Tag: Geology

Hike with a Geologist at Barnes Butte

View up to Barnes Butte from the trail

At first glance, a visit to Barnes Butte in Prineville looks a lot like much of central Oregon—a landscape of sage brush, juniper, and volcanic rimrock. It is difficult to imagine that Barnes Butte is, in fact, the inside edge of a massive supervolcano that—though now extinct—erupted more than 240 cubic miles of material forming a caldera roughly 29.5 million years ago.

Approximately 25 miles by 17 miles in size, the oblong-shaped Crooked River Caldera reaches from Smith Rock State Park in Terrebonne east to the Ochoco Reservoir and south to the Prineville Reservoir and Powell Buttes. For something so large, it might seem surprising that it wasn’t until 2005 that a couple of scientists first noticed its presence.

However, standing in the parking lot of Barnes Butte City Park with Carrie Gordon, a retired geologist, and willing hiking partner, it became obvious why such a large geological structure went unnoticed for so long. Seriously, what volcano?

The Hike

  • Trailhead: Barnes Butte Trailhead
  • Distance: Varies. (2.7 miles w/565 feet elevation to top)
  • Details: Large parking area; no pass required; No restrooms (port-a-potty may be available)  

Introductions

It was a warm early fall day when I met Carrie in the parking lot of Barnes Butte City Park. Wildfire smoke created a haze across the skyline, but you could still just make out most of its features, including the Cascade Volcanoes in the distance.

Carrie, a small energetic woman, was all smiles as we gathered at her vehicle for introductions.

“I worked 40 years for the Forest Service,” Carrie said, “As a forest geologist.”

She explained that her job mainly entailed keeping track of material sources, like gravel.

“It is one of those careers that are just a hoot and a half,” she exclaimed.

Yes, this is Carrie. And we were just getting started.

Tall Tales

I asked Carrie to tell me about where we were standing.  After all, I couldn’t see any so-called “volcano.” She quickly pulled out her geology maps from her vehicle to orient me to the space and began to weave the tale.

“Jason McClaughry and Mark Ferns from DOGAMI started mapping in 2005,” she said. Originally, “they were supposed to map a 7.5-minute quadrangle,” Carrie continued.

Plans quickly changed, however. McClaughry and Ferns were tasked with finding water resources for Prineville, but while mapping, certain geological features started reshaping their goals.  By the end of the project, they had mapped over 903m2—and reshaped our understanding of central Oregon geology.   

“The cool thing about geology,” Carrie began, “The rocks don’t change but the story changes. We add to our body of knowledge, and we can go, ‘oh okay’…”

Anatomy of a Calderas

Perhaps the most important change to the story that McClaughry and Ferns brought to light was the chapter on the Crooked River Caldera. 

“Calderas are a little sneaky,” said Carrie.

Unlike, the very conspicuous Cascade peaks, “seeing” a caldera requires reading the landscape very differently. They are not peaks, rather, Calderas are mostly depressions.

Carrie explained: “Basic caldera formation is you have magma that is coming up to the Earth’s surface to the point you get a collapse.”

In the case of the Crooked River Caldera, these eruptions took place from about 29.7 to 27.5 million years ago. These were massive eruptions of rhyolitic lava, including volcanic tuff, that created a void below the volcano that eventually collapsed creating a 26 by 17-mile depression.

In addition, a ring fracture develops during caldera formation—allowing rhyolitic lava to intrude and bulge up along the side of the collapse.

Evidence of the ring fracture of the Crooked River Caldera can be seen at places like the Prineville Reservoir and Peter Ogden Wayside, where older rock that pre-dates the eruptions is tipping toward the interior of the caldera.

In addition, and perhaps even more obvious, rhyolitic domes can be observed marking the Crooked River Caldera Boundary. Carrie pointed to each—Powell Butte, Gray Butte, Grizzly Mountain, and, of course, Barnes Butte.

“This is the evidence that they [McClaughry and Ferns] found,” Carrie stated.

Looking out toward Gray Butte and Grizzly Peak (photo credit: Carrie Gordon)

Tuffs

I was beginning to see it—with many of the peaks visible from the parking lot—the caldera was taking form when Carrie whipped out another visual aid.

“I brought my box of rocks too,” she proclaimed.

Carrie pulled out two rocks with large flecks of material embedded within them—tuffs, I would soon find out.

“The cool thing about tuffs is they tell you about volcanic activity,” said Carrie. Tuffs are commonly associated with large violent eruptions as you see in caldera-forming.

“Tuffs are formed from bits and pieces of pumice and bits of rocks as it comes up through, in our case accreted terranes,” during an eruption, said Carrie.  “It is a mishmash of stuff.”

Pulverized stuff mostly, like ash, but also some solid flecks of rock, like pale gray pumice, embedded in the matrix—that is tuff. 

“It sparkles at you due to the crystal fraction in the ash,” described Carrie holding up two samples, her eyes sparkling more than the rocks.

Tuffs are also lighter than other forms of igneous rock, like other forms of rhyolite and basalt, as they are full of air pockets. She handed me one of the tuffs to weigh in my hand and basalt in the other—yep, I could feel the difference.

If you ever visited Smith Rock State Park, you have seen tuff. It is the tuffs that people mostly climb on. 

“Easy to pound in your pins,” Carrie remarked.

Tuffs from the Crooked River Caldera

Geochemistry and Cooling

Carrie had other rock samples in her box. She pulled out a shiny, black rock called obsidian, and a striped rock called banded rhyolite.

“These are all rhyolite geochemistry,” said Carrie. “Rhyolite has higher silica content than basalt and it tends to be blocky when it chills.”

However, the similarities end there.

“The thing about rhyolite is it comes in so many different forms.”

Tuff is the result of violent eruptions that pulverize rock, while obsidian and banded rhyolite are both formed as lava flows.

Obsidian is glassy because it cooled quickly enough that crystals were unable to form. Banded rhyolite, on the other hand, forms crystals that capture the layering that often occurs as lava flows.

“This is what makes up Grizzly and Gray Butte…” Carrie added, holding up the banded rhyolite.

She continued, holding up the two tuffs she had pulled out originally.

Tuffs to the left and obsidian to the right

“These are the same rock,” she explained. Only one had undergone a form of hydrothermal alteration, turning it “pistachio green,” while the other more “beigy” rock had not.

“And that is tuff,” Carrie concluded, putting her rocks back in her box.

She also mentioned granite—another form of rhyolite formed by a slow cooling process under the Earth’s surface.

“It is the same composition as obsidian,” Carrie reiterated, but “buried a long time.”

Just one more reminder to not take your rhyolite for “granite” (pun intended).

More samples from Carrie’s box of rocks

Off to the Races

At this point, we had been chatting for about 20 minutes and decided it was about time to hit the trail. The trail system at Barnes Butte City Park is rather extensive, but we kept it simple and headed up the Jockey Trail that goes along the base of Barnes Butte—an old trail that the landowners used to run horses on. 

As we started off on the rocky, dusty path, Carrie told me about the other trails that run through the park.

Apparently, much of the land was an old ranch. In addition to hiking the old horse track, there are also a lot of old cattle trails that are now hiking/biking trails that run through old grazing fields and around what used to be an irrigation pond.

Before that, there was even mercury mined on the Butte for a short time.

“See the main draw,” she said looking up toward the butte, “ there is an old BLM road that goes up to where the mercury mines in the 1940s are…. [The mercury mine is] courtesy of the caldera and volcanism.”

Mercury, lead, and gold, as well as Oregon’s state rock, the thunder eggs, rely on silica-rich waters to concentrate and form these minerals.

“You can take a footpath to the top of the butte,” Carrie added, “there are a lot of options.”

Rivers in the Sky

Soon we arrived at an embankment, apparently part of the old irrigation pond, when Carrie unexpectedly began hiking off the trail up the hill.

“What are you seeing?” she asked me, as I followed her onto the side of the embankment.

“Looks like some kind of layer of fine sandy stuff…” I responded hesitantly, “Oh, and the rocks are rounded.”

“You got it!” she proclaimed with a smile. “So, what we are seeing is lakebed and riverbed sands and cobble.”

Then turning, she pointed out to a suite of rimrock, lava plateaus.

“If you look across at our plateaus,” she explained, “you are looking at the old valley floors!”

She explained that each lava plateau was the result of an individual basalt eruption event (part of the Deschutes formation) that filled the valley at that point in time—the oldest being 7 million years old and the youngest only 3 million years.

Over time, the land area surrounding the lava-filled river channels eroded. As a result, what were once lowlands and river channels, are now basalt plateaus.

“This is inverted topography,” said Carrie—what was low is now high.

“What we are looking at here is the infill,” said Carrie looking back to the sand and cobbles, “the eroded remains of a valley bottom.”

Looking out at the lava plateaus

Perspectives

Carrie and I continue wrapping up and around the hill of infill where we could get a better view of the young lava flows and the much older rhyolite buttes of the Crooked River Caldera.

As we hiked, we passed by some bright yellow rabbitbrush still in bloom. Carrie told me how she uses it to make cloth dye; and we briefly got on a tangent regarding natural dyes—a side passion of Carrie’s.

