Twin Trek 2019: France!

This is a “travelogue” post – more geology specific posts to follow!

My sister and I had a fantastic opportunity for out annual “Twin Trek” this year! My family was having a reunion in Ireland, so our transatlantic plane tickets were covered… it opened up a whole new continent of possibilities. I handed all the responsibility for choosing a destination over to Heather, pleading that I didn’t need such a tempting distraction while finishing my thesis. I told her that as long as I could eat pastries while sitting on rocks at some point I would be happy. She’s a gem and put together a fantastic itinerary in France! Both of us had studied abroad in the south of France in college, and she had spent a year teaching English in Normandy. This time, she decided that we would explore a beautiful region that she had briefly visited and wanted to return to – Brittany, in the northwest. We hostel-hopped from Rennes to Mont-Saint-Michel to St. Malo to the Pink Granite Coast to Finisterre, then back to Rennes and on to Paris. Being over 25 and being able to get a rental car felt so luxurious… the last time we were in France as college students we got an education in foreign public transit out of necessity.  I created an ArcGIS Online map of our route and have included a link to it below (unfortunately, free WordPress accounts can’t embed maps). I love the new watercolor base map that is available! The link is followed by screenshots.

(You can reach the map of our trip location directly at this link)

twin trek map zoomtwin trek map zoomed out

I’m looking forward to writing several posts about this trip. I’m sure the research will stretch my command of the French language in new directions, but it will be a fun scavenger hunt to see what information I can find!

  1. What geologic features allow Mont-Saint-Michel to rise above the tidal flats?
  2. Why is the granite in Ploumanac’h and the rest of the “Cote de Granit Rose” so pink?
  3. When created the spectacular white cliffs near Camaret-sur-Mer on the Presque-Isle de Crozon?
  4. Why are there so many sea caves near Morgat, also on the Presque-Isel de Crozon?

But in this post, I’ll just share the travel diary part of the story.

I was cranky, jet lagged, and hadn’t slept in 20 hours when Heather picked me up from the train station in Le Mans. I’m not sure which one of us was more frazzled – she had spent the previous few hours reintroducing herself to driving stick shift in a tiny car on tiny roads after six years driving exclusively an automatic. So as glad as we were to see each other it was a very quiet car ride to Rennes, where we checked into the hostel and went in search of Brittany’s specialty: buckwheat crepes filled with delicious things. We felt significantly better about the state of the world when our food arrived, accompanied by traditional Breton teacups of hard cider.

Rennes was a wonderful place to recover from jet lag and feel like I was truly in France. Brightly painted timber-and-plaster houses lean crookedly against each other like they’ve had too many teacups of cider and surround gothic-style churches and squares full of cafe tables. After getting lunch (crepe-wrapped sausages) at the huge Saturday market at the Place des Lices, Heather and I wandered through the shopping district to the Jardin de Thabor. Once a monastery garden, the public gardens got a scenic 19th century renovation to include paths, grottoes, a botanic garden, and a delightfully random aviary. The lawns were packed with people escaping un-airconditioned apartments to catch breezes in the shade. We parked ourselves on a shady bench by the rose garden to finish the rest of the basket of strawberries. By that time my internal clock was in revolt. I went back to the hostel to crash until Heather lured me out of the room with promises of  new kinds of crepes and a glass of rose.

The next day we set out on the Twin Trek in earnest. Heather was excited to finally see Mont-Saint-Michel in sunny weather, and I was curious as to whether it would equal the hype. It turned out that getting there early on a Sunday was a great decision – the tour buses from Paris must have been running late because there were pleasantly few other tourists there. We could really imagine that we had stepped back in time. The stories on the audioguide of the Abbey made the small fee well worth the money. There aren’t many interpretive signs to bring the impressive but stark walls of the abbey to life; the audioguide explains not only the construction of the abbey but the history that it witnessed and the lives of the religious orders that lived there. We had lunch on the ramparts beside a family of seagulls who watched us with great interest and eventual disappointment when we refused to share.

