Ecosystem Notes from Quinault Rainforest
Introduction
I’ve spent the past few months wandering the Olympic Peninsula with my attention fixed mostly on rocks—tilted beds, breccias, sea stacks, and the stories they tell about deep time. But along the way I’ve been noticing the living world with the same quiet fascination. I’m not a biologist and I don’t pretend to be; I can’t name any of the plants I pass. What I can see is how each organism plays a role in the larger system, the way geology shapes life and life responds in turn. These are simply notes from a wanderer paying closer attention.
I’ll try to remember to label these environmental posts as NOTES to avoid any confusion, especially on my part. This first post arises from a short walk on a semi-muddy trail through the Quinault Rainforest, on the Olympic Peninsula. I won’t have much to say about the photos, and all identification will come from CoPilot (aka ChatGPT). I’m certain its identifications will be better than mine after hours of searching the internet.
Quinault Rainforest in Olympic National Park
Plate 1. That raging stream about 50 feet below me is one of hundreds draining this temperate rainforest, which gets about 12 feet of rain per year. Note the ferns, which are everywhere, even in the temperate forests of northern Virginia. Ferns must be the most common plant in cooler forests. I am in a narrow strand of Olympic National Park that has never been logged. This is primordial nature, viewed by a geologist, but I’ll do my best.
Plate 2. Map of the Olympic Peninsula showing the areas I reported on in previous posts. I’m going to be focusing on Site A today, with a few photos from D.
Plate 3. I haven’t seen this anywhere else I’ve lived, not even northern Virginia, but they occur everywhere here in Washington. Apparently this is a common occurrence in rainforests, where the ground is a dangerous place for seeds. I couldn’t identify the species in this photo, but this practice is very common for hemlock.
Plate 4. This pile of debris is a large log turning into compost and supplying nutrients to a variety of plants. The top of the photo shows the base of a young tree growing out of all this chaos. According to CoPilot and the Olympic National Park map, this area has never been logged, so I am in wonder of this pile of “forest garbage”. Is that sandy soil I see? Where did it come from? I don’t know.
Plate 5. If you look close in the exact center of this photo, you’ll see daylight on the other side of the base of this unidentified tree. It’s about six-feet in diameter and covered with an epiphyte community of mosses and liverworts. Those aren’t leaves or fronds, but communities that mimic ferns–for their own reasons.
Plate 6. Here’s an example of a Western Red Cedar that has grown into a mature tree after being nursed by a stump. I guess it will eventually absorb the rotting stump and grow to full height, but this is the largest I’ve seen so far in the region.
Plate 6. This miniature ecosystem caught my eye, but I had to turn to CoPilot to get an idea of what’s going on. As a tree trunk decays it goes through five stages: 1) moss; 2) liverworts; 3) fungi; 4) shrubs; and 5) young trees. This one seems to be in stages 1-4. I didn’t see any seedlings on it. The shrub is probably huckleberry and the mushrooms a bracket fungus, probably Trametes or Stereum.
Plate 7. I am fascinated by these nurse trees after seeing species of fig trees in Australia that devour living trees, like a giant fungus or alien. These are nursing on dead trees, however, so it isn’t as gross; but this one is now standing on its own legs after the original stump has begun to collapse.
Plate 8. This is the largest Spruce tree in the world. It’s 191 feet tall and about 1000 years old. It is growing in a swampy wet land at the inflowing stream to a glacial lake, Lake Quinault.
Plate 9. I thought this was toxic waste until CoPilot took a look at the photo: this is a mass of frog eggs (probably northern red-legged frog). There were several more at the shallow, marshy wetland where a stream fed Lake Quinault. The water is so clear you can see the bottom, which is only a couple of feet down.
Kalaloch Beach in Olympic National Park
Plate 10. This one was a doozy. These objects are one-two inches long, thin, translucent, and oval in general shape. At first, CoPilot suggested insect wings (until I told it the size), then gull secondary feathers (until I said, “no way”), then settled on small fish cranial bones–e.g. the opercula, the bone that covers the gill. I asked for references, but it supplied me with titles and no links (how did it find them?). I spent longer on this photo than I wanted to. I don’t fault CoPilot for its ambiguous response because I found nothing when I looked very specifically. This phenomenon is either so common that no one bothers mentioning it, or infrequently observed that no serious beachcombers have stumbled across it. I’m going to have to agree (for now) with CoPilot that these are small bones from a school of fish that was decimated by either predation, coastal fishing, or disease and only these translucent cranial bones survived by floating, until waves concentrated them on this beach. This is the only beach where I saw them. I guess there are no easy answers to some questions–unless someone who reads this is a marine biologist.
Cape Flattery
I reported on this amazing location in a previous post. You can scan that post to get an idea of where these photos were taken.
Plate 11. I don’t know if this living (it looked healthy to me) tree was stressed or not, but CoPilot thinks these are perennial bracket fungi, which favor environmentally stressed conifers. There were only a few on this tree. I noticed that this forest didn’t show nearly as many signs of decay as Quinault Rainforest, despite its exposed location.
Plate 12. I had to throw this photo in because the root growing out of the tree(s) on the left looks like a dog that got its head caught in a hole, and died there. Its limbs of limp. Overactive imagination, I know. Nevertheless, this is a bizarre image because the dog is lying on top of a mound of soil. I’d bet there was a stump there that has decayed because the trees visible in this image are both composed of multiple trunks. A large tree died here (like the dog) and these are its adopted offspring. I would add that Cape Flatters, which is part of the Makah Reservation, has never been commercially logged. This is old-growth forest and this is a naturally occurring phenomenon.
Summary
Moisture drives everything on the Olympic Peninsula, soaking old volcanic and sedimentary foundations until the forest grows straight out of its own decay. Fallen logs become elevated nurseries, their wood breaking down under fungi and mosses until they’re more sponge than tree. Hemlock, cedar, and huckleberry take root on these platforms, sending roots around stumps and into the thin soils draped over ancient bedrock. Even the beaches tell the same story: waves sorting bones, shells, and driftwood carved from headlands shaped by tectonics and storms. It’s an ecosystem built on slow collapse and constant renewal.
Acknowledgment
I am experimenting with using CoPilot (aka ChatGPT) to help as I pursue my growing interest in ecosystems. I have been up front about where it contributed. It has been a great help, as well as an inspiration; if not for CoPilot, I wouldn’t have had the time of inclination to add these ecosystem NOTES to Rocks and (no) Roads. In fact, I’m tired of this entire series of posts, for which I get no compensation other than sharing my observations of the world. As a final note, CoPilot wrote the Summary and I stand by it.