“Rabbitbrush makes the best dye!” she proclaimed.

Speaking of color, Carrie pointed out a pale green patch of ground in the distance—to the left of Barnes Butte from where we stood.

She told me how she used to drive by and wondered at the green color—“it just stayed pistachio green” all year long. Eventually, she realized it was tuff.

Though the rock that makes up Barnes butte is a solid rhyolite dome, tuffs can be observed around Barnes Butte as a few outcroppings, and as what geologists call “float”—rocks that have moved from their place of origin.

Carrie pointed out a few outcroppings of Barnes Butte tuff that lay just in front of us—“the high points,” she noted. 

A Step Back

Carrie also addressed the hills that lay on the far horizon, outside the Caldera’s boundary.

“Most of what we are looking at on the far horizon are Clarno andesites,”  said Carrie looking east—volcanic rocks from a period preceding the Crooked River Caldera eruptions.

Of course, mixed up in all of it, is even older rocks. Accreted terranes—jumbles of earth materials that become permanently attached to a land mass of a completely different origin—make up the basement rocks of Oregon.

Carrie told me about how older maps used to show a pocket of limestone in the area. It was “weird” at first, but as Oregon’s geological story unfolded it became apparent that the limestone was from an accreted terrane. The limestone would have come from some distant shallow sea before it was added to the continent 100 to 400 million years ago by the forces of plate tectonics.

Only later it became part of the Crooked River Caldera. The past, literally, resurfacing by way of the Caldera’s eruption.

Flash Forward to Newberry

Carrie turned to face the interior of the Caldera again. There was still one more point in time to discuss.

In addition to the lava flows that make up many of the plateaus around Prineville, an even younger period of volcanic eruptions graced the Caldera in geologically recent times—the Newberry Volcanics.

Newberry has been erupting for the last 400,000 years and remains active today. Its most recent eruption was 1,300 years ago.

“Darn it all!” she exclaimed. “I was hoping it would be clearer…It [Newberry] is a big shield volcano,” said Carrie, “It barely shows over the horizon.”

Interestingly, some of Newberry’s flows reached into the Crooked River Caldera.

Carrie described one of these flows:

“That basalt flow was going down the ancestral Deschutes River, near O’Neil Junction, where it dropped into the Crooked River drainage, headed to Smith Rock. Here it smacked into Smith Rock pushing the Crooked River over to its present course.”

Those who have visited Smith Rock State Park and hiked any of its trails know this basalt flow as the calf-burning, heart-pumping climb out of the Crooked River Canyon, and back to the parking lot.

Next time you visit, “Look at what is at the bottom of the basalt flow…” advised Carrie. “There is river cobble there.”

Whether it is the Newberry basalt flow, or any one of the other flows that passed through, each time the Crooked River is displaced.

“It was doing its level best to be a valley bottom and these stupid basalt flows come in,” Carrie described in her own colorful way. “The river is like ‘okay, I will find another route’.”

Ashes to Ashes

At this point, Carrie and I resumed our walk along the old racetrack and took a left, wrapping around to the other side of the embankment facing Barnes Butte. Song birds flitted by as we walked. 

“One of the best-kept secrets,” Carrie shared, “we have a nesting osprey pair here.”

As we meandered around the bend, Carrie pointed out what looked like really fine sand.

“This is volcanic ash,” she explained. “When Mazama erupted, we got a foot and a half of fine ash.”

Mount Mazama—a massive stratovolcano blew it’s top 7,700 years ago, forming a smaller caldera that has since filled with water forming Crater Lake.

Carrie continued: “One of the things that happened is the winds will blow ash and it will catch on the leeward side of the hill,” she explained.

Carrie then proceeded to scoop up a handful of the ash and show how me how to look at it with a hand lens—white pumice fragments and black hornblende or magnetite could be made out among the grains. Of course, her favorite part, and mine too, was to look at the ash in the sunlight. 

“The best thing about volcanic ash is it winks at you,” said Carrie. “It is the reflection of the crystal fragment of volcanic ash.”

You don’t get that same winking with sand, explained Carrie. Only ash has the ability to sparkle.

Volcanic ash capable of winking in the sun

Blowing in the Wind

The ash is also important to the soil of the area. Loess—windblown sediment—is rich in many minerals and provides the starting material from which soil forms.

Of course, loess is not the only input into the area.

“Don’t forget we are in this pocket here,” reminded Carrie, “We had all the river systems and lake deposits that are actual sand and gravel.”

Alluvium—water-transported sediment—also contributes to soil formation, even in places you might not expect. Powell Butte, for example, is mostly covered with river sand.

“Something [i.e., a river] was moving across there at one time,” said Carrie.

Now, these old river channels are a ready source of water for the City of Prineville. When the City looked for places to tap for wells, surprisingly the best places were on the bottoms of the lava flows that once were river channels.

“This was the thing that blew me away,” Carrie smiled. 

Barnes Butte

Carrie and I reached another junction and took the trail heading up Barnes Butte. As we climbed, we passed by several large hunks of reddish-brown rock. Unlike the rocks down below, these were not round, but jagged.

“All the hunks of rock are rhyolite,” said Carrie.

I asked Carrie how she knew it was rhyolite, aside from knowing where we are at. Carrie picked up a piece of the rock and knocked it against another.

“It sounds glassy,” she explained. “Part is how it sounds, and if you can heft it.”

According to Carrie, compared to basalt, another prolific volcanic rock, rhyolite is not as heavy. So if you find a gray rock that is relatively lighter and glassier, it could be rhyolite.

Juniper

As we continued up the rocky hill Carrie, I noticed a juniper with its roots clinging to a juniper tree.

Off-hand I asked Carrie, “Do junipers like rhyolite?”

Surprisingly, she answered in the affirmative.

“That’s a cool story!” Carrie proclaimed. “Western Juniper has become invasive.”

Though western juniper is a species native to central Oregon, it has been creeping into areas that it normally wouldn’t. Fire exclusion, grazing pressure, and climate variability have all been cited as reasons for the spread of the waster juniper.

“And it uses a lot of water,” Carrie added, a highly valued resource in the area.

“This is all rangeland,” Carrie explained, it should have “more grasses and sagebrush component.”

In short, western juniper shouldn’t be so prevalent.

Instead, according to Carrie, western juniper is a first colonizer. Its range historically was limited to rocky areas—like our rock-grasping juniper.

“This is a rhyolite knob,” concluded Carrie, “and this is a very well-behaved juniper.”

Well-behaved journal growing from rhyolite rocks

Lichen

We continued up the Barnes Butte for a stretch but then decided to turn around. I was curious about finding tuff, so Carrie suggested we check the lower trail.

As we walked, I started noticing all the lichen and moss growing on the rhyolite and asked Carrie about it.

“Are they picky?” I asked, wondering if only certain lichen grow on certain kinds of rock.

Carrie didn’t think so, but instead mentioned how they might be used to age-date rocks.

Estimates of the age of a rock can be estimated based on the growth and size of the lichen that grows on it.

“Has the rock been sitting in place?” Carrie asked rhetorically. “Then you can get some age dates.”

Additionally, some plants do seem to prefer certain rock types. During the mapping of Mill Creek—an area adjacent to the Crooked River Caldera—McClaughry and Ferns found that, following a fire, much of the rhyolitic rocks were being colonized with manzanita. Manzanita soon became an indicator of rhyolite geology during the mapping.

Lichen growing on rhyolite

Recommendations

As we continued downhill, Carrie spotted some of the green tuff as float (loose rock) along the pathway—more evidence that we were, in fact, in a Caldera.

As we walked, Carrie offered me a lot of recommendations—video recommendations, places to visit, and hikes to take. She had a real knack for suggesting hikes I hadn’t been on.

But perhaps the strongest suggestion she has was to check out some of the Crooked River Caldera sites.

One of these places was Pilot Butte. (Yep, I hadn’t hiked it yet.)

You can see the Cascade Volcanoes from Pilot Butte—” a lovely white line of volcanoes,” as Carrie put it, but she wanted to make sure I didn’t miss the main event. 

“It [the Crooked River Caldera] is one huge volcano compared to the pretty pristine cones,” she added.

Other places she recommended for observing attributes of the Caldera include the Prineville Reservoir, Peter Skene Ogden State Park, Ochoco Reservoir, and, of course, Smith Rock.

I recommend hiking with Carrie. She is a hoot-and-a-half.

Carrie Gordon is a retired forest geologist. She was the Forest Geologist on the Ochoco National Forest and Crooked River National Grassland, U.S. Forest Service, headquartered in Prineville, OR. She retired in 2017. Carrie is also an active member of the Central Oregon Geoscience Society and an Oregon Master Naturalist through the OSU extension program. Carrie has had a life-long fascination with the land and the rocks, listening to the stories they tell.

Hike with a Geologist at Seal Rock

About 15 million years ago basaltic lava released from fissures in northeast Oregon and southwest Washington poured through the Columbia River basin, traveling across the Pacific Northwest. Collectively these flows are known as the Columbia River Basalts.

