Seeing Volcanoes Inside and Out: Exploring California's Volcanoes

Our just completed exploration of Northern California's Volcanoes was a fascinating journey through the interior and exterior of several volcanoes. How do you explore the innards of a volcano? On the one hand, you can do a Brendan Fraser and fall thousands of feet or miles into a volcano ("Journey to the Center of the Earth", a movie I appreciated mostly for the living trilobite in the opening scene). Or...you can wait for the volcano to go extinct, be uplifted and eroded for millions of years, and then be established as Castle Crags State Park, and go stand at the viewpoint at the end of the park road. We chose the latter.

The Castle Crags are an especially scenic part of the Klamath Mountains province, a region tucked between the Coast Ranges and the Cascades at the north end of the Great Valley (I've written about them previously, click here to see). Most of the Klamaths are composed of dark colored metamorphic rocks, many of them derived from the mantle, but at Castle Crags the rocks are different. The light colored cliffs are composed of granitic rock (mainly granodiorite, a plutonic rock containing lots of plagioclase feldspar), dating back to around 160 million years ago. The granodiorite was once molten, feeding volcanoes that would have existed several miles above where we were standing. Some of the magma remained in crust, cooling slowly and allowing for the growth of visible crystals. Standing among the granitic towers of Castle Crags is to be standing in the interior of a volcano.

The dramatic spires are the result of exposure at the Earth's surface, and the resulting release of pressure (remember that these rocks formed at a depth of three or four miles in the crust). As the pressure is released, the rock expands and fractures, sometimes in vertical cracks called joints. The joints are exploited by water and ice, leading to the erosion of the steep sharp cliffs.

Sometimes the expansion of the granitic rock is outwards, parallel to the surface of the cliff. This causes fractures that act to remove corners and edges, resulting in dome-like cliffs, much like those found in Yosemite and elsewhere in the Sierra Nevada. This process is called exfoliation.

Even as we stood at the viewpoint appreciating the underside of a volcano, we could turn to our right and see a rather astounding view of the outside of a volcano. A very big volcano. Mt. Shasta is the second tallest peak in the Cascades Range, exceeded only by Mt. Rainier, but it is the most voluminous stratovolcano in the Cascades, and perhaps even the world.

At 14,179 feet, it dominates the scenery from all directions in Northern California. A stratovolcano is composed of alternating layers of ash and lava, but the details of Shasta's structure contradict that description. It is actually the remnant of at least five different volcanoes which developed on more or less the same site. The term "composite cone" is perhaps a more accurate moniker.

Shasta was our next stop of the day. At over 14,000 feet, no roads approach the summit, but in years past a ski area had been constructed at the 8,000 foot level on the south side of the peak. The ski resort was removed long ago because of avalanche danger (a wide swath of fallen trees highlights the hazard), but the paved road remains.

We took the highway out of Mt. Shasta City and headed up the mountain...

The Other California: Taking Stock of the Castle Crags

Driving on Interstate 5 north of Redding is a sometimes terrifying affair. The highway follows the Sacramento River in a winding canyon with plenty of twists and turns. The terror isn't necessarily the road itself as much as it is the giant trucks and recreational vehicles which are being driven as if they were still on a straight freeway in the Central Valley. They don't exactly stick to their lanes. The other hazard comes from following geologists on their way north to see Mt. Shasta: at a particular loop on the highway near Dunsmuir, they are very likely to slam on the brakes as the Castle Crags come into view...

This is part of my continuing series on the "Other California", an exploration of those wonderful parts of our state that don't always show up on the postcards. Today we are wrapping up a journey through the Klamath Mountains. It has not been an exhaustive survey as it is one of the corners of the state that I have yet to fully explore. I want to reiterate my invitation: be a geotripper geoblogger! Have you been to Shasta Caverns? Backpacking in the Trinity Alps? Explored any gold mines near Weaverville or Shasta City? Write a short narrative, or if you don't trust your writing skills, just send some nice pictures, and I will find something to say.

The Castle Crags are certainly a shock when first seen from Interstate 5. The light-colored cliffs rise 3,000-4,000 feet above the river canyon, and stand in stark contrast to the lower heavily forested ridges that make up most of the surrounding area. The peaks and domes remind some people of the Sierra Nevada, and the comparison is apt; the Crags are composed of granitic rock, and as noted previously, the Klamaths are a northern extension of the Sierra Nevada. Their geologic history is similar, with one big difference: the Sierra range is composed mainly of granite intrusions (plutons), but in the Klamath Mountains, the intrusions are smaller and isolated from each other.