Now I have to think about more than just rocks…
Cape Flattery: Conglomerates at the End of the World
Figure 1. I ran out of road and land, ending up at Cape Flattery on the Makah Reservation. This is Location D in Fig. 2. A half-mile hike down a boardwalk took me to the end of the world, where the cliffs are about 80 feet above sea level. This photo is looking northward towards Vancouver Island, Canada, in the distance. Wave action has cut a wave terrace, a seen in the center of the image, and a series of sea caves.
Figure 2. Today’s post takes us to Site D, which is shown in a geologic map from Rock D in the inset map. The rocks are a mixture of sandstone and conglomerate of Eocene age (56-34 Ma). This is the same time that the lower Cascades were being created east of Puget Sound. Note the large number of faults (thin lines) shown in the inset map. Many of these are strike-slip faults with motion of the opposing crustal block to the left, which would explain why the sedimentary layers in seen in Fig. 1 are almost horizontal, dipping slightly towards the sea.
Figure 3. The sea stacks seen further south have been replaced with rocky islands like Tatoosh Island, which has a light house. Pacific Ocean seafloor (Juan de Fuca tectonic plate) is being actively subducted along the Washington-Oregon coast at about 2 inches/year, but the plate tectonic geometry is complex in this area. This could partly explain the large number of faults seen in Fig. 2 as well as the high elevation of bedrock. Maybe.
Figure 4. This photo was taken looking down towards the wave-terrace on the south side of the lookout point. For scale, the largest boulders are a couple of feet long, based on exposures at the surface of the trail. This is a textbook tectonic breccia. However, note that most of the rock fragments are rounded, so they have been transported some distance before reaching their final resting place. Some of the layers are relatively uniform with a few large boulders whereas others resemble the cobblestones we saw at Ruby Beach. Each bed might represent a single depositional event (like a landslide) or accumulation over years. These are marine rocks, deposited on a submarine fan, probably as turbidity flows. The process that created them is occurring now a few miles offshore, where the rocky outcrops we saw are eroding and supplying large and small fragments to a steep continental shelf.
Figure 5. This image looks like run-of-the-mill gravel like you see on pathways and drives, but it is Eocene rock, and I mean solid rock (Note the large, gray piece protruding from the cliff in Fig. 4). This angular slab is about a foot in length. There is no Pleistocene glacial till in this area, even if the ground looks the same. This is a picture frozen in time, where an angular piece of what looks like sandstone, but could be andesite, slid downslope along with smaller fragments.
Summary.
This is the last of my geology posts from a weekend excursion along a hundred-mile stretch of the Washington coast. This is a high wave-energy coast with a tidal range of about 10 feet, the beaches covered with sand and cobbles. Sea stacks protrude from the beach, culminating in cliffs made of 50 Ma conglomerates. Beneath our feet, ocean crust was being subducted at several inches per year, feeding a system of magma chambers that are actively venting through volcanoes like Mt. Saint Helens, Rainier, and Mt. Baker. Rainfall drops along this coast at up to 12 feet per year, feeding streams that carry immense quantities of sediment into the trench created by the subducting ocean crust.
Geology doesn’t get any realer than this…
Tectonic Breccia at Ruby Beach
Figure 1. Ruby Beach is located about 10 miles north of Kalaloch Beach (Point C in Fig. 2), but the coastal morphology has changed substantially. This photo was taken at sunrise during low tide, exposing many outcrops of basement rock, which is the same unnamed sandy rock formation we saw before, but its composition has changed.
Figure 2. Today’s post describes the coastal geology at Site C. I’ve already discussed the Quinault Rainforest and Kalaloch Beach. I will focus on what is different from the previous post. The inset geologic map from Rock D will be referred to below.
Figure 3. Basement rock of general Tertiary age (66.5-2.4 Ma) is more exposed here although it is overlain by Pleistocene glacial sediments. This photo shows a rocky island that can be reached at low tide, and a promontory. The beach is composed of rounded cobbles in a matrix of sand, silt, and some clay. The finer sediments are restricted to the lower swash zone (Fig. 1).
Figure 4. This is a sea stack, a standalone rock pillar. The beach is a thin veneer spread across a rocky basement that is more irregular than we saw at Kalaloch Beach, where the outcrops resembled a wave-cut platform more than we see here. The first thing that occurs to me is that this area hasn’t been exposed to the erosive power of waves for as long an interval. Maybe. Let’s take a look at the inset map of Fig. 2. The black lines represent geologic faults, where rocks have been displaced by tectonic activity. Note that the stretch of coast we’re concerned with is bounded by faults perpendicular to the coast. Furthermore, there is another fault separating Sites B and C. I should take a moment to point out the relationship between faults and river valleys: faults create weak zones within the crust, which are exploited by erosional forces like water and glaciers. Thus we see valleys at both B and C; however, the intervening fault is part of a complex fault system that appears to have led to less surface erosion. Faults cannot be directly dated, only indirectly by the age of the rocks they displace, and in this case those rocks are themselves difficult to date. Thus, it is possible that vertical movement, even a few hundred yards, could have made this beach more irregular than Kalaloch Beach only a few miles to the south–on the other side of a fault. Plausible, but don’t bet your retirement on my hypothesis.
Figure 5. Back to the rocks. This photo puzzled me because I’m not an experienced field geologist, despite my regular posts; however, CoPilot came to the only plausible conclusion: the primary material here is a breccia/graywacke; the smoother material is calcite filling fractures that occurred during faulting (see Fig. 2 inset). We must ALWAYS remember that a sedimentary rock’s history isn’t confined to deposition; a lot happens during burial to many miles and subsequent exhumation and deformation.
Figure 6. This photo shows a typical graywacke texture with layering, as you might expect with episodic deposition of event beds (e.g. turbidites on a submarine fan); but the upper part of the image is similar to Fig. 6. I asked CoPilot about the source of so much Calcium and I agree with its answer: Some of the Calcium came from marine invertebrates living in the area, but the bulk arrived later, when the sediments were buried deep (several miles) within the accretionary wedge where Calcium is released from minerals like feldspar. It’s really hot down there and the pressure is INTENSE.
Summary.
Not only was Ruby Beach a beautiful area on a cool winter/spring morning, it gave us more insight into the complex life of the earth’s crust. These rocks were probably deposited as poorly sorted graywacke on a steep continental margin overwhelmed by sediment eroded from the rising Cascades (more than likely the Eocene, 56-34 Ma). They were buried for a few million years, before being scraped off the subducting oceanic crust and filled with hot fluids that originated from deeper within the accretionary prism. They were never so humiliated that they became melanges but it was a pretty rough ride, even for a rock.
