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Washington’s waterfalls–behind each one is a rock!

Of all the many reasons why waterfalls are great, here’s another: they expose bedrock! And that bedrock tells a story extending back in time long long before the waterfall. This posting describes 9 waterfalls that together paint a partial picture of Washington’s geologic history. The photos and diagrams will all appear in my forthcoming book Roadside Geology of Washington (Mountain Press) that I wrote with Darrel Cowan of the University of Washington.

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Rainbow falls along WA 6 in the Coast Range

And waterfalls in heavily forested areas are especially great because they may give the only view of bedrock for miles around! Take Rainbow Falls, for example–the small waterfall on the left. It’s in Washington’s Coast Range along State Highway 6–a place where a roadside geologist could otherwise fall into total despair for lack of good rock exposure. But this beautiful waterfall exposes a lava flow of the Grande Ronde Basalt, which belongs to the Columbia River Basalt Group. Significant? Yes!

This lava erupted in southeastern Washington and northeastern Oregon between about 16 and 15.6 million years ago and completely flooded the landscape of northern Oregon and southern Washington. We know how extensive these flows are because we can see them–and they cover the whole region. The photo below shows them at Palouse Falls in the eastern part of Washington. Take a look at my earlier blog post about the Columbia River Basalt Group? (includes 15 photos and a map)

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Palouse Falls in eastern Washington drops more than 180 feet over lava flows of the Grande Ronde and Wanapum members of the Columbia River Basalt Group.

You might also notice in the photo above that the waterfall is actually pretty small compared to its amphitheatre. That’s because Palouse Falls is part of another flood story –of the Ice Age Floods, described in rich detail on the Ice Age Floods Institute website. Basically, some 40 or 50 gigantic floods coursed through the area towards the end of the Ice Age, between about 15-18,000 years ago. and among other things, carved this canyon. Lobes of the continental ice sheet repeatedly dammed the Clark Fork River in northern Montana and then failed, repeatedly, after forming Glacial Lake Missoula. Imagine the flow volume in the above photo multiplied more than 100,000 times!

Mount Rainier and the Cascade Volcanoes
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At 14,410 feet above sea level, Mount Rainier is the highest volcano in the Cascade Range –and one of the highest spots in the conterminous United States. The volcano itself consists mostly of andesite flows that date back nearly a half million years.

Beneath those lava flows are older rocks that speak to a history of volcanic activity reaching back 70 times that of Rainier’s oldest lavas –to about 35 million years ago. At Christine Falls, you can inspect granitic rock of the Tatoosh Pluton, which is a crystallized magma chamber that formed beneath some early Cascade volcanoes. It was probably active at different times between 26-14 million years ago. At Narada Falls, you can see where Rainier andesite actually flowed over the top of the granite–which tells us that the granite was exposed at the surface 40,000 years ago when that flow erupted. Both these waterfalls are right along the road that winds its way from Longmire up towards Paradise Meadows.

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Christine Falls (left) cuts through granitic rock of Tatoosh Pluton; Narada Falls (right) flows over Rainier Andesite that itself flowed over Tatoosh granodiorite, exposed on the rocky hillside.

If you go to the south entrance of the national park, you can walk a quarter mile from the highway to Silver Falls and exposures of Rainier’s oldest rocks. The Ohanapecosh Formation, made mostly of tuffs and re-deposited volcanic particles, formed by explosive volcanic activity that stretches back 35 million years. The Ohanapecosh Formation forms cliffs throughout much of the national park –and shows up northward as far as Interstate 90.

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Silver Falls in Mount Rainier National Park, spills over outcrops of Ohanapecosh Formation, the park’s oldest rock.

Finding the oldest volcanic rock in the Cascade Volcanoes is important because this incredibly active volcanic chain is fueled by magma generated through the sinking of oceanic lithosphere at the Cascadia subduction zone –and the oldest rocks allow us to estimate when this process started. They get even older at Snoqualmie Falls, just north of I-90. There, rocks of the Mount Persis Volcanics reach ages of 38 million years. Most geologists agree that for Washington, these rocks mark the first volcanic activity after the formation of the Cascadia subduction zone.