A batholith is a single intrusion exposed over an area of 100 square kilometers (40 square miles), although the term can also refer to a vast agglomeration of many dozens of adjacent plutons, as is the case in the Sierra Nevada. There are several of these composite batholiths in the western United States, including the Sierra Nevada, the Idaho, and the Southern California batholiths. The Castle Crags and other small isolated plutons are referred to as stocks. The limited areal extent of the Castle Crags pluton is apparent in the photo below. The surrounding rocks are the more easily eroded metamorphic rocks of the Eastern Klamath Terrane (the Trinity Complex).

The rocks of the Castle Crags formed about 163 million years ago when the Pacific Plate sank beneath the edge of the North American continent in an extensive subduction zone (the same kind of subduction that produces the Cascades volcanoes in the present day). Water released from the descending plate acted like a catalyst leading to the melting of rock deep in earth's interior, and the resulting magma bodies rose until they lay just a few miles beneath the surface. The rock cooled slowly, over tens of thousands of years, forming granodiorite (a coarse-grained granitic rock with significant amounts of plagioclase feldspar). At times, magma reached the surface producing volcanic eruptions, but the volcanoes at Castle Crags have long been worn away. In other words, standing on the granitic rock of the peaks here, one is actually perched under a long-gone volcano.

The sharp spires and rounded domes of the Crags are the result of having a great weight removed. Having formed at depths of three miles or more, the rocks expanded as erosion removed the heavy overlying rocks. But rocks can't expand like marshmallows; they fracture, much like the crust of baking loaves of bread. Vertical cracks are joints. Closely spaced joints promote the formation of the spires and towers of granitic rock. Fractures parallel to the surface are called exfoliation sheets. Exfoliation tends to remove to remove corners and edges, resulting in the formation of domes (Half Dome in Yosemite is a half-good example).

The Castle Crags were also glaciated, but with top elevations of less than 7,000 feet, the glaciers were small, and had less to do with the overall shape of the mountains than jointing and exfoliation. A few small lakes and moraines are found on the north side of the peaks.

Castle Crags State Park honors the Castle Crags, but does not actually encompass them. The park boundaries include the heavily forested southern and eastern flanks of the crags, and part of the Sacramento River, but the granitic cliffs and domes are protected as the Castle Crags Wilderness Area, administered by Shasta-Trinity National Forest. The state park offers a nice campground, with several trailheads that provide access to parts of the wilderness, as well as 8 miles of the Pacific Crest Trail. A park road leads to a spectacular viewpoint that takes in the Crags and nearby Mt. Shasta.

Vennum, Walter, 1980, Petrology of the Castle Crags pluton, Klamath Mountains, California: Summary, GSA Bulletin; v. 91; no. 5; p. 255-258.

Vennum, Walter, 1994, Castle Crags, California Geology, March/April, pages 31-38.

The Other California: A Journey to the Center of the Earth (kind of...)

How many of you tried to dig a tunnel to China in the backyard when you were a kid? Given the soil conditions in the yard I grew up in, I'm probably lucky to be alive. I dug tunnels looking for buried treasures, gemstones, fossils and sometimes I was just curious what was down there. Geologists, I've found, are the kids who tried to find all those things, and never really grew up.

So how far do these overgrown kids get? It turns out that the deepest tunnels that humans have ever been able to dig reach depths of about 12,800 feet, a little over 2-1/2 miles. That might seem like a lot from our point of view, but the depth to the center of the Earth is around 4,000 miles. We've barely scratched the surface, yet the temperatures of the rock at these depths is well over 100 degrees, and the rocks are under so much pressure that explosions of rocks from the walls are a constant danger to the miners. Kids, there's got to be a better way to see what lies deep below. And there is, in the Other California, one of those places not found on the postcards. The adventure lies in the Klamath Mountains, and the most dangerous thing you have to face is slipping on a slick river rock, because geological processes have brought the rocks many miles up from the depths. You need only explore the rivers flowing off the mountains to see what the deep interior of the earth looks like.

The Klamath Mountains are a collection of bits and pieces of the earth's crust that have been carried great distances from their point of origin and slammed (at geologic speeds of inches per year) into the western edge of the North American continent. A huge variety of igneous and metamorphic rocks are found around the province, and some of the most interesting are those that once resided deep in the Earth's mantle, a layer that extends from just below the crust, from maybe 15 or 20 miles beneath our feet, to a depth of about 1,800 miles. Here are a couple of bits of the Earth's deep hidden places that I found on a short trip to the Eastern Klamath Terrane in the vicinity of Gazelle.