To put this all in perspective, dinosaurs had just gone extinct (~65 Ma) when all hell broke loose and the Cascades Subduction Zone became very active about ten-million years later; the earth became hot as hell, mammals and birds were beginning to get their legs and wings. While the ecosystem changed dramatically, these rocks were being ground up and spit out by the earth because they were stuck on the end of its tongue. We hominids didn’t come along until these rocks were exposed to the vagaries of the weather and had eroded for a VERY long time.
Try not to laugh at the punch line: Our entire history is contained in the Pleistocene glacial sediments overlying these fairly young sediments.
It boggles the mind…
Coastal Geology of Kalaloch Beach
This report is the geology supplement to my general post about the Olympic Peninsula. It focuses on the geology of the beaches because, to be honest, Quinault Rainforest was impenetrable, physically and geologically, without massive logistical planning and support. What I found was more than I expected.
Figure 1. Photo looking north along Beach 4 at Site B in Fig. 2. The tidal range is about 10 feet here and the primary sediment consists of sand with a substantial mud component. The rocks seen in this image are bedrock that protrudes above the veneer of beach sediment. The cliffs to the right comprise glacial till that is less than 2.4 my old (Ma hereafter) deposited by glaciers during the Quaternary geological period. This photo was taken near low tide. The dark color of the beach surface is caused by the relatively large clay component (i.e. mud).
Figure 2. Location map of today’s field area, which will focus on Site B.
Figure 3. Schematic of the Cascadia Subduction Zone as it appears today. The Coast Range, which includes the Olympic Mountains, consists of sediments and volcanics that have been scraped off the subducting ocean crust. The white arrows at the front of the image don’t reflect the actual geometry of these sedimentary rocks. We’ll get to that in a minute. Today’s post will focus on these sediments and discuss their original depositional environment during the Tertiary period (~65.5-2.4 Ma), as well as evidence for structural deformation.
Figure 4. This photo has been marked-up to highlight what might not be obvious to a non-geologist. First, older sedimentary rocks have been tilted to a high angle (dark blue bedding plane line) by faulting, as suggested in Fig. 3, and exposed to erosion at the surface. This erosional surface is shown by the yellow line. These Tertiary sediments were buried several miles beneath the ocean surface where the grains were cemented by heat and pressure. We don’t know exactly when this occurred or how long this process took, but they were later overlain by younger glacial sediments during the Pleistocene epoch (2.4 Ma to present). The age of sedimentary rocks can’t be pinned down unless they contain material datable by radiometric methods or, more qualitatively, by the fossils they contain. Sandy sediments don’t contain fossils very often and I didn’t find any radiometric ages in either Rock D or the USGS geologic map, so I guess the Tertiary date is the best we can do for now.
Figure 5. Close-up photo of the contact between the Tertiary rocks and the glacial till. Note that the cobbles aren’t falling out of the fine matrix sand and clay; this is because these young (>2.4 Ma) conglomerates have been partially cemented and, in fact, they were stuck to the older rocks below. This photo tells us a lot: 1) the older rocks were tilted at depth (maybe a mile or more) and then pushed upward as suggested in Fig. 3 until they were exposed to the atmosphere; 2) in a very short time they were covered by cobbles (~2 inches or less) that had already been rounded in a river, which takes several miles of transport; 3) the type of sediment varied rapidly, from coarse sand to cobbles, probably within decades if not years, due in part to periodic changes in surface drainage (e.g. the advance and retreat of glaciers); 4) this is a good example of the principle of Uniformitarianism–the present is the key to the past: we see similar processes occurring today along the many streams and rivers draining the Olympic Mountains. But what about those pesky Tertiary sandstones?
Figure 6. This photo of the Tertiary sedimentary rocks reveals packets of thin-bedded fine sandstone with intercalated dark layers of (presumably) mud. I didn’t see any cross-bedding, which would indicate deposition in a river or nearshore dominated by waves or currents. What is obvious that this ancient (~50-2 Ma) shoreline was receiving sediment from a distant source, probably the volcanic highlands of the modern Cascades (see Fig. 3). Let’s take a closer look at one of those wavy layers.
Figure 7. Close-up image of a thin layer (about 3 inches), showing what is called Flasier bedding. This is found in modern environments where high-energy (e.g. waves and tides) periods are interrupted by quiet times during which fine sediment can be deposited between ripples. It is indicative of a shallow marine environment.
Figure 8. These holes were evident throughout the exposure. They are problematic and probably originated in several ways; however, one plausible explanation is that soft-bodied animals like worms burrowed in the sediments and their burrows filled with sediment with a different composition (e.g. fecal pellets). These channels then preferentially eroded when subjected to the harsh nearshore environment in which they are found. The presence of such holes at the unconformity (see Fig. 5) proves that they predate deposition of the overlying glacial till. Unfortunately, such trace fossils don’t tell us anything about geologic age, only that this seashore was teeming with life.
Figure 9. I stopped at another accessible beach a couple of miles south, but still indicated as Site B in Fig. 2, where the rocks were sandstone but with very little clay. The beds seen in this photo were thick (1-3 feet). They were not deposited in a high-energy, environment like those we saw before; they were probably deposited on the shoreface below fair-weather wave base–possibly part of a nearshore bar or barrier island. After deposition and burial, they were tilted less steeply than those seen further north (Fig. 6). The unconformity is seen in the upper part of this image, but it doesn’t seem to have as many rounded cobbles as before (Fig. 5). I have no way of knowing the relative age of these two exposures; this Tertiary rock unit is approximately 3000 feet thick and represents millions of years. All we can say for certain is that this shoreline wasn’t that different from what we observe today. Uniformitarianism in action.
Figure 10. This exposed outcrop within the tidal zone reveals what are probably concretions of iron oxides, formed during early diagenesis. They superficially resemble fossils, but that is not the case. As the sediment was squeezed during burial, incompatible elements like iron formed irregular blobs in an otherwise uniform quartz sand matrix.
Summary
This coastline was part of the Cascadia subduction zone during most of the Tertiary period. Sediment, including a lot of sand, was eroded from rocks being uplifted further inland where volcanism was active, especially during the Eocene (55-35 Ma). Beaches like those we see toady were common, as well as the various depositional environments found along the Olympic peninsula, including fluvial and submarine fans, beaches, and cliffs. But no glacial sediment.