Heather and I headed back to the car once tour groups started to flood the island in earnest – the small streets were so crowded that we had trouble elbowing our way back down to the gate. We drove to the storied port town (and pirate hideout) of St. Malo, settled into the hostel, and walked down the beach’s boardwalk to find a crepe place in the historic walled city. It’s amazing – the city was 75% destroyed during WWII, but was painstakingly rebuilt stone by stone so it looks unchanged since the 1600s! We missed the last bus back to the hostel and stayed to watch the Bastille Day fireworks. The fact that the sun set at 11 pm was really throwing me off!  Especially because we had big plans for the next day – a hike from St. Malo to Port Mer along the coast.

We took the number 8 bus to the Ilots stop, and then hiked the GR (Grand Randonee) 34 to Port Mer where we caught the bus back to the hostel. We weren’t using a map, but it turns out that it was over 11 miles. It was a hot, sunny day and the coast was beautiful – all sheer cliffs, ruined castles, and sailboats tacking between tiny islands. Also, as it turned out, nude beaches. So despite the ocean views, there were some parts of the route where we chose to admire the landward side of the trail. I’ve included an interactive web map below. Although it may look like we walked on water, those parts of the route actually indicate tidal flats. There’s such a huge tidal range here! When we left at the morning the sea was a between 1/2 mile and 1/4 of a mile away from the boats stranded on the tide flats, and in the evening the boats were floating. Heather and I agree that we would recommend taking the bus one stop further to La Guimorais to get straight to the prettier parts of the hike.

(You can link directly to the interactive map here)
st malo port mer map
After a well-earned dinner and beers at Port-Mer, we took the bus back to St. Malo and slept very well that night. If you weren’t doing this hike in the summer, you’d have to go all the way to Cancale to catch a bus back to St. Malo – the bust line that serves the beaches is seasonal.

After a morning exploring the ramparts of St-Malo and hunting down ermine-themed souvenirs, we started the drive west to our next hostel in Trebeurden on the Cote de Granit Rose. Once we reached the hostel, I switched into the driver’s seat and Heather navigated us to the surreal-looking geologic destination that she had been promising me – the pink granite near Ploumanac’h. We had a leisurely happy hour, hike, and dinner while watching the sun slowly set over the Channel.


We met more opportunistic seagulls while eating our picnic dinner on the pink granite


Heather hanging out with a “chaos” of pink granite boulders in the background. The boulder had been sculpted into crazy shapes by water and wind!

The next morning, I dragged Heather out of bed bright and early so that we could go back to the geologic museum I had seen at the Maison Littorale along our hike the previous evening. It gave me plenty of material for a future blog post on the granite we were scrambling over, and the Heather bought me a lovely small piece of polished local granite from the gift shop as a birthday present. She knows me well, and yes I am literally that person who fills their suitcase with rocks. In my defense, it wasn’t much bigger that a bar of soap. The museum also had an exhibit on how the park was trying to restore vegetation, so Heather and I tried to be good stewards when we were using the boulders as adult-sized jungle gyms. There were still plenty of rocks and tide pools that we could get to appropriately! The tide pools here look different than the ones in Oregon – the coralline algae is grey instead of pink, and the predominant anemones are smooth, dark, and glossy instead of rough and green.

It was hard to drag ourselves away from that amazing coastline, but we also know we needed to make it to our next stop that night. We had lunch with the chickens at the hostel, loaded up the car, and drove a two hours to the small fishing port Cameret-sur-Mer on the Presque-Isle de Crozon. We went on a hike before dinner with a plan to explore a surrealist poet’s ruined mansion, and menhir alignment, and the Point de Pen Hir. Along the way, we stumbled across a huge complex of WWII bunkers and sobering memorials to the 638 French merchant marine ships and many Bretons lost in the war.

