Southern Oregon Coast

 Southern Oregon Coast

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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.

Geologic Background

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.

Umpqua Beach

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If you like sand dunes, this is your paradise!  The big, extensive dunes here are open to ATV's, as you can see in this photo.  Expect to see a lot of RV's with trailers full of dune buggies, side-by-sides, 4-wheelers, and motorcycles.

The source of all this sand is the several rivers along this part of the coast, particularly the Umpqua, Coos, and Coquille rivers and their tributaries.  Waves distribute that sand along the shore, mostly from north to south (the dominant storm direction averaged over the year).

Cape Arago

Cape Arago is accessed through Coos Bay and Charleston, and is one of the most scenic and interesting places on the coast.

While you're here, be sure to visit the Oregon Institute of Marine Biology in Charleston, a world-class research institution.

From Charleston, take the easy-to-find Cape Arago Highway (actually a small 2-lane road) to Sunset Beach, the lighthouse view point, Shore Acres State Park, and Cape Arago State Park.  I must say that Oregon has great state parks, and their pride in them shows!

Sunset Beach

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Sunset Beach is in a beautiful cove with a sandy beach and tide pools (my favorite part of the coast!).  The bedrock here is made of the old shoreline sandstone and siltstone layers that have been tilted by more recent tectonic compression.  You'll see this wonderful unconformity -- the boundary between the tilted layers and the younger horizontal layers.  Every unconformity tells the story of folding/tilting, erosion, and more deposition.  The horizontal layers on top were deposited at the beach, but have since been uplifted.  Wave erosion is now planing off the tilted bedrock (in the foreground), where you can browse through tide pools at low tide.

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Look closely at the tilted layers and you'll see cross-bedding that formed during deposition of sand along the ancient beach.  You can see the same kind of cross-bedding when you dig carefully into the sand on the modern beach.

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One of my daughter's first multiple syllable words as at a tide pool like this.  The one-year-old unexpectedly piped up with "sea anemone!"  Now I think of her every time I see one.

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You'll see a lot of honeycomb weathering in the sandstones.  It forms by erosion of unevenly distributed cement in the sandstone, accelerated by salt dessication.

Cape Arago Lighthouse Viewpoint

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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.

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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.

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Here's an angular unconformity, with tilted layers below and horizontal layers above.  That represents a lot of geologic time!

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Try to arrange your visits to see both high and low tides.  The tidepools are not to be missed!

Shore Acres State Park

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Shore Acres is famous for its gorgeous botanical garden.

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Take a hike down to the beach below Shore Acres for the great sand and (at low tide) tidepools.  

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Tilting of the bedrock makes this beach really interesting to see and explore!

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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.

Bandon

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Bandon 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.  

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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.

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Bandon is famous for its rocks.  Look carefully at this picture to see something most visitors miss -- the flattened bench the town is built on is roughly the same elevation as the tops of the biggest sea stacks.  That's no coincidence -- the sea stacks are remnants of the bedrock left behind by wave erosion.  The softest rocks erode fastest, while the hardest are the last ones standing.

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We made sure to visit the Bandon beaches at both low and high tides.  Low tide allows you to wander around the sea stacks to explore their crevasses and caves.

The Bandon Rocks

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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.

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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.

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Here's a block of another ocean floor rock, banded chert.

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This is a piece of greenstone, which is oceanic crust metamorphosed to a lesser degree than blueschist.

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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.

Caves and arches form where waves exploit a weakness in the rock, like fractures or weaker rock.

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Blueschist with bands of greenstone.

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I really like the red chert found along this beach.  The red is usually a bit of iron staining inside the rock.

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This blueschist is folded, showing how the subduction zone shears the rocks.

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Driftwood is another Bandon specialty.  It's all piled at the strand line, which is the high storm line.  This is looking at Coquille Point.

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Bandon Rock has a couple of nice sea arches that waves crash through.

The Coquille River Lighthouse and Jetties

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To a geologist like me, the best thing about the Bandon jetties is that they're made almost entirely of blueschist!

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Here's a look from the south jetty over to the lighthouse on the north jetty.

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Here's a very happy Roc Doc among his favorites, blueschist.

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In recent years, home construction has been allowed in the lower parts of Bandon near the harbor.  Before you think that would be an ideal place for a vacation house, consider that destruction by tsunami is inevitable.

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Bandon sunset where a creek finds the ocean.

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Take a side trip to see some cranberry fields!  These are off Randolph Road north of Bandon off Highway 101.

Cape Blanco

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Cap Blanco State Park has a lighthouse and some nice hiking trails.  The bedrock here is young coastal sediments (yellowish) over older greywacke.

Port Orford

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Head out to Port Orford Heads State Park and the lifeboat station.

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Park by the Lifeboat Station to access trails out on the headlands.

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Beautiful scenery on the tectonics-formed bedrock!

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Wow, to think what adventures this boat has seen!

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Down in the town is Fort Point and the Dock Road with access to the beach.

The Coast Highway

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Between Port Orford and Gold Beach, take all the highway turn-outs for spectacular views.  The yellowish bedrock is soft, younger coastal sediments.  The older rocks are down just below sea level here.

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Wherever the older subduction zone bedrock pops to the surface, you'll see sea stacks made of greywacke or blueschist.

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Because the coast highway famously cuts through soft bedrock that is prone to landslides, you'll see mitigation measures like shotcrete (here), blankets of boulders (rip rap) to hold in soft slopes, or rock bolts in solid bedrock.

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Highway 101 makes a big inland bend to get around Humbug Mountain, the big lump on the right.  This is looking back north.

Arizona Beach

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Arizona Beach is a lovely little spot where Myrtle and Mussell creeks meet the ocean.  It has a wide beach of dark sand from the nearby greywacke bedrock.

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We spotted this little herd of coast elk by Arizona Beach after having seen many "Elk Crossing" signs.

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Just another great Oregon beach, viewed from another highway pull-out.

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Looking back north toward distant Humbug Mountain.

Gold Beach

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There was evidently a small gold rush when someone found a little gold in the sand near here, but that's all it took for the name to stick.  This is the Wedderburn Bridge over the Rogue River.

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The harbor entrance had some good waves on this windy day!

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South of Gold Beach at Cape Sebastian.

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Looking back north at Cape Sebastian from near Patrick Creek.

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That's what the Coast Highway is all about!

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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.

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The bedrock here is mostly greywacke, so the beach sand is dark.

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View from another great highway pull-out.

Chrissy State Beach

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The 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.

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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.


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