These sediments were buried as more material was removed from the rising orogenic belt, which included granitic rocks with lots of quartz. Eventually they were caught by the complex trench uplift (see Fig. 3) and scraped onto the edge of N. America. This involved faulting primarily, suggesting this was a fairly shallow process (folds occur at depth where rocks are ductile). The tilted rocks were eroded for millions of years; then, about 2.4 Ma glaciers (nothing to do with subduction) covered the region and deposited all kind of sediment: rivers, lakes, undifferentiated till, moraines, etc.
Just as the East Coast of America has been a passive margin for more than 200 my, the West Coast has been a convergent margin. Instead of being steadily worn away by wind and water, these rocks are rising out of the sea at about 2 inches per year. And what a ride it is…
The Olympic Peninsula: Quinault Rainforest to Cape Flattery
This is the first in what I hope will become a regular series of blogs from my travels around the Pacific Northwest (PNW) as well as trips throughout the world. This series accompanies my main blog, Rocks and (no) Roads, which reports on the geology of various places to which I travel. You could see I’m expanding my horizons; in addition to posting about general sights in this post, I will also be including environmental and ecological observations that are of interest to me. My background is in geology, but I’ve become aware of a lot more since moving to the PNW. So this is a learning experience, thanks in large part to the availability of expert assistance from CoPilot, Microsoft’s version of ChatGPT. I’ll be turning to it to identify plants and evidence of animal activity in future posts.
This is the base map I’ll be using in many of my posts from the PNW. The star indicates my base in Tacoma. Today’s post describes a two-day trip to circumnavigate the Olympic Peninsula. Although this area is the wettest in the contiguous United States, with annual rainfall up to twelve-feet, it was clear for the duration of my visit. The labeled areas indicate where the photos described below were taken.
Location A: Quinault Rainforest. Photographs can’t do justice to the experience of being surrounded by a temperate rainforest. There are many trails of different lengths, but I followed a shorter one (about one mile) that followed Willaby Creek for a while before turning into the depths of the forest. This image shows the creek rushing by about 50 feet below the trail as it races to the south shore of Lake Quinault.
Location A: Quinault Rainforest. This rotted log is about six-feet in diameter. It is representative of the ongoing decay and rebirth of the forest. I’ll talk more about that in another post. Note the ferns growing out of the decaying wood.
Location A: Quinault Rainforest. There are at least half-a-dozen species of giant evergreen trees in the rainforest, and I can’t identify any of them; but CoPilot suggests it might be a Coast Redwood, part of a local population found in this area. This example is typical in an area known for its “Champion Trees”. We’ll get to that in the next photo.
Location A. Quinault Rainforest. This is the world’s largest Spruce tree. It is 191 feet tall and about 1000 years old. It is one of the six champion trees located in Quinault Valley. The other champion trees are: the world’s largest Western Red Cedar, Douglas Fir, and Mountain Hemlock; and the largest Yellow Cedar and Western Hemlock in the U.S. This tree is growing in a wetland area at the NE end of Lake Quinault.
Halfway between Sites A and B. During my day-trips around the area, I’ve noticed a what appears to be a regional interest in post-industrial art, including but not limited to large concrete facilities that have been left to decay in place, as well as small sculptures and other curiosities scattered throughout the cities and forests. I don’t know if this is intentional or not: the roof of the information board collapsed (no doubt because of 12 feet of rain per year) and was set aside, possibly as a monument to nature?–or evidence of the poor funding and mismanagement of the National Park Service.
Location B: Kalaloch Lodge. This is the view from the deck of the lodge where I spent the night. Kalaloch Creek meanders as it approaches the coast and enters the Pacific Ocean here. An impenetrable pile of driftwood (actually logs and entire trees) has collected on a sand spit deposited on bedrock.
Location B: Beach 4 at Kalaloch. Steep bluffs of glacial till front a wide beach with many exposures of rock, which I’ll discuss in my next post.
Location C: Ruby Beach. This was the last beach before US 101 turned inland for ten miles. I took a video because a series of photos can’t possibly convey the beauty of this location as the sun was rising. Note all the rocks protruding from the water at low tide. The rocks are rising from the earth as we make our way north.
Location C. This selfie demonstrates how chilly it was, with the temperature below 40F. Rock formations like this are called stacks; they are erosional outliers as the coast recedes over millions of years, pounded day and night by rocks carried by waves; and tides that exceed nine feet–twice a day! You have to time your visit accordingly or all you’ll see is water.
Location D: Point Flattery. This is the extreme tip of the contiguous United States. The bedrock we saw further south, at Ruby Beach, now forms wave-cut cliffs that tower 40-80 feet above the waves. The top of the bluffs is 330 feet above sea level. The view from the catwalks is breathtaking. Vancouver Island, BC, is visible in the background, with peaks around 6000 feet.
More PNW Humor. All of the toilets we saw along the coast were constructed over septic tanks, with warnings about what to put in them. Someone with a sense of humor modified just one word of the official message…
If you get the chance, I strongly recommend visiting Olympic National Park, but you’re going to want to spend a week unless you live nearby in the PNW.
Gravel Beaches on Vashon Island
This photo of the gravel/mud beach at Fern Cove Nature Preserve reveals a marine delta, fed by Shinglemill Creek. Unlike the mud/sand delta we saw at Dash Point, the sediment here is dominated by rounded gravel and small boulders. Mud, sand and silt form the matrix. All of this material is available from the glacial till that comprises Vashon Island.
The inset map (right) shows the two sites I visited today. Fern Cove is located near the northern tip of Vashon Island whereas Maury Island Marine Park occupies the SE side of an island that is connected to Vashon by a fill zone about 200 yards across (which is eroding away as I type).
Fern Cove Nature Preserve
Vashon Island was logged out, so the beautiful evergreen forests that cover most of the island are all second growth. The state is trying to restore the original habitat, and Fern Cove is a good example; they don’t allow dogs!
I’ve noticed that people in the Pacific Northwest (PNW) appreciate industrial art of a practical nature. I found an example here, in a threatened habitat that is actively being restored. I guess this old truck body isn’t hurting anything; I’ve also noticed that communities in the PNW don’t waste money on unnecessary actions.
This photo shows how the gravel is localized within the delta, forming low nearshore gravel bars. The intervening areas are muddier than I found at Dash Point.
These gravel bars do more than concentrate larger rock fragments. Acorn barnacles encrust the larger ones, which are several inches in diameter. The tidal range is about 7 feet here and the beach is inundated twice daily, so I think these are living. I’ve seen barnacles on large boulders before, but I didn’t know they grew on stones. I guess the wave energy isn’t high enough to disturb them over a life cycle; their larvae must hang around after a storm and find a new rock to inhabit.