The next day dawned grey and cloudy, and Heather had planned for us to hike near Kerloc’h and then rent kayaks. That original plan was foiled when the boat rental shop told us that the westerly wind was too strong to rent kayaks from Kerloc’h, and so we went to Morgat on the opposite side of the Cape de Chevre where the wind was more favorable.The day was still cloudy and cool when we hauled our kayaks to the edge of the tide flats. That rental staff looked at us like we were crazy and suggested renting wetsuits, but the sun came out a few minutes after we launched! It turned into an absolutely perfect day to be on the water. The wind was still unpredictable though – one sneaker wave tossed Heather and her kayak into a complete somersault as she was pushing off from a beach, scraping up her arm and scattering her belongings across the waterline. She maintains that it was OK because getting a scar at sea ought to make her an honorary Breton pirate.

Relocating our kayak adventure to Morgat had a major unexpected silver lining: sea caves!! The coastline was steep, convoluted, and carved into fantastic arches and caverns. When the tide is high you can paddle into some of them…although the incoming tide created significant whitewater in some of them. Heather and I had a blast surfing the waves in the more exciting caves but it may not have been the smartest thing to do. When a family with small kids on the bows of their kayaks asked us where the “Devil’s Chimneys” were, we crossed our fingers behind our backs and feigned ignorance.

Th next day, the clouds of the previous day turned into genuine Breton downpours. We gave up the idea of outdoor adventures in favor of taking a bouncy ferry ride across the inlet to the huge port of Brest. Unlike Rennes, it doesn’t have that old-world scenic French flavor. It was bombed completely flat during WWII and hastily rebuilt in cubic concrete except miraculously for one thing – the ancient fort. It now houses the French naval offices and also a great maritime museum. I wish I could have teleported my dad there to enjoy the exhibit on around-the-world racing in catamarans for the Jules Verne Trophy.

The next day was pretty tame… we poked around the many art galleries in Camaret-sur-Mer, and then drove back to Rennes. The following morning we took the train to Paris to meet up with Heather’s girlfriend Elaine.

While it was relatively warm in Brittany, the “canicule” (poetic French term for heat wave) was merciless in Paris during the five days of our stay. A change from the usual atmospheric patterns caused more hot air than usual to push its way north from the Sahara into countries much worse prepared to deal with it. The daily high temperature ranged from 97 to 108 degrees F , while the average high for July is 78. This forced us to change our usual travel patterns and take a more relaxed approach to Paris than we had planned. We made it through the week with strategic applications of siestas, Orangina, and ice cream.

Over the course of the visit the three of us visited the Pantheon (mercifully cool, and with a fascinating exhibit on deaf history), the Musee d’Orsay (packed, but worthwhile for the amazing exhibit on Berthe Morisot), Sacre Coeur (overrun by tourists diverted from the closed Cathedral de Notre Dame, and quieter directly after services), Musee de Montmatre (an quiet oasis well worth the admission cost with delightful exhibits about impressionists and the neighborhood), and the Catacombs (Elaine’s favorite for the Spooky Aesthetic ™, and a standout for me for the ancient history of mining). I’ll definitely write another post about the elaborate system of mines and tombs under Paris!

On the last day of our stay, we successfully navigated a packed metro with our luggage, Heather led the way to the most well-hidden municipal bus depot I’ve ever encountered, and we headed north to meet my parents and visit my grandmother in Belgium. Thank heavens the bus was air-conditioned.


Can’t I just teleport back to Ploumanac’h?

Next up: geology posts.

After that: Ireland!


Smoked in at Crater Lake

My sister is so patient with me and my geologic pilgrimages. She spent two days in 2014 tolerating me taking selfies with every geologic contact I saw in the Grand Canyon. Last summer, the two of us hopped in the car and drove south through the wildfire smoke to another one of my bucket-list stops: Crater Lake.


I knew it was the deepest lake in the USA, but nothing really prepared me for the size of the view when we arrived at the rim of the caldera! The ferry to Wizard Island looked absurdly tiny as it cruised past, 800 ft below our feet. The lake itself covers 20 square miles – it’s large enough to swallow the entire town I’m living in.

crater lake scale2

Heather sat on a bench and befriended the ground squirrels while I spent some quality time in the geology museum carved into the side of the caldera to get my bearings.

