Seeing Volcanoes from the Inside Out: A Visit to Castle Crags State Park in California

We recently completed a rather awesome trip to study the volcanoes of California, most particularly those that are found in the northern part of the state. Nearly all of our sites were the result of recent volcanic activity like Mt. Shasta, Lassen Peak, and Medicine Lake Highland, but our first visit was unique: we were exploring a volcano from the inside out!

It's not easy to visit the underside of a volcano when you think about it. The magma chamber that feeds the volcano may be four or five miles underground, and the temperatures and pressures are far, far beyond the abilities of human technology to conceivably hope to visit any time soon (there is that Unobtainium that was used in Avatar and The Core, but folks might be surprised to find it doesn't exist). About the only thing we can do is be patient. Really, really patient. First, we need to let the hot magma cool down slowly, a process that may take tens of thousands of years. Then we need to wait for a mountain-building event to cause the crust to be uplifted several miles, and then wait for the forces of erosion to remove all of the overlying rock. That's a bit longer, at least several tens of millions of years. But once it's done, the magma chamber will be sitting there, exposed for all to see. Luckily for us, this exact sequence of events took place in the Klamath Mountains of Northern California, just a few miles away from Mt. Shasta. It's a state park called Castle Crags.

The first view of Castle Crags is dramatic. Driving north on Interstate 5, one is treated to miles of forested hills, but at Castella the hills give way to sheer cliffs and spires of granitic rock. The granitic rock exposed in the Crags is the visible evidence of a magma chamber that once fed volcanoes in the along the western margin of North America in the age of dinosaurs 165 million years ago.

The sharp spires and rounded domes of the Crags are the result of having a great weight removed. Having formed at depths of four 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.

We didn't have the time to hike among the trails that reach the base of the crags, but we stopped along Castle Creek to see what's been carried down the mountain by the glaciers and rivers that tear away at the granite. We could also see the more ancient metamorphic rocks that had been intruded by the granitic rock.

Seen from above (the picture below was taken on a lucky day flying home from Canada a few years back), the Castle Crags can be seen as isolated mass of granitic rock. In our geology textbooks, we find that a batholith is a single intrusion exposed over an area of 100 square kilometers (about 40 square miles). 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 surrounding rocks are the more easily eroded metamorphic rocks of the Eastern Klamath Terrane (the Trinity Complex).

We finished our subterranean exploration of the ancient volcano and headed back to the Earth's surface to find a more modern version of a volcano: Mt. Shasta. More on that incredible mountain in the next post.

Cartoons Come to Life: The Value of Field Studies at Red Rock Canyon

I spend a lot of time in classrooms drawing cartoons. Lots of them, diagrammatically representing folds, faults and stratigraphy, trying to communicate to my students how these structures tell the story of the Earth. The problem for many of my students is that these are just cartoons. Cartoons on Saturday mornings (do ANY of you remember when that was the only time one got to watch cartoons?) do represent life in a way, but only if you have a real life to compare them to. And that's the problem for many students these days. They have no real-life experiences in the outdoors with which to compare these drawings.

And thus, the value of a field studies course. There is nothing quite like having the privilege of standing beneath a cliff, enjoying and appreciating the scenery, yes, but also being able to understand the story it tells. Our trip to Death Valley a few weeks ago included a fossil hunt at the first stop, but our second was a site where basic principles of geology stand out in stark relief, without a need for a chalkboard cartoon (I forgot the chalkboard this trip anyway). We had arrived at Red Rock Canyon State Park in the Mojave Desert. Just stepping out of the vehicles presented us a cliff face that was a physical representation of the diagram at the top of the post, a series of brightly colored layers of sand, siltstone and volcanic tuff transected by a fault.

The order of the layering provides a fine example of "superposition", the principle that layered rocks are stacked oldest to youngest, unless they have been overturned. This is one of the earliest principles of geology, described originally by Nicolas Steno in the 1600s. Looking east along the cliff we could also see the physical manifestation of another Steno principle, that of original horizontality. Most sedimentary environments produce horizontal strata (think floodplains or lakes, or shallow seas). If layers are tilted, some kind of force has acted on them, and being here in southern California, faults might be at fault.

A discussion of these basic principles was followed by a short "mapping" project. We weren't quite to the proficiency of working with maps, but the students set out to propose how they would organize the layers into formations and members that could be used to tell a logical story as to how these rocks could have come to have the structure and appearance they have today.

Red Rock Canyon does have a fascinating story as it turns out. The red and brown layers, called the Dove Springs Formation, record deposition of silt and sand in river floodplains and ephemeral lakes between 12.5 to 7.5 million years ago. The semiarid savanna environment supported a diverse ecosystem that included extinct elephants (gomphotherium), ancestral rhinos, three-toed horses, giraffe-like camels, saber-toothed cats, and bone-crushing ancestors to the bears and dogs. There are also numerous smaller fossils like ancestral skunks, alligator lizards, and shrews, with a total plant and animal species count of more than one hundred. The ecosystem suffered the occasional catastrophe as it was buried by volcanic ash. Basaltic lava flowed across the region.

One of the student's discoveries was a somewhat less visible fault that shifted the layers. It was a great introduction into the mind of field geologists, seeing the world the way earth scientists do. It was an interesting spot, but there were many more to come on the road ahead.

Speaking of roads and cartoons come to life...here's the Roadrunner (pic is actually from Joshua Tree National Park)....