On all the beaches I’ve reported on for Rocks and (no) Roads, I’ve never seen this before. This is an active feeding area for sea birds. These are mussels, which the birds grab from a nearby mussel colony on the shallow delta front and drop on exposed gravel during low tide. The shells break open and the birds feast, leaving their dirty dishes behind.
This Western skunk cabbage is just emerging from the wetland surrounding Shinglemill Creek. It will grow leaves up to two feet long, but it makes a beautiful display in the unseasonably warm late winter we’re having in the PNW.
Maury Island Marine Park
On the opposite side of Vashon Island, I visited a gravel quarry that operated for about seventy five years, before being purchased by the state as a park. This is another example of letting nature recover without interference.
This photo looks SSE towards Dash Point. Commencement Bay and Tacoma are visible in the background; a little sunlight is shining on the bay. The cliff has been quarried for 75 years, so the 400-foot vertical face is now a steep incline with a trail that utilizes many switchbacks to reach the shoreline. Let’s see what I found…
There is no mud or sand visible on this beach. I thought that might be a side-effect of so much gravel quarrying, so I walked beyond the limit of the quarry; the substrate didn’t change, but there must be lingering effects after so many decades of preferential sand removal.
After what I saw at Fern Cove, I thought I was prepared for whatever I might find; but I never expected to see clam shells with the hinge lineament intact; this shell even closed after the bird (e.g. gull or crow) has eaten the soft tissue. The shell actually snapped shut after the animal was eaten. Amazing!
This spectacle gives driftwood a whole new meaning. Someone even built a crude shelter in the background from the logs that have collected over the years. There are a lot of trees in the PNW and many of them fall into Puget Sound, ending up all over the place. This looks like what coastal geologists might call a “hot spot”, a location where waves converge during storms.
After a hot climb, even in 45F temperatures, I made it back to the top of the cliff. This area was a barren wasteland in 1975, when the state took over; park authorities and volunteers have worked tirelessly to not only allow recovery, but to keep out invasive species. I think they’re doing a pretty good job.
Summary and Acknowledgments
I learned more biology on this day trip than in my entire life. For example, sea birds eat mussels on muddy beaches and clams on cobblestone ones. They carry the hard shells in the air and drop them on rocks, breaking them open to reveal the animal hiding within. Apparently I arrived at these two beaches just after lunch, when the tide hadn’t cleaned up the dishes yet.
I’m going to pay more attention to fauna and flora in my future posts.
I don’t know anything about biology, so all plants and animals identified in this post came from CoPilot (AKA ChatGPT). I didn’t check their identifications because it wasn’t worth the hours that would have required. This is not a research paper. I’m just going out into the world and observing through my dirty, discolored glasses.
But now I can see living things…
Active Delta Accretion at Dash Point State Park
INTRODUCTION
Puget Sound is a complex water body with many channels and bays, all of them within a couple of hours drive from my home in Tacoma. I haven’t posted much about this because I’ve been overwhelmed by so many active sedimentological processes that are neither marine nor fluvial. But I had to say something about what we discovered on this short trip, less than 30 minutes from our house. Because of the bluffs (~300 feet) surrounding Puget Sound, streams draining into the various inlets and bays are short and relatively steep. There are exceptions of course, such as the Nisqually River, which flows from Mt. Rainier to the southern end of Puget Sound; however, short streams are very common although many of them have been incorporated into municipal storm drainage systems. Today, we found one that was in an almost natural state.
Figure 1. This photo, looking landward from Dash Point beach, says it all: A small stream enters between the two bluffs, each about 200 feet in height, and dumps copious amounts of sand, silt and clay onto a mesotidal shoreline (the tidal range is about 7 feet), where the volume of sediment input overwhelms the nearshore wave and tidal regime to create an expanding delta.
Figure 2. (A) Regional map showing the complex, glacially sculpted, morphology of Puget Sound. The star is approximately where my house is. (B) Google Earth image from about 7000 feet showing Dash Point and the extensive delta being constructed by sediment delivered by a small stream.
Figure 3. The small stream feeding the delta has been confined to a stone-lined channel. This is the entire inflow. The water looks pretty clear, but appearances can be deceiving in the context of sediment transport. This is a bedload-dominated stream, which means that it is mostly transporting sand and silt, and minimal clay particles. The entire area surrounding Puget Sound is constructed of glacial till, which is mostly gravel and sand. A closer examination will confirm this inference.
Figure 4. This is the delta seen in Fig. 2B during an ebbing tide that is near its minimum. The expanse of the delta, at approximately the same tidal height, is seen here at ground level, revealing tidal channels and swales; but the surface is sand and silt with minimal clay restricted to the swales, like those seen in the middle of this photo.
Figure 5. The flattened sea grass serves as a current indicator that perfectly matches the ripple orientation. Note that the tops of the ripples are flattened by the high velocity of the ebbing tide. Waves weren’t very large on this particular day.
Figure 6. Sand bars are constantly being created and destroyed at the fringe of the delta, probably in seasonal cycles. I don’t know where a late February date fits into this cycle. Perhaps I’ll need to return in the summer.
Figure 7. The delta was less symmetric on this February day than the undated image in Fig. 2B. This image looks to the west. It reveals multiple shore-perpendicular sand bars, until the delta is interrupted by shoreline development. Nothing like this was present on the eastern side of the delta on this day. The sediment supplied by the stream in Fig. 3 is being transported westward in this shallow water, but not by waves like we saw on this day, which are perpendicular to the shore.
SUMMARY
Dash Point beach provided a great opportunity to study nearshore sedimentology. Just look at those ripples in Fig. 7! Despite being created and destroyed twice a day, we find rocks preserving similar ripples throughout geologic time.
With so much gravel in the Puget Sound area eroded from the glacial till (gravel and sand), it was exciting to see finer grained sedimentation occurring in real time. Gravel beaches are uncommon in the geologic record whereas rippled, sandy beaches are very common; after all, the previous source of this sand and silt was a glacial till, itself the product of erosion by ice and fluvial transport during the previous twenty-thousand years.
Material is recycled by our tectonically active planet.
Earth abides…
Snoqualmie Falls: Eocene Volcanism in the Cascades Subduction Zone
INTRODUCTION.