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Snoqualmie Falls drops more than 250′ into a gorge of Mt. Persis Volcanics –rocks that mark the onset of volcanic acitity related to today’s Cascadia subduction zone.


Early Volcanic Roots and Continental Accretion

Here it gets a little complicated, because subduction also drove much of Washington’s geologic history before the Cascade volcanoes started to form. This older subduction also formed volcanic chains and through the process of continental accretion, caused Washington to grow westward.

Intro-8. Accretion series-CS4This diagram, modified from my book Roadside Geology of Oregon, illustrates the process of accretion. Basically, some element of the subducting seafloor is unable to fully sink beneath the continent, probably because it’s topographically high– such as with a series of seamounts. This material jams up the subduction zone and causes the sinking to stop temporarily. Eventually, a new subduction zone forms farther offshore and the thing that jammed up the zone in the first place gets added, or accreted, to the edge of the continent. In Washington and Oregon, the younger Cascadia subduction zone is the one that formed the Cascade Volcanoes and the stuff that jammed the zone was a huge fragment of oceanic lithosphere called “Siletzia”. Siletzia now makes up the bottom of Washington and Oregon’s Coast Range. The older subduction zone that got jammed up is the one that’s responsible for the rocks described below.

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Gorge Creek cuts a slot through orthogneiss (inset) of the Skagit Gneiss Complex along State Highway 20 in Washington’s North Cascades.

Gorge Falls along State Highway 20 in the North Cascades cuts this narrow slot through rocks formed because of that older subduction zone. These rocks started as the granitic roots to volcanoes, much in the same way as the Tatoosh Pluton formed the roots to some Cascade volcanoes. Those roots then got squeezed and reheated to make a metamorphic rock called gneiss. In some places it even partially re-melted.

The inset gives a close-up view of the rock. It’s called “orthogneiss” because it started out as an igneous rock. It forms a big part of the Skagit Gneiss Complex, which makes up the core of the North Cascades.

It’s hard to say if the Skagit Gneiss Complex was actually added to the edge of North America from somewhere else, but a lot of other rocks in Washington were–and those episodes of accretion are what caused much of the metamorphism in the North Cascades.

 

For accreted rock, here’s probably my favorite waterfall: Nooksack Falls, along State Highway 542 between Bellingham and the Mt. Baker ski area. It’s made of conglomerate of the Nooksack Group, which accumulated in a submarine fan somewhere off the coast of North America during the Jurassic and Cretaceous Periods, maybe 140 million years ago.

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Nooksack Falls in the North Cascades. the horizontal lines across the falls mark traces of bedding in the rock that’s inclined directly upstream.

Ancient North America

If you go eastward towards Spokane, you eventually find yourself on the North America that existed before all this accretion. Of course, much of the area is now covered by the Columbia River Basalt, but in the northeast corner of the state, you encounter Paleozoic sedimentary rocks that formed along the continental margin of that older continent. Sweet Creek Falls is one place to see these rocks, right off State Highway 31. There, the beautiful stream spills over ledges of Ledbetter Slate, deposited as shale during the Ordovician Period. In the foreground are cobbles of Addy Quartzite, formed as beach-deposited sandstone in the Cambrian.

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Sweet Creek Falls spills over Ledbetter Slate. Cobbles of Addy Quartzite lie in the foreground.

 

Washington’s Geologic Timeline

The timeline below shows Washington’s main geologic events –and you can see where these 9 waterfalls fit. The red text and red-colored bars represent geologic events represented by individual waterfalls, shown in blue.  Kind of amazing… these 9 waterfalls show many of Washington’s most important elements: the Cascade Volcanoes, the Columbia River Basalt Group, continental accretion, and the old continental margin.

And they’re nice places to hang out!

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Timeline of Washington’s geology. Red text signifies events described in this post and represented by various waterfalls (in blue).

 


For more geology photos, please check out my website–it contains a searchable database of more than 2000 geology photos for free download.

Roadside Geology of Washington should be out and available in August, 2017.

Thanks for reading!

 

 

 

 

 

Death Valley National Park– Geology Overload!

Death Valley… I can’t wait! Tomorrow this time, I’ll be walking on the salt pan with my structural geology students, gawking at the incredible mountain front –and soon after that, we’ll be immersed in fault zones, fractures, and fabrics!

