Volcanic Ramblings Part 6: Cascades Slop Over Into Basin and Range

We managed to consistently get started at a decent time each day of the trip, aiming to gather for breakfast at 8:00. Since we had driven about an hour south from the turn-off to Crater Lake, that meant we had to drive an hour north- though I recently realized there IS a more direct, probably significantly shorter route that would have taken us to the SW entrance. But wait'll you see the juicy outcrops we would have missed in that case!

Descending into the Klamath Basin, numerous ~N/S normal faults have opened up some terrific exposures I had never bothered to look at carefully- though the next one (after this) in particular is one I've wistfully watched as I sailed past it more times than I care to count over the decades. But here's the thing: the rock is steep, not particularly competent, so mass wasting into the road is commonly a problem, route 97 is sort of shoehorned in there where it fits, often with little space for pull-outs or break-down lanes... and it's a fast, busy and dangerous road. So opportunities to geologize need to be chosen carefully, with an eye toward safety.

All that said, we did find a few pre-park stops which, though they chewed up and spat out enormous amounts of precious time (the commodity which was in shortest supply for the whole trip), were definitely worth it. For most of the stops on the trip, I tried to remember to take a shot or two of helpful landmarks for anyone else who would like to check the spots out for themselves someday, and so I could more confidently and precisely find them in Flash Earth. The lead photo above is the intersection of Algoma Road with Route 97. We were able to get off the road, park in a pull-out on the south side, get behind the Jersey Barrier (which was very nice to have between ourselves and traffic), and walk a hundred yards or so south to an interesting-looking face we had noticed only moments before.

Here's the first shot of the day ( Note that all the photos in this series will get much larger with a click.):So what are we looking at? Well, that there is an itty-bitty normal fault in poorly sorted, extremely immature volcaniclastic sand (mostly) and silt. The grains looked to be mostly lithic, which is why I describe it as "extremely immature." The offset looks to be about an inch. Here's a view from a different angle:Isn't that purty? I'm quite fond of sed structures, both original and soft deformation, so I keep an eye out for them at stops like this. Not much of note at this one, but enough to convince me this stuff was reworked by water, not just air fall ash. (Obligatory admission: I'm no expert, and I'm always open to correction and/or questioning.)
Backing off from the same spot, with the lovely Dana Hunter for scale, you can get a better sense of the over-all look of the outcrop, and see that the fault is roughly parallel to the cliff face, suggesting this is a subsidiary fault to the much larger one that created this escarpment.Looking a bit farther along, there's a lens of very dark sediment that I took to be a small cut-and-fill structure at the time, but it occurs to me it might be a small channel from near the start of this sedimentation cycle. The next unit down is a brick red layer that looked as if it might be a thick ash-fall unit. Looking south along the face, below, it's quite striking. But at the far end, you can see the same kind of stratification as above the brick red stuff.
Walking south, down-section, more of the same under the bricky stuff...
Turning to look north, yep, it's pretty clear that structurally, we're in basin and range. I would guess (and later 65 mph reconnaissance geology seemed to confirm) that the sorts of rocks and sequences we're seeing here would be up there, too.Below, a block of stretched-vesicle mafic rock that fell from a lava flow above the sediments first shown with the fault...
...and a coarse cobbly layer in the lower section of sediment.
So what can we say about this environment (dons semi-irresponsible speculation helmet)? Well, it's very clearly dominated by a nearby source of volcanic rocks... oh, I didn't show you the view across the highway yet, did I?That'd be Mt. McLoughlin, the southernmost major Cascade peak in Oregon. (I doubt that particular volcano contributed much to this outcrop, though.) But I have to admit, I'm not very confident describing the depositional environment. I'm guessing that we're looking at a braided stream drainage, mostly choked with ash, but with larger channels carrying flows competent enough to move larger boulders. The material is too coarse and poorly sorted to be lacustrine (as the modern-day lake across the road) but I'm not seeing enough in the way of cross bedding and channel features to feel comfortable with what I'd consider a more typical meandering fluvial environment. There are quite a few flows in between thick piles of sediments, so we're not so far from the vents that sufficiently fluid lavas couldn't reach this spot, but they're a fairly small proportion of the pile... less than a quarter for sure, maybe closer to 10-15%.

In terms of age, I really don't know, but I'd bet pre-Pleistocene, because the magnitude of the fault offsets (which post-date the sedimentation) would require at least one or two million years.

One last shot, taken as we crossed the causeway in the lead photo, with a question for Callan Bentley... what was the term for a ramp between two vertically offset blocks? You mentioned it in your posts on structure in the Bishop Tuff. Followup: Callan responds swiftly with the response "relay ramp." That there below is one.