Crater Lake was a very different landmark 7,700 years ago: it was a 12,000 foot volcano that we retroactively refer to as Mt. Mazama. Around 7,700 years ago it catastrophically blew its top, spewing 12 cubic miles of magma into the atmosphere. That’s enough ash to cover the entire state of Oregon in a layer 8 inches deep if it had settled perfectly.

crate rlake eruption volume

Once the explosive eruption had come to a close, the rim of Crater Lake stood only 8,200 feet at its highest.

The upside of that massive evisceration of the volcano, besides scenic views, is that it gives us an opportunity to see the old plumbing of Mt. Mazama up close and personal!

devil's backbone plumbing

crater lake llao rock

When we hiked up to Garfield peak, we traversed jumbled cross-sections of Mt. Mazama’s ancient eruptions.


In some places there are very obvious sloping structures where lava flowed down Mt. Mazama’s flanks (below), while other parts of the slopes are messes of lighter-colored welded ash and pumice (above).


We had fun taking perspective shots with the Phantom Ship landmark, which is the scant remnant of a fissure that was filled with lava and cooled into a more resistant fin.

Crater Lake is one of the best-appreciated geologic sites in the nation; it’s a centerpiece of scores of books and papers. Nothing I could write in this blog would come close to doing justice to all that, so I’ll keep it short! Here are some of the more noteworthy online resources I found to learn more about the park’s geology:

Ian Madin wrote a great blog post on cycling around Crater Lake at Cycle Oregon, and it includes GIS reconstructions of Mt. Mazama as well as detailed descriptions of the eruption.

The USGS created a beautiful and informative poster using the LIDAR data (super-detailed laser-measured elevation) for the park, with extensive landscape notes. Click on the link in the previous sentence to get the full-sized poster.

usgs crater lake lidar

As soon as we finished the hike up Garfield Peak the wind’s direction changed. During the day the wind blew fresh air from the west, but in the evening the wind shifted to usher in the wildfire smoke from the huge fires in northern California and southern Oregon. Wide vistas were replaced with a blanket of smoke so think that I couldn’t see my car from across the parking lot. Everything besides the road might as well not have existed as we drove cautiously northwest out of the park to head back to Corvallis.


Heather, Jo the Adventure Civic, and what would be Diamond Peak if it wasn’t shrouded in smoke.

The smoke mostly cleared by the time we reached Diamond Lake. Heather and I really wished we could blow off her flight back to the east coast to spend a few days camping here! It’s always hard dropping her off at the airport. Separating was made a bit easier when a few weeks later we got news that the whole family would be going to a reunion in Europe the next summer.  The two of us started plotting new adventures in France and Ireland!



Goodbye, OSU! It’s been great!


My thesis advisor, Dr. Michael E. Campana, and I both braved the heat and walked at graduation. He was there to hood his PhD student Dr. Maria Gibson, who did fascinating work on aquifer storage and recovery in the Yakima Basin.

I made it! On June 5th I defended my thesis, Evaluation of Compartmentalized Aquifers in the Walla Walla Subbasin of Oregon Using Isotopic and Geochemical Tracers, and on June 15 I walked across the stage in Oregon State’s 150th graduation ceremony to get my M.S. in Geography.  The past year has been a whirlwind of fieldwork, coursework, teaching, writing my thesis, and jumping through all the administrative hoops to get a diploma. While much of my free time this summer will be spoken for as I try to find a groundwater resource management job here in the PNW, I’ll also be finally writing for the blog again! Keep an eye out for:

  1. Crater Lake adventures…. from last summer. Better late than never, right?
  2. More skiing thoughts – why are Mt. Hoodoo, Haystack Butte, and Mt. Washington so close together but such different shapes?
  3. Looking to the future – This year’s Twin Trek will be in France! Heather and I are going to travel around her old haunts in Britanny and Normandy, and she has promised me adventures involving pink granite cliffs and chocolate croissants.