Death Valley salt pan at sunrise.

Death Valley salt pan at sunrise.

Death Valley presents incredible opportunities for all sorts of geology, especially geologic time; you can look just about anywhere to see and feel it.  Take the salt pan.  It really is salt –you can sprinkle it on your sandwich if you want.  It’s there because the valley floor periodically floods with rainwater.  As the rainwater evaporates, dissolved salt in the water precipitates.  And some 10,000 years ago, Death Valley was filled by a 600′ deep lake, which evaporated, leaving behind more salt. Before that, more shallow flooding and more lakes.

Aerial view of faulted front of the Black Mountains.

Aerial view of faulted front of the Black Mountains.

But the basin is more than 4 miles deep in some places! It’s not all salt, because there are a lot of gravel and sand deposits, but a lot of it is salt.  That depth speaks to geologically fast accumulation rates, because it all had to accumulate since Death Valley formed –probably in the last 2 or 3 million years.  But still, 2 or 3 million years is way past our realm of experience.

Hiker in the Funeral Mountains of Death Valley.

Hiker in the Funeral Mountains of Death Valley.

To really go back in geologic time though, you need to look at the mountains. Most of the mountains contain Upper Precambrian through Paleozoic sedimentary rock, most of which accumulated in shallow marine environments.  There’s a thickness of more than 30,000 feet of sedimentary rock exposed in Death Valley! Deposited layer after layer, you can only imagine how long that took.

We can measure the thickness of the rock because it’s no longer in its original horizontal position.  The ones in the photo above were tilted by faulting –which occurred during the period of crustal extension that formed Death Valley today.  The rocks in the photo below were folded –by a period of crustal shortening that took place long before the modern extension.  The folding occurred during the Mesozoic Era –more than 65 million years ago.

Aerial view of Titus Canyon Anticline.

Aerial view of Titus Canyon Anticline.

Above the Upper Precambrian to Paleozoic rock are thousands of feet of volcanic and sedimentary rock, tilted and faulted, but not folded. They reveal many of the details of the crustal extension that eventually formed today’s landscape.  For example, the photo below shows Ryan Mesa in upper Furnace Creek Wash.  In this place, the main period of extensional faulting predates the formation of modern Death Valley.  Look at the photo to see that faulting must have stopped before eruption of the dark-colored basalt flows.  Notice that there has to be a fault underneath the talus cones that separates the Artist Dr. Formation on the left from the Furnace Creek Formation on the right.  Because the fault does not cut the basalt though, it has to be older.  Those basalts are 4 million years old, older than modern Death Valley.  –And that’s the old mining camp of Ryan perched on the talus.

Angular unconformity at Ryan Mesa: 4 Ma basalt flows overlying faulted Artist Drive (left) and Furnace Creek (right) formations.

Angular unconformity at Ryan Mesa: 4 Ma basalt flows overlying faulted Artist Drive (left) and Furnace Creek (right) formations.

And beneath it all? Still older rock!  There’s some 5,000 feet of even older Precambrian sedimentary rock, called the “Pahrump Group” beneath the 30,000 feet of Upper Precambrian and Paleozoic rock–and below that, Precambrian metamorphic rock.  It’s called the “basement complex” because it’s the lowest stuff.  Here’s a photo.

pegmatite dike and sill intruding mylonitic gneiss

pegmatite dike and sill intruding gneiss

The pegmatite (the light-colored intrusive rock) is actually quite young–I think our U-Pb age was 55 Ma –but the gneiss is much older, with a U-Pb age of 1.7 billion years.  Billion!  Forget about the U-Pb age though.  These rocks form miles beneath Earth’s surface –and here they are, at the surface for us to see. Without knowing their age, you’re looking at deep geologic time because of the long period of uplift and erosion required to bring them to the surface.  And it happened before all those other events that described earlier.

THIS is why, when visiting Death Valley, you need to explore the canyons and mountains –not to mention the incredible views, silence, stillness…


Some links:
Geologic map of Death Valley for free download
Slideshow of Death Valley geology photos

–or better yet, type “Death Valley” into the geology photo search function on my website!