The oceanic crust is usually described as being made of basalt, but a few miles down in the crust the basaltic magma cools slowly to form a coarse-grained basaltic rock called gabbro. Sometimes, as can be seen above, the crystals that form are huge, with black hornblende and white feldspar crystals several inches long. Igneous rocks with such large crystals are called pegmatites.

Going even "deeper" into the interior, we pass the Mohorovicic Discontinuity, the dividing line between the crust and mantle. The upper part of the mantle is composed of olivine-rich rocks like dunite or peridotite. Olivine is best known to most people as the green gemstone peridot. That's right, much of the Earth's interior is made up of gems! The rock in the picture above is dunite, in part slightly altered to serpentine.

In many parts of the Klamath Mountains, the mantle rocks are completely altered to serpentine, the state rock of California. These ultramafic rocks are fairly rich in a number of unusual metal ores, including platinum, nickel, magnesium and mercury. One of the most important ores is chromite, which is the only significant source we have for chromium, the metal that puts the "stainless" in stainless steel. We import most of the chromium that we need from foreign sources, but in wartime (especially the two World Wars), the ores were mined domestically, and a number of operations were present in the Klamaths. The black semi-metallic crystals in the picture above are chromite, with green serpentine across the top.

In our next post we are going to "climb" into the underside of a volcano...

The Other California: I've Seen These Mountains Somewhere Before: The Big Ripoff!

This is an ongoing exploration of the "Other California"; the wonderful geological places in our state that are rarely found on a postcard. After some geological distractions (like giant earthquakes in Chile and tsunamis in Hawaii), we are back on the road looking at some peaks that look strangely familiar. They're made of granitic rock, they've been subjected to exfoliation and jointing, forming the sheer cliffs and rounded peaks. The mountains here have been glaciated. Where would you think we were, if you are a dyed-in-the-wool Californian?

If you guessed the Sierra Nevada, you would be wrong. And right, too, in a sense.

We started a tour of the Klamath Mountains talking about their origin as bits and pieces of oceanic crust and continental fragments that were assembled into a complicated exotic terrane that was attached to the North American continent in Mesozoic time. We followed up by discussing the alleged presence of Sasquatch in the region (though the discussion didn't last long; the Chilean earthquake proved far more interesting as a scientific issue that week).

Today we note the striking similarities between the Klamath Mountains and the northern part of the Sierra Nevada (see the map above). Both mountain systems have rocks that are primarily metamorphic sequences that have been intruded by Mesozoic granitic rocks. The metamorphic rocks are of similar age and structure. They have been faulted in much the same way. They are, in few words, the same mountain range, at least in the origin of the rocks. Direct correlations of the complicated metamorphic sequences have been established in recent publications by the US Geological Survey.

The oddest part of the story seems to be the overall shape of the two provinces. They look as if they were bent and torn apart from each other and separated by a distance of around 60 miles. And they were, around 140-150 million years ago, in late Jurassic or early Cretaceous time. A shallow sea opened between the two landmasses, and several thousand feet of sediments were laid down on the rocks (the Hornbrook Formation). It was a huge rip-off!

By Pliocene time (4 or 5 million years ago), the region was a flat low plain, but it rose rapidly, as much as 6,000 feet, in the last few million years. Rivers coursing across the flat surface quickly incised the deep canyons that characterize the region today (small gravel remnants of the rivers can be found on some of the higher parts of the topography).

The implications of the similarity of the two provinces was not lost on the Forty-niners. Gold was mined from the metamorphic rocks of the Sierra Nevada Mother Lode, and the rocks in the Klamaths were clearly of the same origin. Gold was discovered in the Klamaths in 1848, and numerous towns sprang up soon after. The region was the second most important gold mining region in the state of California after the Mother Lode, with several million ounces of gold produced.

For some recent research on the uplift history of the Klamath Mountains, check out: Cretaceous Sedimentary Blanketing and Tectonic Rejuvenation in the Western Klamath Mountains: Insights from Thermochronology

The "Other" California: Havin' Fun With Sasquatch

An exploration of the Klamath Mountains of California is not complete without a discussion of...well, let me mention a field trip story. The punchline isn't very exciting, but here goes.

We take a field studies trip to the Cascades every other September. To split up some of the long drives, we leave on a Thursday afternoon and drive to a state park on the Sacramento River near Red Bluff. We usually arrive about 9:30 at night, at which point we roll out our sleeping bags and get a good night's sleep before really starting our class the next morning. Sometimes we have complications. One time we arrived to find the entire campground occupied by a convention of ultra-libertarian, almost-militia type folks having a barter fair. We had to barter with a very drunk organizer who was suspicious that we were members of the federal guvmit to negotiate out a little corner of the campground for ourselves. We had kind of a nervous evening.