What is perhaps most intriguing is just how far some Columbia River Basalts traveled. Flows can be found in locations as far afield as Silver Falls State Park, for example. Other flows traveled hundreds of miles from their origin through the Coast Range mountains to the Pacific Ocean.

Seal Rock State Park is the site of one such flow—making it a premier location for geology enthusiasts.

So, when I reached out to Sheila Alfsen from the Geological Society of Oregon Country for a hike and interview and she suggested we visit Seal Rock, it was met with a resounding “yes! “

Circuitous routes

I met Sheila in Philomath so we could drive to the coast together and talk geology along the way. As we headed out, she told me a bit about her background.

Sheila’s path to geology was a circuitous one.

She started out as a volunteer and teacher’s assistant at her own children’s schools where she realized she had an interest in and a knack for teaching.

Then, when state requirements insisted she go back to school for her job, her mind and life path were changed.

“My first class was oceanography,” Sheila gushed, “and the first thing we talked about was plate tectonics…This was everything I wanted to know. I was hooked on geology after that.”

Soon enough, Sheila had earned an associate degree, and later a Bachelor’s in Geology and Spanish, and a Master of Arts in Teaching (MAT).

She started teaching high school science and eventually moved on to teaching college courses, some with her mentor, Bill (William) Orr. 

Sheila found her passion—teaching geology.

“In Geology, you aren’t just talking about the rocks, but what they tell us about the history, and therefore, future of the planet. In Earth Science, you also talk about the oceans and atmosphere,” Sheila explained—It is all the Earth Systems. 

“I can teach basic principles of physical science within the context of earth science.”  Everything has a geology connection.

Highway 20

Our first stop on the way to the coast was Ellmaker State Wayside off Highway 20.  Here, Sheila laid out a plan for the day and gave a bit of background on the road we would be following to reach Newport. 

Several decades ago, the State Department of Transportation attempted to reroute the highway. Back then, the highway was routed through Eddyville where it followed the Yaquina River on windy roads that not only made the drive to the coast longer but more hazardous.

So, the State hired a construction company to cut a new route through the coast range. But problems ensued. The land was unstable, and landslides became a  huge issue.

“Basically, they didn’t consider or understand the geology until they already had a lot of problems,” Sheila explained.

Their oversight came at a high cost. By that time, the first company hired had gone broke and a new construction company was brought in with more geological expertise.

“It took 10 years later and over double the budget to get it done,” said Sheila.

Ellmaker State Wayside off of Highway 20

Structure

Sheila and I hit the road again to see just what exactly had thwarted the project. Turns out you can see the problem in the rocks.

As we drove up the highway, Sheila pointed out roadcuts, as we passed. The rocks in the roadcuts were light colored and dipped to the east as we headed up the pass.  Later, a bit further up the road, the layers were arranged nearly horizontally. Then, we reached a spot where the rock layers had turned—dipping westward toward the ocean.

Here we pulled over to take a closer look. 

Sheila explained that the reason that the highway road project didn’t succeed is that from the start they didn’t pay attention to the geology—specifically, the structure of the rocks.

“When we say structure in geology,” Sheila explained, “we are talking about how the rocks are folded and how they are positioned.” 

She went on “Geological structure is how the rocks are put together. It makes a big difference.”

The structure we were observing as we came over the Coast Range on highway 20 is what is called an anticline.

“An anticline is an arch,” said Sheila “and this is one limb of the anticline,” she pointed westward, “and the other way is the other arm.”

Sheila went on to explain that this giant arch was also plunging—dipping to the north.

“Pressure from this direction,” she pointed west again, “from the Juan de Fuca plate, creates the anticline.”

The Juan de Fuca plate is the current tectonic plate that is subducting (going under) the North American Plate just off Oregon’s coast. However, according to Sheila, there is also pressure from the Klamath Mountains to the south that has resulted in a “rotation of the whole coast range”—this is what makes the anticline tilt to the North. This is why pieces of rock were breaking off and sliding onto the road, inhibiting the progress of the construction.

Sheila demonstrates the shape of an anticline.

 Tyee Formation

We got out of the car to get a closer look at the rock layers themselves.

As we stood there talking, a police car pulled up to see if we were okay.

Sheila laughed, “Just a little geology lesson,” she told them, before inviting them to join us. They declined, but I got the sense that this was not the first time Sheila has made such an invite.

“This rock is the Tyee Formation,” Sheila described as we looked across the highway at the tilted layers.“This layer of rock is famous,” she went on, “It goes all the way down to the Klamath Mountains.”

The Tyee Formation is comprised of sandstone and shale, formed from sediment that was deposited in a large underwater delta some 45 million years ago.  There was no Willamette Valley or Coast Range at the time, just a gigantic bay. The Klamath Mountains were already in existence and shedding sediments into the bay to form the delta.

“The delta was huge and went all the way out northward to about Dallas,” described Sheila. I tried to imagine Oregon 45 million years ago, missing a good quarter of its landmass.

Eventually, the delta turned to rock and was folded and lifted into the Coast Range, powered by the subduction of the Juna de Fuca plate—a process that continues even today.

Turbidity Currents

 Sheila suggested we walk closer to the roadcut to look at the rocks of the Tyee more closely.

She explained that when the sediments from the Klamath Mountains would fall into the bay, this resulted in “turbidity currents”— a sudden flush of sediment and water rushing off the continental shelf before settling into distinct layers.

These fast flushes of sediment became the layers of rock that make up the shale and sandstone of the Tyee formation. The sandstone layers in the rock formed from quickly settling sand, and turned into thick, light brown colored layers of sandstone.  Clay, on the other hand, “takes a long time to settle out.” These clay layers presented themselves as dark gray, incised bands in the roadcut.

“One layer of sand and one layer of clay above it is one event,” Sheila pointed out. “This is what the Coast Range is made of.”

Sheila pointed out the shiny flecks that glittered in the sandstone layers. “Muscovite,” she called them, “from the Idaho batholiths”—a clue that when the Klamath Mountains were first accreted, they were near the Idaho border.

The Tyee formation up close.

A Closer Look

Sheila soon began to poke around, digging into the roadcut rocks.

“If we are lucky,” said Sheila, as she pulled a rock from the base of the loose shale layer, “we will find little trails of marine organisms.”

You see, between each turbidity current, the organisms that are living and feeding on the sediment before they are wiped out by the thick sequence of sand that suddenly gets dumped on them. Their fossil remains can often be observed as trails in the sandstone and can be used to date the layers.

Sheila and I continued to pick at the roadcut and examine any loose pieces of rock that came away easily. The shale broke off in thin layers, while the sandstone felt gritty and rough.

I held a piece of rock up to my eye with a hand lens to see the shiny flat muscovite mineral amongst the grains of tan-colored quartz and feldspars.

“A geologist sees things. When you learn about the geology you look at the world differently and it is beautiful.”

Tyee sandstone with fossil trails of marine organisms.

The Road to Jump-off Joe

Sheila and I hit the road again. We were going to make one more stop before heading to Seal Rock—a place called Jump-off-Joe.

After another 30 minutes of driving through the Coast Range, we reached Newport and the Pacific Ocean.  We drove North a bit on Highway 101 before veering off onto a side street and pulling over in front of a roadblock and a parking lot with an oceanfront view.

Just past the cliff edge, you could see an old building foundation in disrepair, as the land around it had subsided and begun the process of crumbling into the sea.

As we stepped out of our cars for a closer look, Sheila laughed at a sign on the adjacent hotel that boasted about its “ocean views.”

“This building was a football field away from the edge,” said Sheila, thinking back to her last visit. “The view is getting more and more exciting,” she snickered.

“Coastlines are unstable,” said Sheila. A lot of the rock on the coast is layered sedimentary rock and “some are inherently unstable.”

The fact that someone tried to build in this location was ludicrous to Sheila.

“Immediately it started slipping,” said Sheila. “Yaquina Head in the north, to the opening of the estuary is all landslide area.”

Time and the elements had really taken a toll on the abandoned structure. Graffiti covered large portions of the dilapidated foundation. Signs warned people to stay back.   

It was all a bit ominous. We kept our distance from the edge.

Derelict abandoned building at Jump-off Joe

Sandstone Arch

Then, Sheila pointed to the right of the crumbling foundation, a small sandstone mound stood just below on the beach. Another sign of erodibility and instability of the rocks that make up much of this part of the coast.

“Back in the late 1800s or 1920s that was an arch,” said Sheila pointing to the small, but visible sea stack. “It has been eroded.”

The location of the arch was once referred to as “Jump-off Joe,” apparently because the cliff down to it was steep. It was quite the site to see back in the day, as evidenced by a quick google search.

Now, it was hardly an attraction, having been weathered down to a remnant of its former self.

Of course, not all the rocks on the coast are as suspectable to erosion and weathering as much of Newport Bay. Yaquina head, for example, just visible to the north is made of basalt—a much more resistant rock.

“That is why those are points out there,” reasoned Sheila. In fact, basalt rocks make up much of the Oregon Coasts’ headlands.

But where did all this basalt come from?

I was about to find out.

View of the remnants of Jump-off Joe

Sea Stacks

Sheila and I took off again for our final destination—Seal Rock State Recreation Site.