Figure 1. (A) Snoqualmie Falls is less than an hour from Tacoma, in the foothills of the Cascades Range of volcanic mountains. (B) The geologic map doesn’t show much besides glacial till, except around the falls (circled). I recently discovered that the Cascades is one of the youngest mountain ranges in the world, and it includes many active volcanoes that are part of the Pacific “Ring of Fire.” Most of the volcanic rocks were erupted from fissures and small volcanoes during the Eocene epoch (56-34 my ago). The active volcanoes (e.g., Mt St Helens and Mt Rainier) are less than a million years old, reflecting renewed magmatism at depth.
Observations
Figure 2. The 270 foot drop over Snoqualmie falls encouraged a private consortium to construct the world’s first subterranean hydroelectric power plant. The turbine outflow is visible at the bottom-center of this image. Note the massive wall of volcanics in the center of the photo. The exact origin of the falls is unknown because there are no major faults in the area, although the entire region is cross-cut by faults. The default narrative is a combination of glacial scour and natural variability in the rock composition and thus strength. For example, Niagara Falls was also formed during the last ice age along a natural escarpment, but the rocks comprise hard dolomite over soft shale; this combination led to undercutting and continuous upstream erosion at ~1 foot/year. All of the rocks at Snoqualmie falls are andesitic; however, note that the cliff ends to the right of the photo and a slope emerges. This could be a clue…
Figure 3. The riverbank several hundred yards downstream from the falls reveals a rock unit comprising large boulders in a matrix that erodes to form sand and mud.
Figure 4. A close-up of the downstream bank reveals boulders several feet in diameter protruding from the cliff face. As the softer matrix material erodes, these blocks fall into the river. These are volcanic bombs–partially molten lava that solidifies in flight before landing far from the vent; volcanic bombs up to 20 feet in diameter have been ejected 2000 feet from the vent in volcanoes in Japan. Because they are soft, these ejecta become smooth during their flight and are sometimes flattened when they land. Consequently they can look like rounded boulders and cause confusion when found in a river. The giveaway is the matrix in which they are embedded. However, the story is more complicated than that…
Figure 5. A boulder of volcaniclastic rock exposed in the river channel, rounded by collisions with other rocks. This sample is six-feet long. Note the mixture of tephra of different sizes and shapes. Each fragment was semi-molten when it was ejected from the vent; of course, it landed in ash rather than on hard ground. However…this sample comprises a matrix that is solid, not crumbly like the cliff base seen in Fig. 3; the only explanation I can think of is that the matrix varied substantially over time and space. In other words, this block represents an eruption of extremely hot ash, which formed a welded tuff (aka ignimbrite), encasing the tephra in stone immediately after eruption. The friable matrix in Fig. 4 wasn’t as hot; it is even possible (albeit unlikely) that this block was itself ejected from a younger eruption and became a volcanic bomb. I’m not putting any money on that; my point is that volcanic eruptions are very dynamic, and the rocks we see today represent millions of years of magma chamber depressurization.
Figure 6. This eight-foot boulder contains fine layering in its lower half. This suggests that the tephra landed in a layer of ash that was so hot it became a welded tuff, even as eruptions continued intermittently. This block is NOT a volcanic bomb (despite my speculation in Fig. 5); it is a sample of the volcanic debris erupted from a vent (including volcanic bombs), which was subsequently eroded from somewhere within the local area, representing an eruption so hot it created an ignimbrite. This sample (as well as Fig. 5) thus reflects eruption and initial deposition, followed by erosion in a stream–giving them a rounded appearance similar to that of the tephra they contain; thus the term volcaniclastics.
Figure 7. This is where this field trip got interesting. (A) This rounded boulder (4 feet across) doesn’t look like the volcanic rocks in Figs. 5 and 6. It contains no tephra or lamination. What’s going on? (B) A close-up photo reveals this to be an intrusive rock; individual mineral grains are visible, giving it a stippled appearance. It isn’t as coarse-grained as a classic granite with large crystals visible to the unaided eye; however, it isn’t extrusive either (microscopic grain size). This rock formed within a shallow magma chamber (possibly a dike or sill) in which the molten magma cooled faster than a deeply buried granite, but slower than an extrusive rock. This is common within volcanic terrains in which fresh magma is often injected into pre-existing layers of extrusive rocks. This sample is relatively fresh (i.e., no biological surface coverings) and thus its composition can be guesstimated: the whitish areas are feldspar (albite and plagioclase) that contains sodium and calcium, but not potassium; they comprise approximately half of the minerals; the darker grains are (probably) hornblende and biotite; a suggestion of gray implies some quartz. The relatively low quartz content suggests this is diorite. Diorite is the intrusive equivalent of andesite; it follows that the thickness of volcanic rocks visible in Fig. 2 is andesite, which is common in subduction zones. The bottom line is that this sample is NEITHER a volcanic bomb nor a block of the tephritic, extrusive rock seen in Figs. 3 and 4. It was probably emplaced within layers of older volcanics and later eroded, eventually falling into the river, where it was rounded by collisions with other boulders.
SUMMARY.
Figure 8. Snoqualmie falls is located at the northern end (top) of this schematic, within the second belt of mountains (green). The history of subduction along the Pacific Northwest (PNW) is uncertain because of intermittent subduction and crustal thickening. When Pangea split along what is now the mid-Atlantic ridge system about 200 my ago, the North American plate began a complex history of either riding over the Juan de Fuca oceanic plate or colliding with various islands and micro-continents that were in the way. By these disparate accretionary mechanisms, the west coast of N. America propagated westward hundreds of miles, at least from Montana. Jumping ahead to 50 my ago, a new round of subduction began, characterized by multiple vents, fractures, and volcanoes; these produced the older rocks of the Cascades. The Columbia plateau basalts were erupted about 15 my ago–Act II in this ongoing geological opera; the third act (using a simple theatrical model) was the appearance of multiple volcanoes fed by localized magmatic chambers in the last million years. This geological opera is complicated by at least two distinct events: (1) the San Andreas transform fault and associated strike-slip faults from Mexico to Canada, which together transport crustal blocks to the NW (i.e. Alaska); and (2) the anomalous mantle plume associated with the Yellowstone caldera.
Unlike the ancestral Appalachian mountains, whose geological history must be inferred from fragmentary and ambiguous data, the PNW geo-opera is being performed before our eyes.
Think about it–Mt St Helens wasn’t an outlier…anything can happen in the PNW…
Quaternary Geology on Mt. Rainier
Figure 1. View of Mt Rainier from the west. At 14410 feet, it is the most prominent peak in the contiguous United States. It has 28 glaciers, with the largest total surface area in the lower states–35 square miles. Mt Rainier is a stratovolcano, composed of andesitic lava (rather than basalt), material ejected from the summit, and ash layers. This type of volcano is commonly found in subduction zones; they tend to have explosive eruptions (e.g. Mt Saint Helens). The oldest rocks on Mt Rainier are about 500,000 years old. It is active and listed as a decadal volcano–one of the most dangerous volcanoes in the world. Its last major eruption, accompanied by caldera collapse, was 5000 years ago, but minor activity was noted during the nineteenth century.