...and Wiley E. Coyote. Despite living in the most desolate driest place in North America, it looks like this one has actually caught a few roadrunners! Seriously, this coyote lives only a few miles from Badwater, the hottest and lowest part of Death Valley.

Why it's Nice to Teach in California: It's Field Season All Year!

I'm not sure when or why being in California became a "negative" thing. Sure, we have our urban areas and horrible traffic and air pollution, wildfires, and long droughts. But on the other hand, we have the most diverse set of geological landscapes to be found anywhere on the planet. One can quite seriously work on a tan at the beach, jump in a car and go skiing, and then slide down a sand dune in a desert all in a single day. And for us geologists who teach? We have the longest field season possible! When the last field trip of the fall semester ended, it was mid-November. We had a pleasant warmish day in Pinnacles National Park. Then there was the long, long winter grind. There was that month in December when we got all the rain. Then there was the driest January in our recorded history. And now, in mid-February, it's field season again!

This afternoon I will be taking a class on the road for the next five days, exploring the lands in and around Death Valley National Park. Temperatures are expected to be in the 70s or low 80s. I'm looking forward to being on the road again!

I'm not gloating about those of you who have been inundated in snow. It's not an easy time, and we have our problems of a different nature. The drought is very serious. But I still have to say that I don't understand people who think California isn't a nice place to live. To a geologist, it is paradise!

Web access will be pretty limited, so Geotripper will be back next week...

The Holidays Come Early at the Great Valley Museum: A Big Toothy Predator Arrives

So, I got a call the other day from Receiving..."You've got a giant crate that's been delivered. Where do you want it? And I think "Huh? I don't remember having anything on order". And then in the fog of my brain (it's finals week; I'm more addled than normal), a vague memory emerges: we ordered something a year ago! And it finally arrived!

The crate was indeed huge. We had to remove close to two dozen screws, and like the father in the movie "A Christmas Story" ("fra-gee-lay"), we found a great deal of stuffing. But slowly it emerged: Jaws. Very big jaws.

The children of the Great Valley are impoverished and are poorly served by a state that sometimes has other priorities than education (can you spell "prisons" or "tax breaks for the rich"?). Few of the students have spent much time beyond the boundaries of their own towns, and have little knowledge of the natural world that lies beyond the housing developments and farms. The Great Valley Museum at Modesto Junior College has labored for years to teach our children about the rich ecosystem that once existed here (and still exists in small pockets here and there), but the exhibits languished in a modified 80 year old converted house. At long last this is changing, and we are on the verge of opening up the new museum on the bottom floor of our Science Community Center in just a month or two.

The museum will be an essential destination for learning about the natural history of the Great Valley and surrounding regions. Now, I'm all for this kind of thing (just take a short look at my other blog, for instance), but the unfortunately sad other fact is that practically no one in our county is familiar with the incredible paleontology of our region. Mention "digging for fossils" and most people think dinosaurs, and invariably dinosaurs in some other place. But the history of our planet is much more than just dinosaurs, and our region is richly blessed with an incredible fossil record of strange and wonderful creatures that have lived here through the ages. I've discussed them in the past, and will do so again, but today's arrival was a special part of our fossil heritage.

In the waning part of the dinosaur era (the Mesozoic), a creature related to the Komodo Dragon adapted to living in a marine environment, becoming one of the top predators of their time. Upwards of 30-40 feet long, the Mosasaurs were terrifying, with massive teeth, huge jaws, and presumably a huge appetite for anything that swam the seas. They have been found worldwide, and several have been found in the sediments of the Great Valley Group. An excellent specimen of a creature called Plotosaurus bennisoni was discovered in our county by a young man from Gustine in the 1930s. They were here! Another specimen, called Prognathodon rapax was discovered in Fresno County to the south of us.

This Mosasaur is on display at the Royal Tyrrell Museum in Drumheller, Alberta

No one sells specimens or replicas of those exact species, so we purchased a related species that will get the point across. It's a skull of a Prognathodon stadtmani that was discovered in the Durango, Colorado region. It is a big skull! I can't imagine a child upon seeing this skull not wanting to get out and explore and maybe find one on their own. And knowing that it could actually happen because one like it was found in their own county. The dinosaurs were okay, they might think, but we had really interesting creatures that lived right here!

This is an exciting time for the children of our valley, even if they don't know it yet. They are about to discover a world, their world, that includes massive and sometimes ferocious creatures like the Mosasaurs, Ichthyosaurs, Plesiosaurs, Saber-tooth Cats, Short-faced Bears, Dire Wolves, American Lions, Megalodon sharks and many others.

Out of the Valley of Death: Home from the road

Dantes View at Death Valley National Park

It's geology in the starkest terms. Death Valley is a place where the crust has been torn asunder, with valley floors lying below sea level next to peaks that reach 11,000 feet. Rocks here are rarely hidden by vegetation or soil. It's a land alien enough that George Lucas filmed parts of Star Wars here. It's a land that crushed the dreams of many people, and provided sanctuary for others.

The rocks of Death Valley record an unusually complete history extending from the early Proterozoic eon as much as two billion years ago to rocks that formed only a few centuries ago. It's hard to imagine a better place for teaching geology, and that's what I was doing over the last couple of days.

I bet no one has ever thought of taking a picture from this particular spot before!

The students were enthusiastic and curious, the weather was outstanding, and the scenery was on a grand scale. We'll explore some of the fascinating corners of this incredible landscape in the next few posts.

Some of the oldest rocks in the American west, metamorphosed around 1.7 billion years ago.