Southern Oregon Coast
Southern Oregon Coast
Take one of America's great road trips!
What You'll See
The southern Oregon coast has not only fantastic scenery, but fascinating geology as well. It was formed by tectonic plate collisions from tens of millions of years ago right up to today, and I'll show you what to look for.
The many famous sea stacks (the big rocks out in the waves) are metamorphic and sedimentary rocks formed in the subduction zone (where the Pacific plate dived under North America), and as such are uniquely beautiful and interesting. I'll show you what they are and how they formed.
This trip shows favorite scenic and geologic sites beginning at Umpqua Beach and going south to the California border.
Interactive Google Map centered on Umpqua Beach. You can pan and zoom to follow the rest of the trip.
The Pacific Plate and its ancestors have been subducting under the west coast of North America for over 200 million years. During that time, most of Washington, Oregon, and northern California were added to the continent as islands, volcanoes, small continents, and miscellaneous ocean floor rocks were scraped off the oceanic plate and plastered onto the continental plate. In this trip, you'll see some of the results of that tectonic history.
In general, the southern Oregon coast is made of, from bottom to top, subduction zone rocks (metamorphosed oceanic crust and various sedimentary rocks), 25-45 million year old coastal sedimentary rocks, and <5 million year old soft, yellowish sediments on top of everything. In most places, you'll see at least 2 of those rock packages. The oldest oceanic rocks are the massive, dark ones that form most of the sea stacks out in the water and the dark cliffs on the shore. The sedimentary rocks are tilted layers and slabs at places like Cape Arago. The youngest rocks are easy to spot because they're mostly yellowish.
At the viewpoint, take the trails out along the cliffs for these fantastic views. Like Sunset Beach, the bedrock here is tilted ancient beach deposits.
Cape Arago Lighthouse Viewpoint
Here you can see how the flat benches above sea level formed -- by wave erosion, cutting the bedrock flat. The benches have since been uplifted, and today's ocean is working on creating new ones.
Here's an angular unconformity, with tilted layers below and horizontal layers above. That represents a lot of geologic time!
Try to arrange your visits to see both high and low tides. The tidepools are not to be missed!
Shore Acres is famous for its gorgeous botanical garden.
Shore Acres State Park
You'll see lots of these sandstone contretions in the bedrock. They are places where the cement in the rock (that holds the sand grains together) is extra strong, or has been strengthened by addition of minerals like iron.
BandonBandon is one of the more popular towns along the coast. It has great lodging, restaurants, seafood, gift shops, and a marvelous cranberry sweet shop that I highly recommend.
All along the coast highway, you'll see signs saying you're entering or leaving a tsunami danger zone. Everything within about 50 feet of sea level falls in that zone, and the risk is real. A magnitude 8 or greater quake could happen any day along the Oregon-Washington coast. Remember the 2011 tsunami in northern Japan, and how much death and destruction it wrought? A tsunami like that will happen here some day.
So just what are these hard rocks left behind by wave erosion? Many of them are blueschist as seen here and in several pictures below. Blueschist is oceanic crust that was subducted under North America by tens of kilometers, then uplifted to the surface by subsequent tectonic movement.
The Bandon Rocks
Here's a beautiful blueschist block (about 2 meters tall) that shows blue and green bands that have flowed and stretched with each other. The subduction zone is an environment of very high pressure, lots of water, and shearing that creates this unique metamorphism.
This is a piece of greenstone, which is oceanic crust metamorphosed to a lesser degree than blueschist.
Most of the big rocks at Bandon are greywacke, which is a gray to greenish sandstone made of fragments of volcanic rocks. It's only found along convergent plate boundaries, where there is a chain of volcanoes inland.
I really like the red chert found along this beach. The red is usually a bit of iron staining inside the rock.
The Coquille River Lighthouse and Jetties
To a geologist like me, the best thing about the Bandon jetties is that they're made almost entirely of blueschist!
Here's a look from the south jetty over to the lighthouse on the north jetty.
The Coast Highway
Wherever the older subduction zone bedrock pops to the surface, you'll see sea stacks made of greywacke or blueschist.
We spotted this little herd of coast elk by Arizona Beach after having seen many "Elk Crossing" signs.
Whaleshead Beach is a good stop. Don't go down the rough dirt road if it's muddy, but otherwise a front wheel drive car will make it fine despite the warning signs.
Chrissy State BeachThe last beach in Oregon on our southward trip is Chrissy State Beach. It has a visitor center and a long sandy beach -- a perfect place to spend a lazy day.
I collected some interesting plate tectonics-related rocks here including gabbro (black crystalline rock), diorite (which forms under the volcanic chain), gneiss (banded metamorphic rock), and chert.