I added glitter to my mortarboard so my folks could find me among the 4,200 graduates. It worked pretty well!


Sisters visit South Sister (and Green Lakes)

This post covers Day 2 of the Annual Twin Camping Trip: for Day 1 check out Smith Rock Hike: Volcanic Rocks, Volcanic Heat.

twin trip locations

Heather and I woke up bright and early on a chilly morning to get a head start on the popular Green Lakes trail up to the base of South Sister, one of a trio of snow-capped volcanic peaks west of Bend. We hiked Trail 1.7 (traced in yellow on the map below), and stopped for lunch at a very scenic overlook (red dot). Including all our side jaunts, it was a 11 mile round-trip hike with about 1,000 feet of elevation gain from the trailhead to the lakes. We were three thousand feet higher here than at Smith Rock, so thankfully it was much cooler.


Fall Creek is aptly named – and it’s absolutely beautiful!



Just when the ponderosa pines and waterfalls are starting to become routine, the view opens up onto the jagged slopes of the Newberry rhyolitic dome from South Sister’s most recent eruption 2,000 years ago. Although it looks inhospitable it actually is a perfect home for a variety of adorable rodents. A little pika and several yellow-bellied marmots stuck their noses out of the rubble to say hello. Too far away to photograph, alas, you’ll just have to take our word for it. Heather said that the lava flow looked like Mordor from the Lord of the Rings… maybe a lair for the ASBOG Balrog?


Related image

Pika, photo from the National Wildlife Federation

Marmota flaviventris (Yellow Bellied Marmot), Yosemite NP - Diliff.jpg

Marmot, photo from Wikipedia

These lava flows blocked the Fall Creek drainage thoroughly enough that debris and water built up behind them, creating the spectacular Green Lakes!


Almost there…


The very top of North Sister peeked up above the flanks of South and Middle Sister in this shot


Heather contemplates how much work it would take to bring a kayak up here…

As we sat to eat lunch at the overlook we were entertained by the profanity yelled by hikers who decided to gleefully jump into Green Lake only to discover how freezing cold it is, even in August. Let’s just say that when I stuck my feet in the lake to cool off it only took about 10 seconds for them to go numb… I’m not tempted to turn that into a full-body experience.


Ultimate Sisters selfie: Heather, South Sister, and me

We were pretty beat by the time we descended back to the trailhead and happily fell into our hammocks with libations back at Elk Lake. It was another hour or two before we felt like moving again, and we made dinner with the last bits of daylight. Afterwards we took advantage of the clear skies to stargaze – Heather had never seen the Milky Way except in photos. Stupid southeast/east coast light pollution. I’m so glad we could fix that – we had an amazing view not only of our galaxy but of several shooting stars that put on a show! The next morning we packed up camp and headed out on the next adventure to an even bigger volcano: Crater Lake National Park.

But before we leave the Sisters… what were we hiking on?

All three Sisters are part of the High Cascades, the range of distinctive volcanoes in Oregon and Washington that formed between approximately 35 million years ago and the present. I gave a bit of a teaser to their history in my post about Dome Rock in the Western Cascades – I could see the Sisters from there.

Three Sisters annotated photograph viewed from south to North from Broken Top, Oregon.  (Click image to view full size.)

Three Sisters Family Portrait, from their USGS Volcanic Hazards website

The Sisters, while linked together by their names, are not triplets. North Sister is by far the eldest; it was formed between 120,000 to 45,000 years ago by basalt and andesite lavas and eruptions. Middle Sister formed between 40 and 14 thousand years ago, but primarily between 25 and 18 thousand years ago, putting it close in age with South Sister. It is built of andesite, dacite, and rhyolite, and is famous for the archaeologically significant Obsidian Cliffs formed in one of its eruptions that became a tool-making bonanza for Native Americans.

Here’s more specific timeline that I drew for South Sister, based on information from the US Geological Survey Volcanic Hazards Program (USGS VHP).