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.

Geologic history of the western United States in a cliff face in Death Valley National Park

Of the many geologic events that shaped the western United States since the beginning of the Paleozoic Era, five really stand out.  In approximate chronological order, these events include the accumulation of tens of thousands of feet of sedimentary rock on a passive margin, periods of compressional mountain building that folded and faulted those rocks during much of the Mesozoic–likely driven by the accretion of terranes, intrusion of subduction-related granitic rock (such as the Sierra Nevada) during the Jurassic and Cretaceous, volcanic activity during the late Cenozoic, and mountain-building by crustal extension during the late Cenozoic and continuing today.  This photo on the western edge of Panamint Valley in Death Valley National Park of California, captures all five.

View of canyon wall on west side of Panamint Valley in SE California --part of Death Valley National Park.  See photo below for interpretation.

View of canyon wall on west side of Panamint Valley in SE California –part of Death Valley National Park. See photo below for interpretation.

The photograph below shows an interpretation.  Paleozoic rock is folded because of the Late Paleozoic-early Mesozoic compressional mountain-building; it’s intruded by Jurassic age granitic rock, an early phase of Sierran magmatism that took place just to the west; the granitic rock is overlain by Late Cenozoic basalt flows, and everything is cut by a normal (extensional) fault.  And there is also a dike that cuts the Paleozoic rock –probably a feeder for the basalt flows.

Interpretation of top photo.

Interpretation of top photo.

So this is all nerdy geology cross-cutting relations talk –but here’s the point: in this one place, you can see evidence for 100s of millions of years of Earth History.  Earth is old old old!  THAT’S why I love geology!

And for those of you who crave geologic contacts?  This photo has all three: depositional, between the basalt and underlying rock; intrusive, between the Mesozoic granite and the folded Paleozoic rock; fault, the steeply dipping black line between the basalt and the Paleozoic rock.  Another reason why I love geology!


click here to see photos and explanations of geologic contacts.
or click here for a slideshow of Death Valley geology.

Geologic Time in a mountainside –the Wallowa Mountains from Joseph, Oregon

Joseph, Oregon is a wonderful place for geology.  The town sits right at the foot of the Wallowa Mountains in the northeastern corner of Oregon.  The mountains rise some 4-5000′ abruptly from the valley floor along a recently active normal fault.

The Wallowa Mountains rise along a fault zone just south of the town of Joseph.

The Wallowa Mountains rise along a fault zone just south of the town of Joseph.

In the mountains, you can see some bedrock relations that speak to great lengths of geologic time.  An erosional remnant of the Columbia River Basalt Group caps Sawtooth Peak in the photos below; it sits directly on granite of the Wallowa Batholith –and just a little bit south, on the next peak, the granite intrudes Martin Bridge Limestone!  So, from oldest to youngest, the rock units are the Martin Bridge Limestone, the Wallowa granite, the Columbia River Basalt.

Sawtooth Peak (right) capped by Columbia River Basalt.  Beneath it is granite of the Wallow Batholith --and off to the left, are the bedded rocks of the Martin Bridge Limestone.

Sawtooth Peak (right) capped by Columbia River Basalt. Beneath it is granite of the Wallowa Batholith –and off to the left, are the bedded rocks of the Martin Bridge Limestone.  See below for labels.

Rock units and contacts described in the text

Rock units and contacts described in the text

Never mind that we know the Martin Bridge Limestone is Triassic –so more than 200 million years old –and that the Wallowa Batholith formed at different times between 140 to about 120 million years ago –and that the basalt is about 16 million years old.  You can throw out radiometric dating, but even so, you’re looking at a great span of geologic time.  The limestone first had to be deposited, layer after layer –and then buried –and then intruded at a depth of 5-8 km by the granite –which THEN had to get uplifted to Earth’s surface so the basalt could flow over it.  After THAT, it all had to get uplifted to its present elevation along the normal fault just south of town and much of the basalt had to erode away.

Honestly, we have influential people in this country who spout off things like the Earth is only 6000 years old.  They also deny the overwhelming evidence for climate change.  I guess I should stop writing now before I get too worked up!


More photos of the Wallowas at Geologic Photography.

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