Volcanic Ramblings Part 5: Lotsa Lakes

Looking across Odell Lake to Diamond Peak

I have read several times, in sources that look to be reputable, that the rate of ecological change from the Cascade Crest down into central Oregon is one of the most rapid in the terrestrial (as opposed to marine) world. I'm always suspicious of any claim of unique extremity- who says it's the biggest/tallest/deepest/smallest? But if you watch the change in trees and underbrush from Salt Creek Falls to route 97- the N/S backbone of central Oregon- it really is quite amazing how rapidly and thoroughly the forest changes, not just once, but multiple times. Just west of the crest, I would guesstimate annual precipitation is around 150 inches per year; by the time you get out onto the east side apron, it's closer to 25. The dominant trees grade from enormous DouglasFir, with lush and abundant undergrowth, to Ponderosa Pine, Lodgepole Pine, then sagebrush and juniper scrub.

Geology? Oh, my, yes! The presence of the Cascades creates a barrier to moisture coming in off the Pacific; not only do the mountains catch a large proportion of that moisture, but air descending the eastern slope is, well, descending. It warms adiabatically, with the result that air masses moving into central Oregon are most often capable of holding more moisture than when they went over the pass. Which means they don't drop any more moisture. In this case, the mere presence of all that geology has a profound effect on the types of vegetation that can grow, compete, and reproduce in different parts of the east side.

As an aside, much of central and eastern Oregon is referred to as "High Desert," both colloquially and technically; it bears pointing out that strictly speaking, "deserts" receive 10 inches or less of precipitation per year. My understanding is that the Alvord Desert, on the east side of Steens Mountain, does meet this criterion, but little if any of the rest of Oregon does. More accurately, most of the High Desert is semi-arid grassland, but that just doesn't have the same ring, does it? So High Desert it is.

Not to rain on the parade, though, I think one of central Oregon's best-kept secrets is that there's much more water than I think most people realize... which means, in turn, more vegetation and wildlife than they might guess, as well. Yes, there are stretches that can seem barren (to the unaccustomed eye), and there are lots of glorious "dear gawd, look at all those nekkid rocks" vistas, but there's water, too, and lots of birds.

I had planned to spend the first night in the Chemult area, and had used the old Google machine to check that were indeed hotels in the little town. Oops. Without paying very close attention to where, exactly, said lodgings were, you know, located. There were a couple of ramshackle sorts of huts, members of the Bates Chain of Fine Accommodations, if you catch my drift.

So we put in an extra hour of driving to get to Klamath Falls.

As we rounded Modoc Point, we had a grand view of Upper Klamath Lake... ...and a short distance later, took advantage of a pull-out for a more lingering view.
Don't let all that sparse eastern Oregon water distract you from the fact that it's beginning to look a lot like basin and range. If I were asked to stick a tack onto a US map at the northwestern-most corner of that physiographic province, it's fun to imagine an enormous steel pillar suddenly splashing into existence somewhere out in that puddle.
Our diversion to K-Falls had some downsides and caused some later logistical problems, but also led to some fortuitous stops which we otherwise wouldn't have made. (Dana has already posted on one of those from the next day.) All in all, things worked out well; it was a good first day.

Volcanic Ramblings Part 4: The East Side Apron

The Oregon Cascades are conventionally divided into two N-S sections: the western Cascades, which start as low foothills on the eastern margin of the Willamette Valley, then rise to quite respectable heights before sloping down to the High Cascades. I know that sounds oxymoronic, but it's an accurate description. On route 20 in particular, one crosses two very well-defined passes. You may recall this diagram from my post on Salt Creek Falls:
The Western Cascades is older, ranging from roughly 35 Ma to 5 Ma. The combination of our wet PNW climate, the fragmentary nature of much of the rock, recent glaciation, with the lack of ongoing volcanism means that the Western Cascades have been deeply incised. Indeed, some of the canyons through the area are awesome, and the Western Cascades overall are far more precipitously rugged than the High Cascades- with the exception of some of the big stratovolcanic peaks.

The High Cascades, as implied above, are younger, from about 5 Ma to present. In a few areas, recent glaciation has cut deep canyons well into the High Cascades platform, but overall, the province is a surprisingly gentle swell, punctuated with a relative few peaks that rise another 5000 feet or so above the ~5000-foot pass levels.

The moniker I applied in the title, "the East Side Apron," is entirely my invention, and is not used in broader literature, as far as I know. However it does a good job of expressing my perception of descending eastward out of the mountains toward Central Oregon: a very smooth and steady decline. There are exceptions, of course, but by and large, the east flank is exceptionally gentle. It gets comparatively little precipitation, so erosion is subdued, glaciation was much more moderate than on the west side, and the prevailing winds are from the west, so tephra-rich eruptions regularly cover the landscape with inches to feet of ash and debris, smoothing it out.