South Sister eruptive history

You can get an idea of the wide range of eruption ages in the figure below from the Oregon Department of Geology and Mineral Industries (DOGAMI)’s recreation brochure for the area.

DOGAMI eruptive history figure

twin hike map with lava flows

Clip from the DOGAMI recreation map that I edited to show the most recent South Sister Flows from 2,200 to 2,000 years ago: the “Devil’s Chain” flows are in purple while Rock Mesa is outlined in Green. There are so many “Devil’s Whatcha-ma-callit” features in Oregon, some cartographers must have had a flair for the dramatic.

While South Sister hasn’t erupted in two thousand years and the Middle and North Sisters have been dormant even longer, the USGS isn’t ruling out future eruptions.

“The Three Sisters region has hosted volcanic eruptions for hundreds of thousands of years, and future eruptions are a certainty. Two types of volcanoes exist in the region and each poses different hazards. South and Middle Sister are recurrently active over thousands to tens of thousands of years and may either erupt explosively or produce substantial lava domes that could collapse into pyroclastic flows. They could also produce lava flows. In contrast, less explosive eruptions could occur almost anywhere in the surrounding area, and construct small cinder cones to large shield volcanoes made mostly of basalt to andesite lava flows. These volcanoes are typically short-lived (months to centuries) and usually don’t erupt again”

If it’s any reassurance, geologists’ ideas of “a certainty” consider a geologic-scaled timeline up to thousands of years…. so life near the Sisters could well be mercifully boring during our lifetimes.

The hiking here, however, is anything but!




USGS Volcanic hazards page for South Sister:

USGS VHP page for all Three Sisters:

DOGAMI flier for Three Sisters:

In the Playground of Giants Green Lake Field Guide

Photo Credit:


(Marmot) By Diliff – Own work, CC BY-SA 3.0,

Many thanks to Heather van Stolk!!




Smith Rock Hike: Volcanic rocks, volcanic heat

Although we’ve lived in different time zones for a while now, my sister Heather and I have been lucky enough to be able to go camping and hiking together once a year… and we kept up the tradition when she visited me in Oregon!

We set our sights on some classic Oregon landmarks that I hadn’t visited yet either: Smith Rock, South Sister, and Crater Lake.

twin trip locations

Map background from

Fun sights between Corvallis and Bend… Mt. Washington and a very festive Sinclair dino in Sisters.

While this was technically a camping trip we copped out and stayed in a hostel in Bend for the first night – Bunk & Brew – which made up for its scarcity of showers by offering complementary local craft beer. This splurge was totally justifiable because it enabled us to get up at the crack of dawn to beat the crowds to some crazy geology.

26.5 million years ago a massive volcano blew its top in central Oregon, spewing enough ash to enough to cover the state of Texas in a layer about 2 meters thick. The Crooked River Caldera eruption would have been catastrophic for any living thing in the area… just check out the phenomenal remains in the nearby John Day Fossil beds. However it was a boon for modern climbers, because it created the foundation of Smith Rock State Park!John Day Formation

The figure above shows the extent of the Crooked River Caldera (red shape #1) and the two other small eruptions that created the John Day formation, including the Smith Rock Tuff. However the rest of the region’s tuff deposits form low hills, not huge towers – why is Smith Rock so different? It turns out that location is key. Because the park lies within the original caldera, shortly after the tuff was deposited super-heated water carrying dissolved minerals rose up through it. This cemented the tuff much like dilute glue would stiffen sand, combining the best of both worlds for climbing – the funky irregular texture of tuff and the hardness of a sandstone.


(sign in visitor center)

As the ash from that explosion solidified under its own heat and weight it created a rock type known as “tuff”. While that determines its composition, the park’s tuff owes its shape to a very different eruption that started 600,000 years ago – the Newberry caldera fifty miles to the south. It spewed out enough basalt to cover an area the size of Rhode Island. This basalt reaches all the the to the southern margin of Smith Rock State Park, and since basalt is tougher than tuff (ha!) it trapped the Crooked River, forcing it to erode in one place instead of shifting around as rivers prefer. This constrained erosion created the steep pinnacles that make rock climbers starry-eyed.