We arrived around lunchtime and stopped for a quick picnic lunch at a table just behind the bathrooms.

After lunch, we followed the paved trail back up through the twisted shore pines that led out to the Seal Rock viewpoint. From here, sea stacks of various sizes jet out of the ocean in a curved line.

“We call this a ringed dike because it forms a ring shape,” said Sheila. “What used to be a low space fill with lava, and the stuff around it erodes away,” she explained.

Elephant Rock

The largest of the rocks—a massive rock towering structure—is known as elephant rock.

“Elephant rock is what we call a sill,” said Sheila, “in igneous geology, a layer of lava that squeezes between two layers of rock.”

“In this case, the lava didn’t intrude between the layers, it just fell into the soft sediments of the coast and re-erupted,” Sheila backtracked,  So, “not technically an igneous sill…but it is basalt.”

Basalt—a hard and resistant rock. Waves “eat away at sandstone,” but basalt, not so easily. 

“You can see the cave under the rock, to the right,” said Sheila as we started further down the trail that leads to the beach. “It is sandstone. It is easier to eat away.”  A small cave carved into sandstone cliffs to our right.

Just like at Jump-off Joe there are signs that warn people not to walk on these cliffs. Just like Jump-off Joe, the area is unstable.

Sandstone to the right with basalt to the left in the distance at Seal Rock State Park

Cobbles

The trail eventually petered out as we neared the beach. We carefully clambered over rounded rock cobbles that had been turned by the waves.

“This is nicely polished basalt,” said Sheila as she picked her way down.

Basalt, Sheila explained has cracks in it that develop when the lava cools. The columns of elephant rock are a great example.

“It is easy for the waves to break it up,” remarked Sheila.

Basalt cobbles.

Magnetite

After some careful maneuvering, we reached the beach and headed south, following the ocean’s edge where the sand is firm. Soft gray-colored sand lay underfoot, but Sheila was on the hunt for something darker.

“If you look at the beach, have you seen areas with dark sand?” asked Sheila. “That is magnetite.”

Magnetite, she explained comes from weathered basalt.  Magnetite is a dark-colored mineral made of iron and magnesium—making it magnetic. It is heavy and often accumulates in areas.

“Near stream you see it,” Sheila advised.  She had seen a thick layer of it on previous visits to the beach and was curious to see it again.

“Here is magnetite,” said Sheila a few moments later—though not the band of magnetite she was hoping to find.  Black sand lay in a rippled pattern on the otherwise pale-colored sand.

Magnetite on sand.

Dynamic

“Here we are watching the pattern that develops in the sediments,” said Sheila.

She went on to explain how sediments are pushed up on the beach at an angle by the surf and then fall straight back down the beach so that they constantly are moving along the shoreline.

“A coast is a dynamic place, always changing,” she affirmed.

The magnetite pattern was just one sign of constant coastal change.

A Lava Story

Sills, dikes, cobbles, and magnetite… we headed toward the far shore and crossed a small creek. It was time to get to the main event. Where did the lava come from?

“This is the southernmost extent of the Columbia River Basalt,” said Sheila.

The Columbia River Basalt, as mentioned earlier, are lava flows that originated from fissures in eastern Oregon and Washington some 15 million years ago.

“They made their way through the Cascades, down the Willamette Valley, and as far south as Salem Hills,” said Sheila.

In fact, the Salem Hills are Columbia River Basalts—“they are just coved with vegetation,” explained Sheila. 

“A typical flow was 100 ft thick,” Sheila described. “Imagine a wall of lava that is one hundred feet thick and flows like syrup.” 

Remarkably the flow stayed liquid as it traveled all the way to the coast. This is different than one might expect especially if you have seen a Hawaiian eruption. Sheila described seeing a lava flow in Hawaii cool right before her eyes.

In the case of the Columbia River Basalts, there is “so much lava, the outside will crust over, and it will break through its own crust and keep going,” Sheila described. “It could advance 3-4 miles per day.”

According to Sheila, the basalt rocks we were seeing were Wanapum basalt, the youngest of the Columbia River Basalts, specifically the Gingko flow.

Final Contact

By now we had made our way over to the sandstone and basalt cliffs opposite the ocean. Here, we passed by what looked like a small black stone wall jetting out of lighter-colored sandstone.

“It was probably soft sand when the dark lava intruded but now it is sandstone,” explained Sheila.

“This is part of the ring dike,” said Sheila, “a crack that is filled with lava.”

Dark basalt lava intruding on sandstone.

 We saw more cobbles of polished rock before reaching the far end of the ring dike.

“Basalt is here,” said Sheila pointing up at some heavily fractured black rock overhead.  “And the contact between the basalt and the soft sediments,” she pointed to a deeply eroded area below the rocks where thin ribbons of rock layered together.

“Looks as fresh as it did when it cooled 15 million years ago,” she exclaimed with a smile.

The far end of the ring dike.

Tracking Flood Basalts

At this point, Sheila and I turned to retrace our steps. But before we made it back very far, we stopped for a quick geology lesson and big-picture discussion on the basalt flows. 

“Coastal provinces are kind of a collage of everything that has happened inland,” said Sheila, as she traced a sketch of Oregon into the sand.

She began pointing out important landmarks… “the Columbia River, Cape Blanco…”

“Cracks opened over here and issued lava,” she pointed up to the northeastern part of the state. “Most of it came down the Columbia River.”

The Columbia River used to be further south in what is now known as the Columbia Plateau, she explained, but it got pushed up north as the lava flowed through.

“Then when it comes to Portland and the Willamette Valley,” we moved further down the map, “it makes up the Amity Hills, Eola hills, and Salem Hills.”  Again, these would have been low points, or depressions at the time.

“We find it in the Molalla River in what used to be river valleys,” she continued, and in places like “Silver Falls State Park.”

“Then we see it out here and in the Capes all the way as far south as Seal Rock,” she concluded.

Sheila drawing Oregon in the sand.

A Gap

But there is a problem—a gap if you will. There is not a clear sign of Columbia River Basalt flows through the Coast Range Mountains. How did they make it all the way to Coast near Newport?

This is where Sheila comes in. She has made it her mission to find Columbia River Basalts in the Coast Range Mountains—to trace its path to the Ocean.

Now there is a lot of basalt in the Coast Range Mountains, but the problem is “the chemistry doesn’t match up.”

“A lot of it is Siletz River Basalt,” Sheila said as we restarted our walk back.

Siletz River Basalts are part of a massive igneous province that formed in the Pacific Ocean before accreting to North America beginning about 50 million years ago known as Siletzia or the Siletzia Terrane. This exotic terrane became the foundation for the Coast Range but is also visible in various locations in the Coast Range.

According to Sheila, Columbia River Basalts have “higher silica than most basalt”  and each flow or unit has a specific chemistry. She has collected samples at various promising locations in the Coast Range but has yet to find a match.

Perpetual Teaching and Learning

Sheila and I soon recrossed the creek we had waded over earlier. 

After we crossed, I asked Sheila to tell me about one of her favorite places on the Oregon Coast. She had mentioned Cape Perpetua earlier and I wanted to know the story.

“Cape Perpetua was a personal thing,” started Shiela. “ I was studying oceanography and looking out at the ocean.”

She could see the waves breaking below her and she realized she could calculate how far apart each wave from another using known distances, like the road. The distance of one wave to another where they start to break tells you the depth of the water at that location.

“It came to me,” she went on. “I really love this. I want to do this.”

Sheila paused.

“That was 25 years ago. I haven’t tired of it.”  

We continued our conversation passing through the creek, back up the basalt cobble, and up the paved path to our cars—and Sheila never tired.

And you know what? Neither did I.

Sheila Alfsen is a geology instructor at Chemeketa Community College, Linn-Benton Community College, and Portland State University. She is also a past president and program director of the Geological Society of Oregon Country in Portland. Sheila earned d Bachelor of Arts from Western Oregon University for Geology and Spanish before going on to get an MAT from Western Oregon University.

Hike with a Field Geologist

View of Broken Top and one of the Green Lakes

I am constantly amazed by the power of water to sculpt the landscape. From glacially carved canyons and deep V-shaped ravines to massive floods capable of eroding and depositing sediment over 100s of miles—water in its various forms has shaped the Earth in profound ways.  The impact of water on the landscape can be seen all around us. If we know where to look.

Luckily for me, I arranged to meet up with Hal Wershow, a geologist and expert on reading the landscape, to help me better see and understand water’s influence in the Pacific Northwest. 

Naturally, we headed to the Cascades to a popular hiking spot in Three Sisters Wilderness called Green Lakes.

Hal in his element, enjoying the views and excellent geology!

The Hike

  • Trailhead: Green Lakes Trailhead
  • Distance: 9 miles round trip to first two Green Lakes
  • Elevation Gain: 1,100 ft
  • Details: This trail is very popular and was heavily trafficked until permits were put in place in 2021. A Central Oregon Cascades Wilderness is required from May to September. The trailhead is easily accessible and there is ample parking. A pit toilet is available at the trailhead.

Opening the Flood Gates

The path hastens along next to a fresh flowing creek lined with conifers and dotted with colorful wildflowers.  A few puffy white clouds floated past us overhead as Hal and I began our hike from the Green Lakes Trailhead.

The ground was level with baseball-sized pieces of pumice and other volcanic rocks scattered between bunches of vegetation. “Fluvial is the term we use for sediment moved by water,” explained Hal. The rounded rock and flat ground are signs that water flooded the area in the past.   

This, of course, begs the question—what happened? Short answer—No Name Lake.

You see, No Name Lake was formed by a glacial moraine, or an accumulation of unconsolidated rock, that was carried in and left behind by a receding glacier from the “Little Ice Age” of the 1800s. Then in the 1960s, an unexplained breach in the moraine occurred resulting in a flood. Perhaps some ice or rock had fallen in the lake generating waves that overtopped the dam causing it to fail.

Interestingly, the source of the flood was reported by Bruce Nolf, a geology professor at COCC at the time—a position Hal now occupies.

The waters from that flood would have washed into the area, Hal explained, carrying sediments and debris all the way across the highway we had just driven in on.

Fall Creek flowing through the flat floodplain at the start of the hike.

Snow Going

It wasn’t long before Hal and I, following the creek-side path, entered a more densely wooded area still blanked in snow. It was early summer and winter snow still lingered in large patches on the trail.

Snow accumulation in the Cascades is incredibly important in the Pacific Northwest. As snow melts it seeps into the ground slowly through pores in rock, becoming part of the groundwater. This water eventually escapes back to the surface through springs that feed our streams and rivers. The lag time between precipitation, snowmelt, and water resurfacing is important helping ensure water supply even in the drier parts of the year.

Snow fields were abundant along the trail.

Spring Forward

Hal told me about a project he is doing with his students at CCOC where they are studying the time water spends underground—also called residence time.  Referred to as the “Spring Monitoring Project,” Hal’s students are locating and gathering samples of water from springs in the Central Cascades near Bend. Then they are sending the samples to a lab for stable isotope dating to determine the residence time of each spring.

Stable isotope dating is used for a lot of applications—to date the age of fossils, archeological artifacts, etc. Elements, like carbon and hydrogen, have a different ratio of their respective isotopes depending on conditions and can change over time. For example, all living things contain a ratio of C-12 to C-14 that is constant, but once an organism dies, C-14 will decay predictably, changing the ratio. This change in ratio allows scientists to determine the age of tissue containing artifacts.

Spring water works in much the same way but uses different isotope tracers to figure out how long water has been underground. The time spent underground varies a lot. Water can remain underground for minutes to thousands of years.

“This research is important, especially in the light of climate change,” Hal explained. With increased drought conditions coupled with increasing demands on water resources, it is important that we understand how much water will be available each water year. Springs with long residence times may be more resilient to climate change.

Rushing Waters

Hal and I continued to crunch over frozen hills of snow, watching out for snow bridges, as we continued to pick our way alongside Fall Creek under a canopy of mountain hemlock and fir.

Eventually, we passed by Fall Creek Falls in just a little over half a mile and took a moment to appreciate the raging white waters as they rushed down a short rockface. Fall Creek and its falls are fed by the same waters that fill Green Lakes which, in turn, are fed by glacial and snowmelt from South Sister.

Waterfalls are another example of the force of water on the landscape. Water is an agent of erosion, but not all materials erode equally. For example, most sedimentary rock erodes easily, while others, like igneous rock, granite, are more resistant. Waterfalls, like Fall Creek Falls, form when there is a difference between the materials that make up the streambed. Essentially, the material below the waterfall eroded more easily than the material above it.

We continued to trace Fall Creek’s flow further upstream, the trail trending uphill through some switchbacks, eventually crossing the creek on a narrow log bridge.

Fall Creek Falls as seen from the trail.

Walk on, Rock On

As we walked along the path, Hal pointed out some of the different rocks found along the trail. All the rocks we saw were igneous rocks—formed from cooled magma.  

In general, igneous rocks can be divided into two major groups based on their silica content—mafic rock and felsic rock. Mafic rock is low in silica (45-55% silica) and is generally darker in color. The lava is less viscous (due to its low silica content) and erupts smoothly, as gases readily escape and don’t build up generating the pressure needed for an explosive eruption. Dark grey basalt is a classic example of mafic rock. 

Felsic rock on the other hand is high in silica (65% or higher silica) and tends to be lighter in color. The lava is much more viscous and stickier making it difficult for water and gases to escape. The result is a buildup of pressure and more explosive, violent eruptions. Pale tan or pink rhyolite is a classic example of felsic rock.

Light grey andesite is an intermediary (55-65% silica) between mafic and felsic. Andesite rock has enough silica to produce quartz crystals, so it often has a “salt and pepper” appearance.

Disorganized

However, the chemical composition of igneous rocks is not the only thing that determines their final structure. For example, rocks exposed to oxygen may become redder; rocks that form under the Earth’s surface grow larger crystals; and rocks formed during explosive eruptions may be more fragmented.

One of the most common rocks Hal pointed out on the trail was pumice. Chemically, pumice is like any other rhyolite rock, but because of the conditions it formed in, pumice has some unique qualities. 

Pumice is formed during violent eruptions of very viscous rhyolite lava that is very high in water and gases. When ejected, the gases escape rapidly and the water evaporates and expands, causing the lava to become frothy. Pumice is a disorganized rock—formed so quickly that there was no time for it to crystalize. Hal called it “volcanic glass.”

The resulting rock is an incredibly light, vesicular rock with the reputation of being able to float in water.

Slow your Flow

However, one of the most striking rocks seen on the trail isn’t pumice, but obsidian—a shiny, (usually) black rock, generally known for its use in arrowheads and other edged tools. The cutting edge of an obsidian tool is sharper than a surgeon’s steel scalpel. 

Not too long after crossing Fall Creek, part of the 2,000-year-old Newberry lava flow comes into view—a massive wall of rhyolite—much of it in the form of obsidian. The wall is a spectacular feature for the next few miles, hemming in Fall Creek on the opposite bank from the trail.

The wall of rhyolite starting to come into view.

Hal explained that obsidian, like pumice, is also rhyolite. However, unlike pumice, obsidian is not the result of explosive eruptions, but rather viscous lava that exudes slowly from volcanic vents. Just like pumice and volcanic ash, obsidian has no crystalline structure and is also “volcanic glass.”

Hal described the lava flow as being so slow that the movement would have been imperceptible to the human eye—we are talking less than a few meters per hour.  The flow would have also been cooler and not like the red-hot magma seen erupting from volcanos in Hawaii that tend to be mafic lava flows.

More views of the rhyolite lave flow. The dark, shiny rocks are obsidian.

Lakes O’ Plenty

Hal and I continued to hike uphill through the forest, crossing several smaller creeks as we went. Eventually, we reached a sign with a map indicating we were about to enter the Green Lakes Basin. 

Early in the hike, Hal told me that there were several ways lakes can form. A glacial moraine is one way, like the one that formed Broken Top’s No Name Lake. A lava flow dam is another. Green Lakes is an example of a lava-dammed lake. From the map you could see where the lava flow displaced the creek and cut off most of the area above, creating the basin. 

Hal also pointed out the areas where water is flowing into Green Lakes. Not just water, but sediment too. They are being filled up, Hal explained. The addition of sediment means that Green Lakes will not be around forever.

“Another 1,000 years and they won’t be here,” Hal stated emphatically.  

Stopping to check out the Green Lakes map and sign.

Composite

Past the sign, the first of the Green Lakes comes into view. Flanking the blue-green waters are two massive peaks—South Sister and Broken Top.  Like sentinels, they tower above Hal and me. While at the same time, seemingly close enough to touch.

Both South Sister and Broken Top are stratovolcanoes, also called composite volcanoes—named for the varying nature of erupted materials that build their steep cones—anything from lava to ash. The formation of a stratovolcano is a process of building up and tearing down. They are known for violent eruptions where large amounts of their mass may be ejected into the air—sometimes leaving a large crater. Mount St. Helen’s is a composite volcano. Mt. Mazama, where Crater Lake now stands, is also a composite volcano that blew its top over 7,000 years ago.

South Sister, a relatively young composite volcano.

Fire and Ice

However, as Hal reminded me, volcanism is not the only powerful force at work in the High Cascades. Ice—in the form of glaciers—is also a powerful agent of change in this volcanic landscape.

South Sister, with her tall dome shape retained, is still active—with recent eruptions dating back only a couple thousand years. In contrast, Broken Top is a long-extinct volcano—last active over 150,000 years ago. Since then, Broken Top has been roughly hewn by glaciers leaving its summit a jagged pile of rock and eruption crater exposed. Glaciers are moving ice, capable of abrading and polishing down rock, creating steep-sided hollows, and leaving behind sharp peaks and ridges. Hal pointed out some of the features formed by glaciers on Broken Top, including a cirque, horn, and arete.

Glaciers can still be seen on both Broken Top and South Sister—though they are much smaller and fewer than just a hundred years ago due to anthropogenic climate change. Staring up at South Sister, I asked Hal how to identify a glacier well enough to tell it apart from snowpack. “Crevasses—deep breaks in the ice formed as different parts of a glacier travel at different speeds—are one key difference,” Hal responded.

But Hal also noted that Glaciers can be very difficult to spot. So difficult, in fact, that only a month earlier, a “new” glacier was discovered on South Sister by Oregon Glacier Institute, an organization with the goal of identifying and monitoring Oregon’s glaciers. And by “new,” I mean new to science. “Glaciers tend to be in areas that aren’t very visible,” Hal warned, “making them difficult to locate.” 

Heavily eroded Broken Top

Alluvial Fans

Continuing our hike, Hal and I followed a trail that put us closer to the base of South Sister. Here we reached a deep water crossing and a view of one of the alluvial fans that South Sister’s meltwaters created stretching out in front of us.

An alluvial fan forms when terrain suddenly becomes less steep, like at the base of a mountain, and the water flow less restricted. As the gradient is lowered, the water flow slows and spreads out, dropping sediment in a fan or cone shape.

Earlier in the hike, Hal pointed out a “mini-version” of an alluvial fan where steep flowing drainage of water slowed near the trail as the path of the water flattened and the water was unconstrained. Though perhaps not as dramatic as the large alluvial fan in front of us, the principals are the same. When water slows, sediment drops out.

Hal and I considered crossing the creek to get a better look at the first fan, Hal even attempting to balance his way across some unstable logs, but instead opted for an adventure around the second Green Lake and past the third to the alluvial fan on the far side of Green Lakes.

Hal with a mini-alluvial fan on the trail.
The first water crossing looking out toward an alluvial fan

Round We Go

As Hal and I made our way around the largest of the Green Lakes, we kept a lookout for more geological treasures.

The snow continued to be a bit challenging at times, but we treaded carefully along the narrow trail. 

Before long we spotted signs of an ephemeral spring. Though no water was rushing forth from the Earth, Hal pointed out the eroded channels, changes in vegetation, and exposed roots—all indicators that water had flown forth at some point during the year.

Hal pointing out signs of an ephemeral spring

A bit later, Hal spotted a perfect example of high silica, rhyolite, and low silica, basalt sitting side by side on the trail.

Rhyolite to the left with basalt to the right.

Breach

Eventually, we made it to the bottom of the alluvial fan. Hal explained that there was evidence, at least in part, that the fan was a result of a breach in a moraine-dammed lake further up the mountain. The plan was to head off-trail and follow the alluvium up to see if we could reach the moraine lake.

Almost immediately after heading off-trail, Hal started pointing out the changes in terrain. Like a kid-in-a-candy-store he had me looking at the rock that now littered the ground.  “No pumice!” he exclaimed.

Instead of pumice, the area was filled with volcanic rock that looked speckled—with larger crystals embedded in a finer grain. A “porphyritic texture,” stated Hal—formed from lava that cooled slowly below the surface before rapidly cooling above the surface.

The “fresh rock” signaled to Hal that the lava bed we were walking in was from a different eruption than the pumice and lava flow from earlier.

Fresh volcanic rock!

Signs of a Flood

Hal’s excitement continued as we picked our way up the drainage—the area was literally awash in signs of past flooding.

For one, the size of the rocks changed—smaller rocks gave way to larger rocks—as we moved up. Hal explained that this was expected, as smaller rocks can be carried by the floodwaters farther than larger rocks, which would have been dropped closer to the breach.

Larger rocks also piled up along the edges of the now-empty flood channel—forming natural levees. Again, Hal explained how the energy of the floodwaters would have dissipated toward the edges, dropping these boulders into place.

Hal also noted how the forest looked different in the flood zone. Looking beyond, you could see a lot of taller trees, but within the flood zone, there were only small trees. Trees in the area would have been toppled by the floodwaters. The smaller trees, Hal explained, would have sprouted after the last big flood.

Natural rock levees at the start of our off-trail climb.

Flow Banding and Glacial Polish

Hal and I continued to pick our way over larger and larger rocks. Along the way, we saw some more fun geological features in the rock.

One such feature was a large rock near the edge of our flood channel that looked striped or banded. Hal explained that each band was really the result of different flow rates in the lava that cooled to form the rock—a phenomenon known as flow banding. Flow banding occurs because there is the shearing force between the layers of lava causing them to flow differently relative to one another. 

Hal’s geologist mini-figure sitting atop a flow banded rock.

A bit later, Hal pointed out another rock.  This one was smooth with some well-defined grooves. Unlike the flow-banded rock, the lines in this rock were formed from a glacier. When glaciers pass over rock, Hal explained, they carry gritty sediments that will abrade the rock, polishing the rock smooth.  If a larger rock is stuck in the glacier, it will carve deeper grooves in the rock as well.  The overall effect is called glacial polish. Hal suggested thinking of it like sandpaper—different parts of the glacier may have a different grit resulting in differences in the polish.

Hal pointing out the glacial polish on one of the many boulders along the trail.

Survivor

We continued heading up the rocky drainage, crossing several snowfields. The rock levees are now as much as 10 feet tall in places. Looking back, beautiful views of the Green Lakes Basin periodically caught my attention. 

Apart from the snow, boulders made up most of the ground surface as we trekked upward. The young forest seen toward the base of the washout was nonexistent.  But what we did find were remnants of a vegetative past.

At one point, Hal and I saw a log stuck in the sediment that sparked some interest. Organic material, like the log, can be dated using either radiocarbon dating or dendrochronology. Radiocarbon dating would provide the apparent age of the tree, a decent estimate of age as far as geological events go.

Hal recording video of a log stuck in the sediment.

However, one of my favorite spots on our hike was where we passed a live tree that had somehow survived the floods. Though a bit disheveled, broken and stripped of bark on one side, it was beautiful in its own way. We stopped for a while by this tree, breaking for water. Standing there looking up at its worn trunk I was drawn to its ruggedness. It’s history. It’s story.

A Story

Hal and I never made it to the glacial lake to see the breach. Logistics didn’t allow for it. We did, however, see its effects.

The story of the Earth is one of constant change—often slow but punctuated by quick, sometimes devastating, alternations. Hiking with Hal reminded me of this.

Powerful natural forces that shape the planet, like water, make change inevitable, but also knowable. The story of our planet unfolds as we read the geology. And, like a tree battered by floodwaters, it is one of beauty and resilience.

The survivor!

Hal Wershow is an Assistant Professor of Geology at Central Oregon Community College. His prior experience includes work in the environmental services industry and geoscience education. Hal earned a Master’s in Geology from Western Washington University.

Hike with a Geophysicist

Robert (Bob) Lillie at the summit of Marys Peak

Have you ever wanted to travel back in time to see what the Earth was like thousands or millions of years ago? Well, then this post is for you!

A hike on Marys Peak is like a window into Oregon’s geological past. Marys Peak’s rocks, viewpoints, and vegetation, all paint a picture of large-scale changes that occurred in Oregon millions of years ago, and continue to shape the landscape today.

Hiking with Robert (Bob) Lillie—a geophysicist with a knack for interpreting the Oregon landscape—is like having a tour guide along for the journey.

Armed with a simple model of Marys Peak, rock samples, and two books on Oregon Geology authored by Bob, he met me at the Day Use Area on Marys Peak to begin our hike.

View of Marys Peak from Beazell Memorial Forest’s south meadow.

The Hike

  • Trailhead: Summit Trailhead (Marys Peak Day Use Area)
  • Distance: 3.5+ miles (summit loop trail + meadowedge loop trail)
  • Elevation Gain: approx 700 feet
  • Notes: Northwest Forest Pass is required to park at the Marys Peak Day Use Area where you will find ample parking and pit toilets. There are many additional hiking options on Marys Peak of various length and difficulty.

Marys Peak Rocks

Holding up a labeled bicycle helmet as a model, Bob explained that Marys Peak was made up of several layers of different types of rock, each with unique properties. At the base was black volcanic rock called basalt, followed by thick layers of light colored sandstone and dark shale, and at the top an intrusive rock known as gabbro. This hard gabbro layer, Bob pointed out, is where we would be hiking today.

Bob’s bicycle helmet model of Marys Peak.

Cool Rocks

You may recall from middle school science, that igneous rocks form when lava or magma cools and solidifies.  However, due to differences in formation and chemistry, not all igneous rocks turn out the same. Bob pulled out some rock samples- gabbro and basalt- and began to explain their differences.

Dark-colored basalt is a low-silica igneous rock that forms from thin, fast-flowing lava (think Hawaiian volcanoes) that cools and hardens quickly— within a few hours to days. Gabbro is also dark-colored with the same low-silica chemical composition as basalt, but forms from magma that cools very slowly below ground, taking 10s to 1000s of years to cool and harden.

The long cooling time allows large crystals to form in gabbro rock. On the other hand, basalt has very fine crystals, making it a bit dull looking and less valuable. Thus, gabbro is used in masonry in Oregon, often as a granite alternative, while basalt is used to gravel roadways.

Image Credit: Lillie, Robert. “Oregon’s Island in the Sky: Geology Road Guide to Marys Peak.” Wells Creek Publishers, 2017.

Putting the rock samples away, Bob and I followed the gravel road part of the summit loop trail upward from the parking lot. Eventually, we reached some gabbro outcroppings, with large crystals glimmering in the sunshine. 

Heading up the summit trail to the first set of gabbro outcroppings

Weathering Time 

Remember, gabbro forms below ground. According to Bob, two miles of sedimentary layers once covered the now exposed gabbro rock. Of course, that was millions of years ago. So what happened? Where did the sedimentary layers go?

The answer lies in one of the most underappreciated geological processes— weathering an erosion. Weathering is the breakdown of rock by contact with the atmosphere, hydrosphere, and biosphere. Basically, exposed rocks get worn down over time with a little help from the environment.  This weathered material can then be eroded (moved away by wind and water), uncovering more rock that lies below. Sedimentary rock weathers and erodes easily, while igneous rock such as gabbro is much harder. 

 “Look up,” Bob exclaimed, “imagine two miles of sedimentary rock pushing down from above you.” 

The slow action of weathering and erosion removed it all! What a load off!

Mini-Yosemite 

As we hiked along the gabbro rock gardens, Bob pointed to some rounded outcroppings of gabbro rock that reminded me of pillow basalt— a form of basalt that results from cooling in water. Though pillow basalt can be viewed on the road up to Marys Peak, it made no sense that we would find it here in the gabbro layer. Something else was going on! Bob explained that the answer lies in a process known as spheroidal exfoliation.

With the slow removal of the weight of two miles of sedimentary rock layers, the gabbro sill would have fractured and broke into cubed or rectangular blocks. Then, spheroidal weathering would have taken over—discriminately breaking down the gabbro blocks; wearing down corners more than edges, and edges more than faces; and eventually forming rounded spheres surrounded by concentric “shells” flaking off.  Once exposed, these layers may erode and “peel” away layer by layer—much like peeling away the layers of an onion.

Spheroidal exfoliation on a gabbro outcropping

Bob compared the rounded rocks on Marys Peak to the huge granite domes (such as Half-Dome) you can see in Yosemite National Park. The same basic mechanisms of exfoliation apply, just on a different scale. Thus, Bob dubbed Marys Peak a “mini-Yosemite” in honor of the striking resemblance.

Hard as a Rock

At about 500 feet above the rest, Marys Peak is the highest mountain in Oregon’s Coast Range. In part, Marys Peak stands out above the other mountains because it is hard-headed or, as Bob puts it—stubborn! Compared to the sedimentary rocks that once covered it, the gabbro on top of Marys Peak is very resistant to weathering and erosion. The stubborn gabbro thus acts as a sort of shield to the elements, allowing the peak to remain prominent.

Image Credit: Lillie, Robert. “Oregon’s Island in the Sky: Geology Road Guide to Marys Peak.” Wells Creek Publishers, 2017.

Island in the Sky 

The fact that Marys Peak is “stubborn, has essentially allowed it to maintain its height and, in turn, a cold subalpine climate. Marys Peak, as Bob describes, is “an island in the sky.” 

With colder, harsher conditions than other coastal mountains, Marys Peak exists as a remnant of the past. Rather than the typical Coast Range Douglas-fir/hemlock forest, Marys Peak is a botanical anomaly, and a very beautiful one—it has even been designated a Scenic Botanical Special Interest Area.   

The meadows, rock gardens, and noble fir forests that make up the upper reaches of Marys Peak are unique to the Coast Range today, but once would have been typical of the region. Botanically speaking, Marys Peak is living in the last ice age that ended about 12,000 years ago. Many subalpine wildflower species are found here. During our hike through the rock garden, Bob and I took note of several: harsh Indian paintbrush, spreading phlox, Cascade desert parsley, and Cardwell’s penstemon, to name a few; and in the meadows- glacier lilies.  

A gabbro wildflower rock garden on Marys Peak

Marys Desert?!?

But subalpine flowers were not the only botanical anomaly of note on Marys Peak. As we hiked farther up the summit trail, past most of the rock gardens, Bob pointed out a slightly lower ridge to the left on the south flank of the mountain.  Here we found another remnant of the past—a veritable desert!  

Some 6,000 to 4,000 years ago, during a warm, dry period, species still found today in the eastern or southern parts of Oregon spread into parts of western Oregon.  Later, as the climate again shifted toward cooler and wetter, most of these—what are known as xeric species—retreated back.  But this outcropping- with it’s thin, rocky soil (thanks again to stubborn gabbro) and it’s harsh, drying winds- held onto its xeric species. The west-facing of this area is especially important because high winds coming from that direction blow away most of the heavy snow blanket that covers other areas near Marys Peak summit. 

I was unable to see or identify xeric species from where I stood, but prostate lupine (eastern Oregon species) and sulfur flowered buckwheat (southern Oregon species) are apparently two xeric species to keep an eye out for. 

Marys Desert—A xeric rock garden (desert ecosystem) on the west-facing slope of Marys Peak  

Story Beneath the Scenery

About ½ mile from the start of the trail, we reached the summit of Marys Peak. Ignoring the unsightly communication towers behind us, we looked out into the horizon. The views on Marys Peak are reason number two for visiting—come for the wildflowers, but make sure you stay for the viewpoints (and the geology)!  

From the summit, looking to the west, you can see the Pacific Ocean; and to the east the Cascade Volcanoes are prominently on display, with the Willamette Valley in the foreground. With such scenery, it is easy to get caught up in the simple beauty of Oregon.

It’s also the perfect opportunity to start thinking like a geophysicist—which, according to Bob, involves observing the landscape and visualizing what happened beneath Earth’s surface to cause it.  Much of geology happens slowly. We can’t watch changes occur, but we can use what we do see to develop inferences regarding the past. Like watching the final scene in a movie, it isn’t too difficult to deduce some of the earlier scenes if you are paying attention.  As Bob puts it- “there is a story beneath the scenery.”  

Views from the summit of Marys Peak

Moving Plates

The Earth is composed of about 12 hard tectonic plates that move around on a softer part of the mantle, called the asthenosphere. These plates grind past one another, and they grow and shrink as they move toward, under, and away from each other.  The motion is messy, resulting in cracking and folding, as well as earthquakes and even volcanic eruptions. These large-scale motions help explain much of Earth’s formations, including those visible from the top of Marys Peak. 

Born in the Ocean

Marys Peak did not start out as a peak. Rather, Marys Peak, and the Coast Range in general, started out as rocks and islands scattered about in the Pacific Ocean. What is now Oregon did not exist 200 million years ago! Over long periods of geological time, the North American plate bulldozed these rocks and islands off the ocean floor, and in the process built Oregon.  

As Bob explained, Oregon sits along a convergent plate boundary, where the North American and Juan de Fuca plates have been colliding for millions of years. More importantly, due to differences in density, the oceanic Juan de Fuca Plate has been diving beneath the continental North American Plate—a process known as subduction.  

But subduction is not a clean or smooth process.  Anything massive that doesn’t fit under North America is scraped off the oceanic plate and added to the continent. These masses of land, called exotic terranes, are responsible for a good portion of Oregon’s land mass, including Marys Peak and most of the coast range.  

In the case of Marys Peak, the basalt lava flows and overlying sedimentary rock layers formed in the ocean.  Later, as the oceanic plate subducted beneath the western edge of Oregon, magma intruded into these rock layers, forming vertical dikes and horizontal sills of gabbro (like the one that forms the “stubborn” caprock of Marys Peak). As the plate convergence continued, a large block of rock was thrust upward and eastward along the Corvallis Fault. Marys Peak was born!  

The other Coast Range mountains visible from Marys Peak summit are similarly composed of volcanic and sedimentary rocks from the ocean that were thrust upward and over the edge of the continent. And like Marys Peak, many of the other high Coast Range mountains are capped by hard, intrusive gabbro. 

Image Credit: Lillie, Robert. “Oregon’s Island in the Sky: Geology Road Guide to Marys Peak.” Wells Creek Publishers, 2017.

Volcanic Peaks

Marys Peak is not a volcano, but from Marys Peak you can see a great many volcanoes. From our vantage point, Bob and I were able to see Mt. Hood, Mt. Jefferson, and the Three Sisters; and, later in the day, Three Fingered Jack, Mt, Washington, Mt. Bachelor, and Diamond Peak. On clearer days you can also see Mt. Rainer, Mt. St. Helens, Mt. Adams farther north; and Mt. Thielsen, Mt. Mazama (Crater Lake), and Mt. McLoughlin to the south. Marys Peak offers views of most of Washington’s and Oregon’s great Cascade Volcanoes! 

I love the Cascade Volcanoes and can’t help but smile anytime I can see them off in the distance. But why are they there? Is there a story beneath the scenery? 

Don’t Sweat! 

Yep! Once again, plate tectonics provides an explanation.

When an oceanic plate subducts, as is occurring off the Oregon Coast today, it starts to sweat!  At about 50 miles below the surface the plate is under so much heat and pressure that it begins to metamorphose and dehydrate. The hot water released reacts chemically with overlying rock, causing it to melt and generate magma. The result is the starting material for repeated volcanic eruptions. 