Figure 2. From my home in Tacoma (star) it’s a two-hour drive to Mt Rainier National Park. It is part of the Cascades Range, which comprises many well-known volcanoes like Mt Baker, Mt St. Helens, and Mt Hood.
Figure 3. This photo was taken on the south flank at an elevation of about 5400 feet, near the visitor’s center. It was a beautiful day and there were a lot of people preparing for some cross-country skiing on a couple of feet of snow. From this elevation it takes 2-3 days to reach the summit, almost 9000 feet higher. It’s hard to imagine it being so high and taking so long to reach.
Figure 4. These southern volcanic mountains are part of the Tatoosh Range, with peaks of about 6600 feet. Most of the volcanic rocks comprising these mountains are andesite, intermediate in composition between basalt and rhyolite. It is also very viscous, behaving like peanut butter and thus not flowing well. Andesite is commonly found at convergent plate boundaries where it is thought to result from mixing of basalt (from the oceanic crust), continental crust, and sediments accumulated in the accretionary prism.
Figure 5. Map of the 28 glaciers on Mt. Rainier. The glaciers fill canyons and valleys that were partly cut by ice. Figure 3 shows a smooth mountain, but in reality most of the smooth areas are the surfaces of glaciers. We’ll look at one below. The ellipse indicates the area discussed in this post.
Figure 6. (A) Narada Falls interrupts the descent of Paradise River, fed by Paradise Glacier (see Fig. 5 for location), making it drop a couple hundred feet over a thick layer of andesite. Andesite tends to form blocky flows, as shown in the right side of the photo, where the water seems to be climbing down steps. (B) Possible contact between younger volcanic and older intrusive rocks. Igneous activity within the area has been continuous for at least 50 my, during which time erosion has exposed older intrusive rocks like this granodiorite, which is part of a pluton intruded between 23 and 5 Ma. It is important to keep in mind that the volcanic rocks originated in plutons (magma chambers) emplaced miles beneath the surface. As they are exposed, new volcanoes form as more magma is injected into the shallow crust in a continuous process. (C) Differential weathering has accentuated layering in this volcanic rock, which was probably created by a series of ash layers deposited in quick succession–geologically speaking.
Figure 7. (A) View looking north towards the source of Nisqually Glacier (see Fig. 5 for location), which originates near the peak of Mt Rainier. The area delineated by the blue rectangle is the face of the glacier. (B) Closeup of the face of Nisqually Glacier. The characteristic U-shaped valley carved by glaciers is highlighted in white. Note the dark material within the glacier, probably wind-blown fine sediment. It looks like the face is a couple hundred feet high. I’ve never seen a retreating glacier before, so this is pretty spectacular to me. The Nisqually River originates right here…
Figure 8. View looking upstream along Nisqually River a mile downstream from Fig. 7. This is one of the most stunning photos I’ve ever taken because it reveals geological continuity, from the origin of a glacier 10000 feet higher, to the outwash being transported by a river. Amazing! Note the perfect U-shape where the shadow ends upriver. This area would have been covered by the glacier as recently as 10000 years ago.
Figure 9. Another mile downstream from Fig. 8 the walls of the valley have lowered, and are now rimmed by volcanic flows half-buried by detritus. Evidence of a glacier filling the valley has been erased by collapse of the valley walls. Rounded boulders fill the riverbed. The Nisqually River is overwhelmed by the huge sediment load and opens up new channels to continue flowing.
Figure 10. View looking upstream at the confluence of Nisqually River and Van Trump Creek. There are a couple of interesting features visible in this braided stream bed, less than two miles from the glaciers feeding each branch. The valley is very wide and flat-bottomed because it was carved by glaciers more than 10000 years ago. The large boulders (as large as three feet) covering the entire valley floor were transported by a glacier and became relict after its retreat because the stream flow, even during floods, is too weak to transport and erode them. The Nisqually River is cutting a channel through these relict sediments; the scarp is about eight feet in height. The white line delineates large, surface boulders from subjacent sand and silt with few boulders. Note that the surface boulders stop upstream where the white line curves sharply upward.
Figure 11. Image from 200 feet downstream of Fig. 10, showing a break eroded in the boulder-bar that crosses the stream bed at an angle. During recent heavy rain Nisqually River broke out of its current channel and created a myriad of flow structures such as the longitudinal bars seen in the lower-right of the photo. I think this bedform is actually a terminal moraine marking the maximum advance of a previous glacier–not necessarily the maximum glacial extent during the last two-million years.
Figure 12. (A) Andesite boulder (2 feet across) wet by recent rain shows fine-scale structure. The irregularity of the laminae, and phenocryst distribution, suggest to me that this sample represents ash fall rather than a flow. Magma with the viscosity of peanut butter tends to form smooth lines because it is difficult to penetrate, which would be necessary to create the mixed-up appearance between the lighter and darker shades in the center of the image. (B) Large block (~10 feet long) of intrusive rock similar to that seen at Narada Falls (Fig. 6B), but this is two-miles downstream. This relic was pushed/dragged by a glacier to this location. The white circle indicates where a close-up photo was taken. (C) Close-up (5x) image of the heavy block. It contains quartz (Q), plagioclase/albite feldspar (no orthoclase) (F), and amphibole (Am). My estimate of the composition is: 50% feldspar; 30% quartz; and 20% amphibole. Based on my estimated mineral composition, this would be granodiorite; however, I didn’t differentiate plagioclase and albite feldspar. (The former is darker than the latter.)
Figure 13. Map of potential volcanic risks associated with Mt Rainier–besides an explosion (e.g. Mt St Helens) and the eruption of ash which would cover a large area, depending on wind direction. Lahars (mud flows fed by all those glaciers) pose the greatest risk because andesite is too viscous to flow more than a few miles from its source.
Summary. I have seen evidence of continental glaciers in the Great Plains, the German Plain, and Ireland, but I never had the opportunity to observe glaciers up close. Alpine glaciers were nothing more than an abstract idea to me, something viewed from a distance.
I’ve looked out over the clouds from the summit of Haleakala crater on Maui, gazed into the cauldron of Kilauea, witnessed the boiling water rising from beneath Yellowstone’s seething caldera. I’ve seen videos of volcanic eruptions in Iceland, but I never imagined putting the glaciers and volcanoes together–right next door!