The photos below show the two sides of the river – steep basalt cliffs on the left, softer tuff on the right.


Someday I’ll get out here with my climbing gear, this summer just wasn’t the chance. Heather and I instead hiked the Misery Ridge trail along the river and up steep switchbacks over the spine of the park. Following very good advice from my friend Kate we decided to do the loop clockwise in order to ascend by the less steep trail and descend on the stairs.

smith rock hike map

map from – we did the loop clockwise

The park is littered with strange hollow rocks, like little fairytale huts for the four-legged park residents. Some are large enough to fit humans!


Heather enjoying the shade

These fantastic shapes were formed by pressurized bubbles in molten but rapidly cooling tuff, and have slowly eroded out of the cliffs. There was a whole village of them near the junction of the River and Misery Ridge Trail.



Looking up at Monkey Face from the River trail. Heather christened my head wear “the typical dorky geologist hat”. I have no shame.


Heather couldn’t resist climbing some more rocks before descending the stairs

Temperatures were predicted to get up to 97 degrees that day so we started at 8:30 AM. After a leisurely stroll along the river and a significantly less leisurely struggle up the ridge we reached the top at 11 AM for a celebratory round of gummy candy overlooking the famous Monkey Face formation.

Scores of people were ascending the stairs at noon as we were passing them going downhill. Several people were prostrate on the side of the trail trying to cool down, and most were markedly miserable.  Smith Rock is a popular park on good roads close to civilization (Bend) and the trail is only 4 miles. This might lure visitors into a sense of complacency but it’s not by any means an easy hike. The signs at the trail heads recommended sturdy boots and drinking a liter of water every two hours while hiking – evidently it’s not exaggeration. I guess the trail is called Misery Ridge for a reason.


I may never climb the 5.14 (insanely difficult) route up Monkey Face, but at least I climbed its mini-me on the playground!


After eating lunch and saying goodbye to Smith rock we stopped by an auto shop to address Jo the Adventure Civic’s warning light (she’s never a fan of the climb over the Cascade passes), and then made our way to the beautiful Elk Lake USFS campsite 45 minutes southwest of Bend. We had a much longer hike planned for the next day, so we settled in for some serious relaxation at the lake shore…


Life is tough 😛


Heather’s wonderful photos!





Accreted terranes: a slow-motion pileup on the Pacific Coast

Oregon became a US State in 1859, so you would think the underlying rock would at least be North American. It turns out that like the modern population of the state, though, southwest Oregon’s bedrock is an international melting pot.

Let’s take a step back and deconstruct that piece of jargon I threw out there in the post title.

Accreted = added on, and terrane = small bit of independent continent.

If you’re familiar with the theory of plate tectonics, it’s often simplified into a huge shifted puzzle of large plates that either collide violently or slide under each other neatly. However there are actually some smaller pieces that get swept up in the cycle of creation and subduction. These could be pieces of oceanic crust that got scraped off of a subducting plate or a volcanic arc like Japan, for instance.

When the supercontinent Pangaea was torn apart by rifts starting around 200 million years ago it started a planet-wide game of bumper cars. The Mid-Atlantic rift separated North America from Europe and it pushed North America westward; this sped up activity along the subduction zones on the continent’s western coast. The Oregon coast shows evidence of the odds and ends of lithosphere that the newly liberated North America plowed into on its journey west.


Figure showing how accretion works, from Miller 2014

The southwest coast of Oregon where my family vacationed is a giant 11-car pileup of accreted terranes ranging in age from 180 million to 100 million years old. When we hiked on Cape Sebastian we were standing on the Gold Beach Terrane, which took an unconventional path to Oregon. Unlike the neighboring terranes that were scraped onto the continent by converged plates from similar latitudes, studies of the rocks found in the Gold Beach Terrane show that they originated near southern California and were transported north on a transform fault similar to the San Andreas!