One of the more recent large eruptions in Oregon, that of Mount Mazama, is easily recognized in many road cuts in the central part of the state; when coming down from Willamette Pass on route 58, I always point it out to my traveling companions, and if interest warrants, make a stop. The general area where it becomes too obvious to miss is near where the Crescent cut-off takes off to the east near Odell Butte.
Mazama ash and tephra has a distinct creamy-yellow color; its coarseness varies, becoming finer with distance from Crater Lake. Where roads have been cut into and through it, you can see that it has a consistent thickness in a given location, but that unlike a bed of sedimentary rock, it is not horizontal. It follows the shape of the landscape.
In fact, after bringing this odd layer to Dana's attention, it only took a couple of prompts, "Look at the way it's following the landscape," before she let fly with a squee and wildly started scanning for the first safe pull-out she could find.
(lens cap is ~52 mm) As she notes in her description of this stop, the dark cinders are from winter time road gravel, but there's no problem finding as many pieces of pumice as you want to carry away.
I ended up with maybe 7 or 8 of the little buggers; I wanted to stop later to get a couple of head-sized chunks off the roadside near Chemult, but that ended up not happening. Another time.
The best part of this stop? Dana's non-stop squeeing and exclamations.

Volcanic Ramblings Part 3: Salt Creek Falls

In Memoriam: Harold "Sharkey" Enlows

There's not too much of note to see on the drive down I-5 from the Corvallis exit to Route 58 just south of Eugene... at least little I'm not jaded to. So with an exception I'll tack on at the end, our first stop was at Salt Creek Falls. As the second tallest waterfall in Oregon, it's an enjoyable, lovely stop for anyone, even non-geotypes. I must say, Dana and Cujo359 got an earful of my griping about the $5 day-use fee for what used to be a nice, free roadside rest.

Dana has focused mostly on the glacial aspect of this spot in her post- and that is indeed an important part of the story- so I'll look more carefully at the bedrock geology. The Cascade Volcanic arc has an interesting evolutionary history. I have no idea if the pattern is unusual, but it youngs and narrows toward its eastern margin. In other words, when volcanism initiated about 35 mybp, following the docking of Siletzia (the Coast Range block), and subduction started outboard of that newly accreted terrane, it spread from the eastern side of the Willamette Valley to central Oregon. As time passed, though, the axis of active volcanism narrowed to what is now a fairly confined band along the eastern margin of what was originally a wide swath of activity. So the arc- at least in Oregon- can be divided into two portions: the Western (older) Cascades, and the High (younger) Cascades. The Western Cascades were more explosive overall, and produced a huge pile of pyroclastic rocks, volcanoclastic sediments and debris flows/lahars. They were also the ash source for the John Day formation in central to northeastern Oregon, famous for its preservation of Cenozoic mammals and other organisms.

According to a conceptual model developed by Ed Taylor, and apparently largely accepted on the basis of subsequent work by him, his students, and others, the origin of the modern Cascades began with the foundering of the ancestral "Plio-Cascades" 4-5 mybp into what is referred to as the "High Cascade Graben," as shown schematically above. The image that understandably comes to mind when one pictures these mountains are the big stratovolcanoes, but they are the exceptions, not the rule. Most of the High Cascade arc actually consists of a low ridge of basalt, andestic basalt, and basaltic andesite.

So what does all this have to do with Salt Creek Falls? When we stopped here with Sharkey, it was not for the pretty water feature, but because it was the boundary between the Western and High Cascades. The lower layer of rock, of Western Cascade affinity, is one I have not had an opportunity to look at closely, but judging from its fragmentary nature at a distance, I feel safe saying it's probably either lahar deposits or pyroclastic rocks of some kind- dark in color, so probably fairly mafic in composition. Overlying the fragmented rock is a thick intracanyon High Cascade mafic flow- Dana has found a source saying it's andesite, and I have no reason to say differently. I never could distinguish the mafic lavas without a petrological scope. So in a nutshell, we have a thick, competent, vertically-jointed rock overlying a soft, easily weathered and eroded rock.

This is a classic set-up for a waterfall.

Water erodes the softer rock and undercuts the overlying hard rock, which, because of its vertical jointing, slabs off to form a vertical face. While in most cases, erosion would incise and smooth the streambed, in this case, the physical arrangement of components acts to maintain a shear face. There are certainly other ways waterfalls can form, but I think of the "hard-over-soft" scenario as being the most common.