Another year we had a different problem: we arrived and the entire campground was closed for renovations! I wasn't quite prepared for this, and we headed north on the highway looking for another place to stay. It took us a couple of wrong turns looking for a non-existent camp along the Sacramento River ("it's on the map, dangit!"), but finally around midnight we found a KOA that was willing to take in 30 weary travelers on short notice (and for a price). It was nice of them to put up with us, but it was an unremarkable place except for the men's bathroom. It had a giant diagram on the wall of all the Sasquatch sightings in northern California! We were in Bigfoot Country!

A discussion of Bigfoot is going to carry us into fringe territory along with UFO's, Lemurians, Atlantis, ghosts and who knows what, but at least Bigfoot is regarded as "fun". No one seems to think that they are plotting to take over the human race, or that they are attacking and eating people (apparently president Theodore Roosevelt provided the only exception).

So why won't biologists and other scientists accept the existence of Sasquatch? After all, there have been hundreds, maybe thousands of reported sightings, along with dozens of photos and footprints, especially since 1958 when tracks were found around the equipment at a logging camp (tracks made by the company owner to scare away vandals). We live in a visual society...why aren't photos enough?

I've been having fun reading some discussions lately about whether Yosemite's Half Dome can be seen from the floor of the Central Valley in California. The main evidence lies in a dozen or so photographs that have been posted on the internet by different individuals (including me). The interesting aspect of the discussion has been the many skeptics who insist that Half Dome absolutely cannot be seen from the valley, and who charge that the photos are an elaborate photographic hoax. So...a few people say it CAN be seen and offer a few grainy photographs, versus expert photographers and hikers who clearly know that it CAN'T. Isn't this the same situation that we have with Sasquatch?

Not really equivalent at all. Despite any arguments and calculations that can be offered by detractors, all one has to do is go to the right spot on an unusually clear day in the Central Valley, and there it is. Half Dome isn't going anywhere, and confirmation is easily achieved.

On the other hand, if Bigfoot-Sasquatch were an actual living species, the implications would be staggering. A second hominid species, a large one, living in North America alongside humans would be an astounding discovery. How did it evolve? How closely related is it to Homo sapiens? How can it have escaped discovery despite the intense development of the western states and the intense logging activity in the places where the species lives? And if the existence of the creature were to be in some way confirmed, what are the legal ramifications? Endangered Species Act? Would they be placed on reservations? (yes, that question is an indictment about government attitudes about First Nation/Native American people). In a word, it would be extraordinary.

So here is the problem: there isn't a shred of physical evidence that Bigfoot exists that can be subjected to any kind of scientific scrutiny: there are no bones, either recent or ancient, no droppings, no nesting/bedding sites, no artifacts, no bodies, no fur. Wildlife biologists will happily admit they were wrong when the physical evidence appears, but in a century of searching, nothing has emerged.

And consider something else: motivation. When we were accused (in a good-natured way, I hope) of being hoaxers in the Half Dome affair, I would have to respond: what do we have to gain? No one is going to pay us thousands of dollars for a grainy, slightly out-of-focus picture of Half Dome (not that I would turn down an offer!). But if I said I had a genuine picture of a Sasquatch (and I were a talented photo-manipulator; see the photo above!), I could potentially earn a fair amount of publicity and cash, even if the photo is later revealed to be retouched (the picture above is real, dangit, I swear it with my fingers crossed!).

Could Sasquatch really exist? Of course. But it is extremely unlikely. The evidence to confirm the existence of Bigfoot would have to be overwhelming. A century ago, a German meteorologist named Alfred Wegener said that continents had been drifting about the planet. Scientists were unconvinced by his evidence, which involved rock similarities, fossil similarites, and paleoclimate similarities. It was good scientific data, but geologists were able to offer alternative explanations that did not require movement of continents. It wasn't until new discoveries in the 1950's and 1960's in unexpected disciplines like paleomagnetism, and new technology became available that revealed details of the ocean floors that Wegener's hypothesis was accepted. In the process, the idea grew into a much more encompassing theory called plate tectonics (make no mistake: a theory is accepted scientific fact; it is hypotheses that are unconfirmed potential explanations). The fact that his hypothesis came to be accepted doesn't mean that any fringe science is automatically true. Scientists in all disciplines pretty much have to be skeptics by nature, and fringe ideas must meet the same exacting standards of evidence that any other hypotheses must meet.

The Other California: The Flotsam and Jetsam of an Ancient Ocean Basin

Map derived from Correlation of the Klamath Mountains and Sierra Nevada by W.P. Irwin

After a busy couple of weeks in other places, I'm getting back to the Other California, the exploration of the places in my fair state that don't always show up on the postcards...

In most parts of the world, the geological story can be teased out by following some basic rules of stratigraphy: in a sequence of layers, the oldest is usually found at the base; if a layer appears in the side of a cliff, we can reasonably expect that it will found to continue at another location nearby. Sediments usually form in horizontal layers. These principles were realized three hundred years ago by Nicolas Steno, and ultimately led to the establishment of geology as a science. Geologists were able to use these principles and a growing knowledge of sedimentary structures and facies to work out a reasonably accurate story of the history of the crust in many parts of the world. In regions like the Alps of Europe and the Appalachian Mountains in the eastern United States, the early geologists were able to unscramble incredibly complex rock sequences because they were able to correlate formations from one mountain ridge to another. Fault lines were not necessarily a problem; walk far enough and you could find a continuation of your missing layers somewhere along the other side of the fault.

The rules seemed to apply, until the geologists arrived in California. There are places in the state where the rocks are so chaotic and discontinuous that geologists with the classic training in stratigraphy had to throw up their hands in frustration. Following an outcrop? Great, there's a fault. We'll look for a continuation of the layer. And look. And look some more. And never find it. What are these older rocks doing on top of these younger rocks? That doesn't make sense. And why can't we find any fossils in many of these rocks? They're sedimentary, they should have fossils. California was an enigma and a chaotic mess to the first geologists who tried to pry loose her secrets in places like the Coast Ranges, the Transverse Ranges, and the Sierra Nevada.

There is a region that is pretty much the epitome of the chaos that is California geology. Tucked between the Cascades and the Coast Ranges of Northern California, the Klamath Mountains rise to elevations of just over 9,000 feet, and essentially resemble a large plateau that has been deeply dissected by stream erosion, especially along the Trinity and Klamath Rivers. The Klamaths are divided by geographers into a number of subordinate ranges, the Siskiyous, the Trinity Alps, the Marble Mountains, and others, and most of the country is untrammeled wilderness.

The Klamaths are a lesson in geology contradictions. Almost every kind of marine environment shows up somewhere, shallow nearshore deposits, coral reefs, carbonate shelves, deep ocean muds and trench deposits, but in close proximity are found unusual igneous rocks derived from the deep mantle and the base of the ocean crust. Here and there the rocks are intruded by granitic plutons much like those of the nearby Sierra Nevada, but also there are granites that are much older. Everywhere there are faults. Mostly they are thrust faults but occasionally normal faults are found, indicating that both compressional and extensional forces have affected the rocks.

The key to unraveling the mysteries of the Klamath Mountains was to stop trying to make logical sense of the rocks! There was not a single sequential story to be deciphered for this part of the world at all, there were a multitude of stories, stories that unfolded in many different places around the planet. One of the first researchers to make this connection, W.P. Irwin (in the early 1960's), divided the rock sequences into a series of "belts" that seemed to have originated in places other than the Klamaths. This model evolved into the concept of accreted terranes, a pioneering idea that played a central part in the acceptance of "continental drift" and plate tectonic theory in the late 1960's.

A terrane is a term used to denote:

...a fault-bounded geologic region that differs from adjoining geologic regions by its distinctive stratigraphy, structure, tectonic history, and in some cases biota ...Terranes may be either allochthonous or autochthonous, far-traveled or near their point of origin. Terranes may amalgamate together to form a superterrane, and terranes become accreted terranes after they collide with continental crust along an active plate margin.*

Translated, a terrane is the crustal equivalent of the debris that collects in a river eddy: the floating branches, leaves, bits of styrofoam coolers, and plastic bottles. In this case, the Klamath Mountains were a collecting point of various bits of ocean crust and continental fragments in the eastern Pacific region during Paleozoic and Mesozoic time.

Four major terranes were originally identified in the Klamaths by Irwin: the Eastern Klamath, the Central Metamorphic, the Western Paleozoic and Triassic, and the Western Jurassic. With continued research, these have been subdivided into many subterranes. A hint of the complexity can be discerned in the geologic map shown above, which is part of an effort to correlate the terranes of the Klamath Mountains to those in the northern Sierra Nevada.

A bit of a plea: Geotripper needs your help! I've explored a lot of California, but not so much in the Klamaths. Do you have a favorite spot you would like to share? Be a Geotripper Geoblogger for a day, and tell us about it!

*The Terrane Puzzle: New Perspectives on Paleontology and Stratigraphy from the North American Cordillera, edited by Robert B. Blodgett, and George D. Stanley, Jr.; Geological Society of America Special Paper 442, page 2.