Closeup of southern Oregon and northern California from Miller 2014 showing the sequence of terranes plastered onto the coast

The most prevalent family of rocks in the Gold Beach terrane is the Otter Point Formation. This melange formation (melange being geology-ese for “ungodly mess of rock types”) contains mostly sandstone with dashes of conglomerate, mudstone, bits of interleafed sandstone and shale, and blocks of misplaced metamorphosed oceanic rock. The sandstone from this formation creates many of the dramatic sea stacks that we saw at Secret Beach, Arch Rock, and near Port Orford.


Arches, mussels, and starfish on the Otter Point Sandstone at Secret Beach

On Myers beach we saw another Otter Point rock that, although softer than the sea stack sandstone, still had a great story to tell.


Turbidite on Myers Beach

These rocks are called turbidite, and were originally deposited in a deep, quiet environment underwater on the continental shelf. The water was so calm at that depth that any storm deposits that rushed out of a delta upslope sorted themselves gently into larger, heavier particles on the bottom and lighter particles on top. Eventually they formed parallel layers of sorted sediment, one per storm event, and were cemented together by pressure and mineralization.

And then their quiet neatness was ruined when the rocks were scraped onto another continent a few million years later.

Now that turbidite has been bent at 90 degree angles, faulted, hoisted above sea level, and is eroding into nice fine beach sand. Not the retirement it was hoping for, I think.


Miller, Marli B. Roadside Geology of Oregon. 2nd ed., Mountain Press Publishing Company, 2014.



Forget rising tides, what about a rising coast? Uplift at Cape Arago

So in my last post I showed off some pretty pictures from Shore Acres State Park… that raise questions.

What’s with the rock blobs?


Why are the cliffs tilted?


And further south, why are all the sea stacks about the same height, and the same height as the mainland?


Unfortunately those blobs are not about to hatch some rock-type Pokemon. They have something much less exotic at their center – small irregularities like pebbles or shell fragments. As groundwater slowly flowed though the sandstone it preferentially deposited minerals on larger particles, creating a snowball effect around imperfections in the otherwise relatively homogeneous rock. This extra “cement” makes those areas harder and more resistant to erosion than the surrounding rock.

The tilting rocks are a reminder of the pressure that the coastline has been under over the millennia – it’s the western edge of north-south trending downward fold, or syncline, that includes all of Cape Arago.

miller 2014 cape arago adjusted

Pressure from the colliding Juan de Fuca and North American plates farther offshore has made the coast buckle and rise over the millennia. Over time the waves wear a flat platform in the rocks, only to have that platform eventually raised out of their reach. There are five different such platforms visible in the Cape Arago area which have been uplifted at a rate of about 3 feet per thousand years.

The lowest visible terrace in the area, called the Whiskey Run Terrace (Q1 in the diagram above), rose from the sea about 80,00 years ago. Although its top might have been elevated above the waves they continued to erode its sides, eventually breaking much of it down into individual sea stacks. Similar terraces and the same wave action occur all along the Oregon coast, creating families of sea stacks with matching elevations.

The uplift isn’t a completely steady process – when the North American plate jolts forward and releases the tension with the subjecting Juan de Fuca plate the coast can plummet a few feet in elevation. However based on the syncline and pattern of older terraces at higher elevations, it seems like upward motion has won the long game.

Image result for oregon coast elevation cascadia quake

Image from Leonard et al. 2004, showing subsidence after quake

I missed an amazing photo op at Sunset Cove near Shore Acres State Park. Apparently at low tide you can see the stumps of trees that were submerged during the Cascadia mega-quake in 1700. I’ll just have to visit again to meet them in person…. not a hardship at all!


Miller, Marli B. Roadside Geology of Oregon. 2nd ed., Mountain Press Publishing Company, 2014.

Lucinda J. Leonard, Roy D. Hyndman, Stephane Mazzotti; Coseismic subsidence in the 1700 great Cascadia earthquake: Coastal estimates versus elastic dislocation models. GSA Bulletin ; 116 (5-6): 655–670. doi: