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Smith Rock State Park –great geology at the edge of Oregon’s largest caldera

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Smith Rock, the Crooked River, and modern Cascade volcanoes from Misery Ridge.

The view from outside the small visitor center at Smith Rock State Park offers a landscape of contrasts. The parking lot, and nearby camping and picnic areas, are flat, underlain by the edge of a basaltic lava flow that drops off in a series of steps to a narrow canyon, some 120 feet (37 m) below. The Crooked River, which rises about 100 miles (162 km) away in the High Lava Plains, fills much of the canyon bottom. Across the canyon, tan cliffs and spires of tuff, another volcanic rock, soar overhead. Smith Rock itself forms a peninsula of this rock, enclosed by a hairpin bend of the Crooked River. The tuff erupted 29.5 million years ago in the largest volcanic eruption to occur entirely within Oregon.

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View down the Crooked River from near the parking lot. On the left is the Newberry basalt flow; the reddish tower just right of the river is the rhyolite dike intruding the Smith Rock Tuff.

The eruption created the gigantic Crooked River Caldera, which stretches like an ellipse southeastward from Smith Rock more than 20 miles (32 km) and traversed along its length by the Crooked River. Around its perimeter are rhyolite bodies that intruded after the eruption along ring fractures surrounding the caldera. These rhyolites include Gray Butte, just north of the park, Grizzly Mountain, to the northeast, and Powell Buttes, some 15 miles (24 km) to the southeast. The imposing red-colored tower, just downstream from the hikers’ bridge in the state park, is a rhyolite dike that also intruded after caldera collapse.

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Geologic maps: of Smith Rock State Park (left) and the Crooked River Caldera (right). Compiled from McClaughry et al. (2009A), Robinson and Stensland (1979), Walker and MacLeod (1991), and the State Park trail map.

Some of the finer-grained, airborne material likely accumulated 75 miles to the east to form much of the green-colored Turtle Cove Member of the John Day Formation, which has the same age. All told, the eruption produced more than 140 cubic miles (580 km3) of material. The eruption size as well as its caldera, however, eluded detection until about 2006 when Jason McClaughry and Mark Ferns of DOGAMI completed detailed mapping of the region. Now, some researchers even consider the eruption to be an early phase of the Yellowstone hot spot!

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Much of the green Turtle Cove Member of the John Day Formation, so well exposed at John Day Fossil Beds National Monument, was probably derived from alteration of ash derived from eruption of the Crooked River Caldera, 29.5 million years ago.

Hiking any of the state park’s numerous trails gives you plenty of chances to see the rock close-up. It’s pretty much all tuff, the volcanic rock made mostly of consolidated ash and pumice. Many tuffs become welded into hard rocks because of the high temperatures as they compact, but most of these tuffs are not welded and so relatively soft. Some exceptions include the red-colored welded tuffs at the crest of the Misery Ridge trail.

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Close-up view of the Smith Rock Tuff. The faint green layers contain a higher proportion of fine ash, whereas the intervening areas typically contain coarser ash and more pumice. The greenish color consists of the alteration mineral celadonite.

You might also notice that parts of the cliffs display layering inclined roughly southward. Up-close, you can see that some layering is defined by subtle changes in the proportions of fine to coarse ash to suggest variations in the ferocity of the eruption. Many layers contain small rock fragments, the rocks being older material incorporated into the eruption. Most of these rocks are volcanic, derived from the underlying Clarno Formation. A tiny fraction, however, are pieces of Permian-age limestone. These limestones are significant as they came from the basement rock, accreted to North America during the later Jurassic or early Cretaceous periods.

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Fine-scale layering in the Smith Rock Tuff

Numerous pocket-like holes dot many of the cliff faces. The outer edges of these features typically consist of more durable rock whereas the insides typically consist of softer, more easily erodible material. The durable crusts form because minerals in the tuff dissolve in pore water and re-precipitate on the surface as the pore water evaporates. At Smith Rock, the responsible minerals are mostly zeolites, a group of minerals with wide-ranging compositions but containing silica, aluminum, and water. Along with the enhanced weathering and erosion along fractures, this case-hardening results in an endless variety interesting shapes and pinnacles.Case-hardening in tuff

The case hardening also creates outstanding surfaces for climbing, so on sunny weekends, the state park draws hundreds of rock climbers of all abilities. Considered one of Oregon’s top climbing areas, Smith Rock offers more than 1500 routes. Moreover, the cliffs are recognized as the birthplace of American sport climbing, which unlike traditional climbing, benefits from anchors placed permanently in the rock

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Rock climber reveling in a crack on the pillar called “Monkey Face”. Note the reddish upper part of the rock –it’s welded tuff above the non-welded tuff. Note also the layering in the tuff.

IMG_2255lrcThe basaltic lava flows at the state park have their own story, as they originated from vents on the north side of Newberry Volcano some 400 thousand years ago. If you look closely at the basalt, you’ll see that it’s uniformly very finely crystalline, but in some places full of air bubbles called vesicles. Because gases tend to rise through lava flows, the vesicles tend to become larger and more abundant towards the top of individual flows–as shown in the photo on the left –although you really need to click on it to see the larger version. The photo is 4 feet high from bottom to top.

For the most part, the lavas covered the older Smith Rock Tuff. They blanket the southwestern part of the caldera and sit on top the tuff in many places within the canyon. However, the cliffs of Smith Rock soar far above, so the lavas had to flow around them on their way to the Deschutes Canyon, some ten miles to the northwest. The interface between the high-standing tuff and the basaltic lava must have been highly irregular to make it ripe for erosion by the Crooked River, which now meanders through a lovely gorge.

And this post! It’s a draft of an entry I’m planning for my upcoming book, “Oregon Rocks!” –to be published by Mountain Press, probably sometime in 2021. I’m only allowed a few photos per entry, so here are a few more! You can click on each to see them at a larger size.


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Newberry Basalt overlying Smith Rock Tuff on the west side of the Crooked River, just downstream from its hairpin bend. Note the channeled base of the basalt.

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Lithic (rock) fragments in the tuff

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View northward from the west side of Misery Ridge, showing the red-colored welded part of the tuff overlying the less welded part.

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Contact of ash-and pumice-rich tuff overlying lithic-rich tuff near the bottom of the Misery Ridge Trail.

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View upstream: tuff on the left and in the background; basalt in the right middleground.

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Some useful references:

Bishop, E.M., 2003, In search of ancient Oregon: Timber Press, Portland, 288p.

McClaughry, J.D., Ferns, M.J., Gordon, C.L., and Patridge, K.A., 2009A, Field trip guide to the Oligocene Crooked River caldera: Central Oregon’s Supervolcano, Crook, Deschutes, and Jefferson Counties, Oregon, Oregon Geology, v. 69, p. 25-44.

McClaughry, J.D., Ferns, M.L., Streck, M.J., Patridge, K.A., and Gordon, C.L., 2009B, Paleogene calderas of central and eastern Oregon: Eruptive sources of widespread tuffs in the John Day and Clarno Formations, in O’Connor, J.E., Dorsey, R.J., and Madin, I.P., eds., Volcanoes to Vineyards: Geologic Field Trips through the dynamic landscape of the Pacific Northwest: Geological Society of America Field Guide 15, p. 407-434.

Miller, M.B., 2014, Roadside Geology of Oregon: Mountain Press, Missoula, 386p.

Robinson, P.T., and Stensland, D.H., 1979, Geologic Map of the Smith Rock Area, Jefferson, Deschutes, and Crook Counties, Oregon. US Geological Survey Miscellaneous Investigations Map I-1142. 1:48,000.

Walker, G.W., and MacLeod, 1991, Geologic Map of Oregon. US Geological Survey. 1:500,000.

And some links:
Smith Rock State Park: https://oregonstateparks.org/index.cfm?do=parkPage.dsp_parkPage&parkId=36

Climbing article: https://www.climbing.com/places/thanks-volcanoes-climbing-in-oregon/

Just scratching the surface. A geologic cross-section of Oregon speaks to unimaginable events.

The cross-section below runs from the Cascadia subduction zone across Oregon and into eastern Idaho.  It outlines Oregon’s geologic history, beginning with accretion of terranes, intrusion of granitic “stitching plutons”, and deposition of first North American-derived sedimentary rocks, and ending with High Cascades Volcanic activity and glaciation.

Schematic geologic cross-section across Oregon, from the Cascadia Subduction zone into western Idaho.

Schematic geologic cross-section across Oregon, from the Cascadia Subduction zone into western Idaho.

The cross-section barely scratches the surface of things. Moreover, it boils everything down to a list, which is kind of sterile. But the cross-section also provides a platform for your imagination because each one of these events really happened and reflects an entirely different set of landscapes than what we see today.

