old, as they require multiple episodes of deposition, burial, uplift, and deformation in order to form.