Well, isn't that sweet. Blooger has decided it controls the vertical and horizontal again. Sorry, I'm tired of fighting with this for now... maybe I can figure out how to fix it later.

Looking downstream, ~west, from the top of the falls.

This is perhaps not the best possible view to show it, but the landscape is pretty clearly the product of two distinct phases of erosion: a broad, glacially carved valley, followed by Holocene incision by Salt Creek.

The falls from the north rim...

...and from halfway down the trail.

Lovely columns.

Woot! Photo Shout-Out From NASA!

A photo I took on our recent Volcanic Ramble has received a complimentary treatment from Robert Simmon, along with a structural interpretation by Callan Bentley (@callanbentley ) And to make sure all involved parties get appropriate credit, that's Dana Hunter's hammer (currently on sabbatical with Bif and me), held by none other than the lovely @Dhunterauthor herself. Boo-Yah! Teamwork!

BTW, I've been repeatedly distracted from my efforts on Salt Creek Falls this afternoon, but I'm hoping to have that up before I go home.

Volcanic Ramblings Part 2: A Dedication

I'd like to start off the more methodical portion of this "Volcanic Ramblings" series with a heart-felt dedication to Harold "Sharkey" Enlows, who first showed me many of the stops we made on this trip on the 1984 Petrology series spring excursion. Enlows could be curt and abrasive, but in his way, he was a very caring Teacher. He wasn't affectionate, but he simply wouldn't accept less than what he believed a student was capable of. His nickname arose not from fear, but from the respect and fondness his students felt toward him.

One example: I was not the most responsible student in the history of studenting (I've always said, "I'm an excellent learner, but I'm a terrible student."), and frequently missed early morning classes. The petrology/petrography series lectures fell into that category. So when the test for metapet rolled around, and I was confronted, on the first page, with the question, "Describe the mono-mineralogical problem with respect to metamorphic rocks," I mentally shrugged and skipped it. Sharkey typically sat in his office and did other paperwork while classes took tests, and when we finished, we took our tests to him and dropped them off. He glanced up when I dropped mine off. I turned to go, but he brought me to a sharp stop with "Hold it, DeWitt!" I knew that tone. I turned, and he had his finger on the hole where an answer should have been. I muttered, "I think I must have missed that day," to which he responded, "You did. But you can figure this out. Take this (he shoved the paper back at me) and go sit down until you do."

I had it sussed even before I got back to my seat. If you have only one mineral phase in a nice clean metamorphic rock- like a quartzite or marble- it's nearly impossible to say anything quantitative about the T & P history it's been through. Metapet depends on finding how differing elemental components have been partitioned into differing mineral phases; only one phase, no partitioning. So within a couple minutes I was back in his office, waiting, embarrassed, while he made a great show of reading my answer, then flipping through the rest of the pages to make sure there were no other blanks. He rolled his eyes at me and said, "Good. You're sharp. Don't let lazy get in the way."

Word.

When I graduated, some years later, I made a point to visit most of my profs to explicitly thank them for the effort they'd put into my education. I do believe most of them were close to teary-eyed (I know I was); too few students make that small effort of their own. But I didn't make that happy trip to Sharkey's office. Why? Because unbeknownst to us undergrads, he had been diagnosed with and in treatment for cancer for the entire year we'd had him as a teacher. In summer of 1984, just a month or so after we finished his class, and less than two after he took us on what remains to this day one of the best field trips of my life, the disease took him. One of my biggest regrets is that I never had a chance to express my respect, thanks, and admiration to his face. He wasn't my "favorite" prof, but he's the one who made me work the hardest, and from whom I learned the most.

And that's no small compliment.

So for each of the stops we made on our Volcanic Ramblings that I saw first under Sharkey's tutelage, I'll just skip over the long-winded intro, but preface the post with a dignified "In Memoriam: Harold "Sharkey" Enlows." It feels like the least I owe him.

I was going to write up our first official stop, Salt Creek Falls, but it occurs to me I've forgotten to eat today, and I need to blow my nose and dry my eyes. Dana will have Salt Creek Falls covered for you in the near future. Here's a spur-of-the-moment photo I took when we stopped for gas out near I-5, on our way out of town, looking back over Corvallis to the iconic profile of Marys Peak.

Marys Peak, Oregon: a fore-arc uplift of seafloor basalt overprinted with oceanic plateau basalt, topped with a frosting of deep-water turbidites, then intruded and capped with a gabbroic sill.