Think of the CRBG about 15 million years ago. The basalt flows completely covered the landscape of northern Oregon and southern Washington. Or the Clarno volcanoes –only a part of the green layer called “Clarno/John Day”. They were stratovolcanoes in central Oregon –when the climate was tropical! Or try to wrap your mind around the accreted terranes, some of which, like the Wallowa Terrane, contain fossils from the western Pacific.

To emphasize this point, here’s Crater Lake. Crater Lake formed because Mt. Mazama, one of the Cascades’ stratovolcanoes, erupted about 7700 years ago in an eruption so large and violent that it collapsed in on itself to form a caldera. It’s now a national park, with a whole landscape of its own. And if you visit Crater Lake, you’ll see evidence that Mt. Mazama had its own history –which dates back more than 400,000 years. But Crater Lake and Mt. Mazama make up just a tiny part of the Cascades, which are represented on this diagram by just this tiny area that’s shaped like a mountain.

Crater Lake occupies the caldera of Mt. Mazama, which erupted catastrophically some 7700 years ago.

Crater Lake occupies the caldera of Mt. Mazama, which erupted catastrophically some 7700 years ago.

So the cross-section is kind of sterile and just scratches the surface. But what makes geology so incredible is that we’re always learning new things and digging deeper –and we know we’re just scratching the surface –that there will always —always— be something  to learn.


click here and type “Oregon” into the search for photos of Oregon Geology.
click here for information about the new Roadside Geology of Oregon book.

Crater Lake caldera, Oregon –some things happen quickly!

Crater Lake never ceases to amaze me.  It’s huge –some 6 miles (10 km) across, deep –some 1700 feet deep in parts –the deepest lake in the United States and 7th deepest on the planet– incredibly clear, and really really blue.  And for volcano buffs, one of the best places ever!

Crater Lake as seen from The Watchman.  Wizard Island, which formed after the caldera collapse, occupies the center of the photo.

Crater Lake as seen from The Watchman. Wizard Island, which formed after the caldera collapse, occupies the center of the photo.

Crater Lake is a caldera, formed when ancient Mt. Mazama erupted so catastrophically that it emptied its magma chamber sufficiently for the overlying part of the mountain to collapse downward into the empty space.  That was about 7700 years ago.  Soon afterwards, Wizard Island formed, along with some other volcanic features that are now hidden beneath the lake–and then over the years, the lake filled to its present depth.  It’s unlikely to rise any higher because there is a permeable zone of rock at lake level that acts as a drain.

Here’s one of the coolest things about the cataclysmic eruption: Not only was it really big, but it happened really fast.  We know it was big because we can see pumice, exploded out of the volcano, blanketing the landscape for 100s of square miles to the north of the volcano –and we can see the caldera.  We can tell it happened quickly because the base of the pumice is welded onto a rhyolite flow that erupted at the beginning stages of the collapse; the rhyolite was still HOT when the pumice landed on it!  You can see the welded pumice on top the Cleetwood Flow along the road at Cleetwood Cove.

pumice welded onto top of Cleetwood rhyolite flow at Cleetwood Cove.  Note how the base of the pumice is red from oxidation --and forms a ledge because it's so hard.

pumice welded onto top of Cleetwood rhyolite flow at Cleetwood Cove. Note how the base of the pumice is red from oxidation –and forms a ledge because it’s so hard.  Pumice blankets the landscape all around Crater Lake.

Crater Lake though, is so much more than a caldera –it’s the exposed inside of a big stratovolcano!  Where else can you see, exposed in beautiful natural cross-sections, lava flow after lava flow, each of which erupted long before the caldera collapse and built the original volcano? Within the caldera itself, these flows go back 400,000 years–the oldest ones being those that make up Phantom Ship –the cool little island (some 50′ tall) in Crater Lake’s southeast corner.

Phantom Ship, in Crater Lake's southeast corner, is made of the caldera's oldest known rock, at 400,000 years old.

Phantom Ship, in Crater Lake’s southeast corner, is made of the caldera’s oldest known rock, at 400,000 years old.

I can’t resist.  The caldera formed about 7700 years ago, incredibly recent in Earth history–incredibly recent in just the history of Mt. Mazama!  To a young earth creationist though, that’s 1700 years before Earth formed.  Now THAT’S amazing!


Click here if you want to see a Geologic map of Crater Lake.
Or… for more pictures of Crater Lake, type its name into the Geology Search Engine.  Or… check out the new Roadside Geology of Oregon book!

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