For the last several million years, the Cascade Volcanoes have been fed by the magma generated by the subduction of the Juan de Fuca Plate below the North American Plate.  The volcanic peaks have erupted countless times during this time period, building up their cone shapes with each eruption.  Though it may seem infrequent on a human timescale, eruptive periods are frequent- with more than 100 Cascade eruptions over the past few thousand years.  As long as subduction continues, the Cascades will continue to erupt. 

Image Credit: Lillie, Robert. “Oregon’s Island in the Sky: Geology Road Guide to Marys Peak.” Wells Creek Publishers, 2017.

The Dynamic Duo: Uplift and Erosion

As Bob pointed out, while tectonic activity is building up volcanoes and lifting up mountains, the other half of a dynamic duo is tearing it all down. The effects of erosion can also be observed at the summit of Marys Peak. 

The Marys Peak region once had an additional two miles of sedimentary rock sitting on top of it!  As the land was lifted up, wind, rain and snow were, at the same time, wearing it down. Sedimentary rock is easily eroded, but Marys hard-headedness—aka her gabbro top—is a big reason she remains tall today. 

The effects of erosion can also be be observed in the Cascade Volcanoes.  When volcanoes become inactive and are no longer being built up by eruptions, they start loosing their tops.  Mt. Washington and Mt. Thielsen are great examples of this. Their pointy tops suggest they haven’t erupted in a really long time, as glaciers have etched away their smooth cones. Yes, even volcanoes show signs of aging!  One the other hand, Mt. Hood’s symmetrical cone shape is a good indicator of “recent” volcanic activity. 

Story of People

After spending several minutes at the top of Marys Peak discussing the “story beneath the scenery,” Bob and I continued our hike, moving downward along the summit trail until we reached the Meadowedge trail junction. Here we took a left and followed the Meadowedge trail. 

Toward the end of that loop, Bob stopped me, suggesting one more time we read the landscape. 

 “What do you see?” He said. 

I looked out across a rolling meadow. But with thoughts of plate tectonics running through my head, I overlooked what he wanted me to see. Finally, he pointed it out- a stage!  

Following WWII, a group known as the Shriners began holding an annual fundraising event on Marys Peak known as the Marys Peak Trek. Each year thousands of people attended to enjoy food and entertainment. One of the meadows even became a parking lot. The damage was extensive. But by 1983, the Trek ended, and the meadows have had some time to start to recover. Even the earthen stage is easy to miss if you aren’t looking for it.  

The Shriners Trek stage.

Bob and I ended our hike by completing the meadowedge loop back to the summit trail, where we hiked through Noble fir forest back to the parking lot where we said our goodbyes.  

Back to the Future

I am not ready to say goodbye to Marys Peak.

Marys Peak still faces many challenges. Rare meadows have been encroached on by Noble fir forest, at least in part due to human disturbance. Social trails and wildflower gathering remain a constant threat to the meadows. And then there is climate change, threatening the very existence of this ice-aged ecosystem.

However, there are also many forces working to preserve Marys Peak. Meadows are being restored and Noble fir populations kept in check. Signs and barriers mark sensitive areas. And many local community groups, like the Marys Peak Alliance, are working to educate visitors on the ecological and cultural importance of Marys Peak.

As we look forward to the future of Marys Peak, it is my hope that it remains as it is today: a future set in the past.

Dr. Robert J. (Bob) Lillie is a free-lance writer, science communicator, and interpretive trainer. Bob was a Professor of Geosciences at Oregon State University from 1984 to 2011. He studied geology at the University of Louisiana- Lafayette and Oregon State University while earning his bachelors and masters degrees, and later studied geophysics at Cornell University where he earned his Ph.D. 

Bob has written extensively about Pacific Northwest geology in “Beauty from the Beast: Plate Tectonics and the Landscapes of the Pacific Northwest” and “Oregon’s Island in the Sky: Geology Road Guide to Marys Peak.” Both books are available at area bookstores, museums and visitor centers, as well as on amazon.com

Curious at Coyote Wall

View from Coyote Wall of Mount Hood and the Columbia River

A Plethora of Curiosities

One of my favorite hikes in “The Gorge” takes you through a Missoula flood inflicted scablands of oak and pine, up a ridge of columnar basalt, and through fields of wildflowers.  Oh and did I mention, views of Mount Hood and the Columbia River. There is a lot to appreciate along the Coyote Wall trail near Bingen, Washington. So today, let’s explore a few trail curiosities that can be found along the Coyote Wall trail. 

The Hike at a Glance

  • Trailhead: Coyote Wall Trailhead
  • Distance: 7.8 miles
  • Elevation Gain: about 1900 feet
  • Notes: No parking pass required, but popular trail so get here early.  Trail is shared with mountain bikers. Pit toilet at the trailhead.  

The Wall (not just a Pink Floyd Album)

One of the most obvious and interesting curiosities to discover at Coyote Wall is the wall itself.  Formed from ancient lava flows that flooded the area about 16 million years ago, the resulting basalt rocks underwent folding and faulting, and later uplift (both of which continue today), creating this magnificent geological feature. You can see Coyote Wall from the parking lot and again later when you climb up and back down it.  It truly is a wonder and a highlight of this hike. 

If you are so Inclined

You see, Coyote Wall is part of the Bingen Anticline- where the earth’s crust has been compressed, folded and uplifted by faulting. The Columbia River corridor east of Hood River is characterized by convex ridges (anticline) and concave valleys (synclines) formed from a north-south compression of the Earth’s crust. To understand how this works, take a flat piece of paper, or other flexible material, and bring its opposite ends together- the paper will “deform” much like the deformation of the Earth’s crust under similar strain.

As part of the Yakima Fold Belt, the Bingen Anticline is asymmetrical. Thus the Coyote Wall ridge is relatively short (maybe a mile or two), compared to the larger associated syncline valley that the town of Mosier occupies across the river (syncline valleys in the area tend to be 10s of miles).  But don’t let it’s length fool you, uplifted Coyote Wall is a steep climb and descent having been uplifted a couple hundred feet! 

Looking back at Coyote Wall

The Labyrinth (not just an 80’s cult classic)

The Labyrinth

But let’s not get ahead of ourselves- first is the Labyrinth!  Before beginning the steep climb up Coyote Wall, a trail to the east leads you through another fascinating geological feature- a channeled scablands. Curiosity number two!  

Throughout southeast Washington, channeled scablands dominate the landscape. Basically, channeled scablands are areas where parts of the soil and bedrock have been torn up, leaving exposed rocks and deep ravines. How did these scablands form?  What happened here? You might have guessed it- water! And lot’s of it.  

Sculpting with Water

During the last ice age 10,000 to 20,000 years ago, massive floods scoured the landscape. At that time, the Cordilleran ice sheet covered large swaths of North American- but it wasn’t static. This ice sheet would periodically inch its way southward, creating an ice dam along the Clark Fork River in Montana.  The water behind the dam would accumulate into a large lake, the massive Glacial Lake Missoula. At roughly 2,000 feet deep, it held about 500 cubic miles of water. Then, periodically, the ice dam would fail, releasing torrents of water and ice. The flood waters tore through Washington and Oregon eroding much of the landscape and depositing materials as far south as the Willamette Valley. 

With many areas of exposed basalt and butte-and-basin topography, the Labyrinth offers a glimpse into the powerful force of these episodic floods.

Wild about Wildflowers

Desert Parsley – Lomatium

Finally (but not least), are the wildflowers!  I am a huge fan of wildflower hikes- and Coyote wall puts on a gorgeous show starting in the early spring.  Among my favorite of the early bloomers (sometimes seen as early as February) are a diverse group of carrot family plants commonly called Desert parsley.  I don’t know how many species of Desert parsley, or Lomatium, can be found along the Coyote Wall trail. But I saw a couple species on my recent visit, and I am pretty sure there are many more- as there are over 70 known species in the west.  Rumor has it they can be difficult to identify. To be honest, I didn’t even try. 

Better than Carrots

Anyway, besides being beautiful to look at, Lomatium also has an interesting history. The tap root of many Lomatium species was both food and medicine to many Pacific Northwest tribes. For example, the Yakama, who once occupied SE Washington, would use the root of Lomatium, also called biscuitroot or kowsh (yes, there are a lot of names for this stuff), to make small biscuits.  The starchy roots of Lomtium were mashed, shaped, and dried in the sun. Then the biscuits were stored for later use.   

I Think… Probably?

Early reports of Lomatium came from none-other-than Merriweather Lewis and William Clark.  Lewis and Clark called the biscuits derived from the root “chapelel bread” and witnessed its preparation and trade. They also reportedly obtained and consumed some chapelel during their journey.  In addition, Lewis collected and described five Lomatium species for his herbarium. Although it seems he too had difficulty distinguishing between species- using qualifiers in his records such as “I think” or “probably” when attempting to identification.  I’m glad I am not the only one. Though the purple Lomatium pictured below is Columbia desert parsley, Lomatium columbianum… “I think… probably.” 

Lomatium columbianum

Get Curious and Explore

In any event, from huge lava flows to massive floods of water to fields of edible vegetation, there is a lot of science and historical curiosities to explore at Coyote Wall.  Botanically and geologically interesting, it is worth a visit. Stay curious!

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