Usually, geology is observed as a series of images frozen in time, but at Mt Rainier it can be glimpsed as a real-time process that reshapes the earth’s surface–from top to bottom.
What a wild geological ride!
Deception Pass: Ophiolite or Volcaniclastic Sediments?
Now that I have a general idea of the geologic history of Northwest Washington (NWA) it’s time to start filling in the blanks. I immediately found a discrepancy in the rocks found on the northern end of Whidbey Island and the adjacent peninsula (Fig. 1): some authors identified these rocks as ophiolite–pieces of ocean crust that contain evidence of extrusion at mid-ocean ridges. Let’s see what I found.
Figure 1. Whidbey Island is a large island that is almost completely covered by glacial sediments. Its elevation varies from less than 100 feet above msl (mean sea level) to almost 400 feet, probably reflecting the presence of terminal morraines deposited as glaciers retreated. The box encompasses the study area, and the star is my home in Tacoma.
Figure 2. Progressively more detailed maps of Whidbey Island, showing the geological formations discussed in this post. (A) Deception Pass is a narrow channel (~200 yards wide) between Whidbey Island and a tiny island that connects it to a peninsula. Glaciers covered this entire area, advancing and retreating for at least two million years, while scraping out Puget Sound from unconsolidated sediments and easily eroded rocks. I entered Whidbey Island via a ferry from the mainland just north of Seattle. (B) Geologic map of the norther tip of Whidbey Island and the adjacent peninsula. The tan areas are covered by glacial sediments whereas the blue and green areas are reported as volcaniclastic rocks by Rock-D and the US Geological Survey national map. However, I read a Washington State geological report from 1962 that reported layered gabbro and other indices of a classic ophiolite sequence. Were Washington’s geologists incompetent? Over eager? Non-peer-reviewed? Or maybe they stumbled onto an exposure, described it in a state report, and, when no one cared, dropped it until they retired. I don’t know. Nevertheless, everyone is in agreement that the age of these rocks, which include basalt and marine sediments, is poorly constrained: they could be as old as 251 Ma, the beginning of the Mesozoic era; and as young as 66 Ma–the end of the Mesozoic. Wow! The thin, black lines indicate faults inferred from stratigraphic relations. The USGS has adopted the generally accepted paradigm of gathering legacy geological formations into larger groups that reflect the plate tectonic setting, rather than geographic location. The “official” description is so encompassing (including the kitchen sink) that it could easily include what the Washington geologic report called “ophiolite”. (C) Detailed map showing my approximate location along the path that followed the shoreline (blue circle) and the location where I saw these rocks in an excellent exposure (yellow diamond). I’m not sure why the rocks south of Deception Pass (blue) are differentiated from those on the north side (green) by Rock-D; the USGS map shows they are the same, as does my field examination (discussed below).
Figure 3. The ferry ride from Mulkiteo to Whidbey Island (see Fig. 2A) shows the same high elevation of Whidbey Island (left), Hat Island (center), and a promontory north of Tulalip (behind the ferry; see Fig. 1). This elevation of glacial sediments is approximately the same as the basement rock discussed below. This high relief shoreline is found throughout Puget Sound.
Figure 4. View looking north across Deception Pass, showing the nearly vertical bedding of rock layers, which could be original sedimentary fabric, metamorphic surfaces, or joints. Let’s have a closer look.
Figure 5. Images of the exposed rocks near the top of the hill overlooking Deception Pass (see Fig. 2C for location). (A) These medium bedded (~6 inches) layers contain clasts of different rocks. The height of the image is about six feet. (B) This twelve-foot exposure shows thin-bedded sand/silt layers with intercalated mud, but the layers are overturned (more than 90 degrees from horizontal) and reveal rapid changes in bedding, in addition to large boulders of material. (C) A bedding surface shows the characteristic sheen of schist, which adds metamorphic foliation to original bedding. These rocks are not heavily altered, so the layers seen in (B) probably reflect original beds. The clasts in (A) are matrix supported, which suggests mixing of different sized particles. This unusual texture occurs in environments where periodic mass failures (e.g. landslides or submarine slides) occur.
Figure 6. These images from about 100 feet elevation show more details of the rocks exposed at Deception Pass: (A) These layered sediments vary from medium to thick bedded and they also reveal gentle folding at this scale (the photo is ten feet high), suggesting that the overturned beds may be part of a large fold, possibly related to the faults seen in Figs. 2 B and C; note that the faults have a NW-SE orientation approximately aligned with the fold axis (I didn’t make careful measurements). It is also possible that the faults reflect brittle failure as the rocks were uplifted within the accretionary prism. (B) The left half of the exposure reveals a thick (> four feet) layer containing mixed clasts in an otherwise fine-grained matrix. The right side contains medium beds of a lighter material (We don’t want to get carried away here because of the vagaries of chemical weathering.) However, the contact between the two apparent lithologies is irregular; If I’m right about the left side being the bottom (questionable), this could have been a volcaniclastic slide (basalt, ash, pieces of rock, etc) that was then filled in by less catastrophic sedimentation. I admit I’m speculating, but we have to imagine life on the continental margin during active volcanism, during subduction.
Figure 7. This photo was taken looking west from Deception Pass (see Fig. 1), towards the Pacific Ocean. Those islands are emergent blocks of jumbled Mesozoic/Tertiary sedimentary and volcanic rocks. The last ten-thousand years of sea level rise has covered most of the evidence contained within the accretionary prism, leaving us with only fragments.
Conclusion. I didn’t see any ophiolite at Deception Pass, but there is plenty of evidence of accretionary tectonics; deeply buried sediments and volcanics were scraped off the subducting oceanic crust and deformed continuously. This process has to obey the laws of conservation of mass, which means that the accretionary prism accumulates further west with each passing year. What we see exposed at the northern end of Whidbey Island is occurring today beneath the continental shelf, all while the Juan de Fuca plate is swallowed by the earth’s mantle. There is a two-mile-deep trench about 100 miles off NWA, but it is filled with sediment eroded from N. America, unlike more-familiar deep-sea trenches (e.g. the Mariana Trench, about 7 miles deep).
All that sediment in the subduction trench is like sand in in your transmission: it gums up the works and slows things down, but the Earth cannot be stopped, its relentless, insatiable appetite for oceanic crust never satisfied. It will keep chewing up the Juan de Fuca plate until the upper mantle decides that enough is enough and stops pushing N America westward.
I can’t wait to see how this ends…
Timothy R. Keen 
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