Volcanic Ramblings Part I: Teaser Tweeting

I'm now back in my sleepy little home town of Corvallis, blissfully sipping coffee at my favorite coffee shop. Bif the kitteh was clearly traumatized by his 5-day abandonment; the person who was to feed and water him and give him a little attention and company didn't, and the back-up apparently didn't really do back up. His water was low and filthy, and it looked, from the amount of food spilled around, that the bowl was filled to the brim once, then forgotten. I don't know what the whole story is yet, so I'm keeping my temper on simmer. The good news is, as frantic and scared as he was when I got in last night, he calmed and quieted down as the evening went on, and seemed pretty relaxed this morning.

While I did have wifi most nights, what I didn't have was energy and time to say anything of substance regarding the day's sights and events. So starting day 2, I made my priority to get my photos downloaded to ye old electronical difference engine, and get a few "teasers-" photos I was pleased with- uploaded to Twitter, with a minimum of commentary and concern with geological utility. I figured those things were better addressed with blog posts, which simply were not going to happen. Between the difficulty of sleeping in unfamiliar beds in unfamiliar settings, and days that invariably ran longer than anticipated, I think it's fair to say all three of us spent the trip in a state of semi-exhaustion, and complete exhaustion by the time we retired to our respective rooms.

So herewith are the photos I posted from the road, more or less in the order we visited the sites, along with the associated Twitter comments I made when posting them. I'm not going to try to resize these to larger, but they should all get much bigger if you click on them or open links in new tabs with a right-click.

Booyah geotweeps! Tired, but great geo! Few pics: 1, Salt Creek Falls, yday

Volcanclastic seds, diatomite, coal, on Rt. 97 N of Klamath Falls, ~30 mi.

Pinnacles, Crater Lake NP

@Dhunterauthor in front of lahar deposit filling cut into volcaniclastic sed layers

Platy jointing 1; hammer middle bottom for scale.

Platy jointing 2, partway up Doherty grade. #1 in left middle of #2

Pisolitic texture in devitrified rhyolite (I was reminded later by @CGKings317 that the correct name for these structures is "spherulites," however, I'm not sure "pisolitic texture" would be incorrect in this context. Any geo-terminology nerds care to clarify?)

Filling in the happy little alluvial fans- Doherty Rim

One more pic before bed: Hart Mountain (on right) from near Adel, OR.

Summer Lake: a geologist was here (before us, I mean)

Ball & pillow structure in Table Rock tuff cone deposits.

Yaaaaaay! Correlation is fun! (Table Rock tuff cone deposits)

@callanbentley The rarely observed "splort structure." (Table Rock tuff cone)

Palagonite tuff at Fort Rock, OR

3 episodes of palagonite tuff accumulation, 2 of sloughing into blast crater, & 1 major episode of wave erosion.

Mahogany obsidian (looks like Glass Butte) in facade of hotel where staying tonight (Budget Inn, Bus. Rt. 97, Bend OR)

Parasitic cinder cones on NW flank of Newberry Volcano, from top of Lava Butte

A few final teaser photos from last day of volcanic rambling: 3 Sisters, Paulina Peak Pinnacles & Paulina Lake

Paulina Lake, Central Cinder Cone, East Lake and obsidian flow, ringed by Newberry Caldera

Contorted flow banding in Newberry Obsidian Flow (need to measure lens cap, but recollection is 52 mm)

Flow banded block broken off and re-entrained in more flow banded obsidian, Newberry Caldera, OR.

One more: Dee Wright Observtory, McKenzie Pass, OR: a most propitious place to observe volcanoes

Keep in mind, these are intended just to be quick and dirty updates, and to tantalize various geobloggers with hints of things to come. I will post the majority of these photos again with more detailed discussion and many additional shots from the same stops and areas. I shot 625 pictures on this trip, so the above, while including some of my favorites, are truly only a drop in the bucket. Also be sure to follow @Dhunterauthor (En Tequila Es Verdad), who was my impossibly generous sponsor, delightfully enthusiastic traveling companion, and increasingly, dear friend on this grueling but wondrous excursion. She probably took twice as many photos as I did. The third member of our company, Cujo359, blogs at Slobber and Spittle, and while not as enamored with things geological as Dana and I are, also helped underwrite my participation in this adventure, and showed enduring patience in the face of our lithic fixation. He has already posted a lovely picture of a rail trestle west of Oakridge OR, and will undoubtedly post further documentation of this trip in the days and weeks to come. Followup: Thanks to a commenter on that post, information on a large landslide has come to light, which Cujo359 has gone through and discussed in detail at the link. For example, mud/debris lines 50 feet up the tree trunks...

I make no promises regarding the regularity or frequency of posts in this series, but I'm looking forward to working through some first-hand experiences at long last. Stay tuned!