A California Love Letter: It's the Best Geology to be Found Anywhere!

This is the second of some resource materials I have on our college website that are being removed, so I wanted to preserve them. The following is some info I give to my students of my "Geology of California" course. For the majority of these students, it is their first introduction to geology, and their first introduction to the extraordinary state that is their home. For a more complete explanation of each superlative, click on the orange links (down the rabbit hole!). Enjoy!

Highest point in the lower 48 states: Mt. Whitney, 14,505 feet 

Lowest point in the western hemisphere: near Badwater, Death Valley, -282 feet

The deepest canyon in North America (maybe): Kings Canyon, Giant Sequoia National Monument. Hells Canyon on the Oregon/Idaho border may be 19 feet deeper. Maybe...

Largest living things in the world: Sequoia Trees

Tallest living things in the world: Coast Redwoods

Oldest living things in the world: Bristlecone Pines (5,000 years), White Mtns, or Creosote Bushes in Colorado Desert (11,000 years)

My Scottish BBC Interview at a relatively balmy 110 degrees

Hottest Place on the Planet and Driest Place in North America: Death Valley: 134 degrees, precipitation 1.4"/year

One of the Snowiest Places in the U.S.: Tamarack, Sierra Nevada, 76 feet in one year, 32 feet in one month, 37 feet on ground at one time

Highest Waterfall in the North America (no. 7 in world): Yosemite Falls, 2,425 feet

Second tallest active volcano in the U.S.: Mt. Shasta, 14,162 feet

Second most recently active volcano in lower 48 states: Mt. Lassen (1914-21)

Most voluminous volcano in the lower 48 states: Medicine Lake Highland (around 130 cubic miles) in northeastern California

Scarp from the 1872 Lone Pine earthquake

Some of the largest earthquakes in the lower 48 states: 1906 (San Francisco 7.8), 1872 Lone Pine (7.8), 1857 (Ft. Tejon 7.8)

Old oil derrick near the Santa Clarita Valley

One of the more prolific oil and natural gas producing regions in the world: Los Angeles Basin, Bakersfield, and Santa Barbara-Ventura Channel

One of the biggest explosions ever: Long Valley Caldera, 750,000 years ago, 125 cubic miles of ash spread all over the western states as far east as Nebraska and Kansas

McWay Falls at Julia Pfeiffer-Burns State Park on the Big Sur Coast

No other state has the combination of landscapes: Coastlines, deserts, mountains, river valleys and plateaus, due in no small part to the fact that California is influenced by all three different kinds of plate margins: Divergent, convergent and transform. Few places in the world have this kind of diversity.

The San Andreas fault on the San Francisco Peninsula. San Andreas reservoir, from which the fault took its name, is in the foreground.

What would you add to this list???

Stuck Between a Volcano and a Hard Place (part 2): Politics and Geology Square Off in a Small Town with a Big Problem

I've been more and more concerned about the public damage being done to the scientific community and larger society as politics has swirled like a tornado around global warming, climate change, and pandemics. Trust is eroding in some quarters, and I only see this leading to worse disasters in the years to come (and really, nearly a million Americans dead is a huge disaster, even though it unfolded slowly over two years; just imagine the impact if those people had died all on one day). This damaged social compact between those who do science and the society at large reminded me that it isn't the first time this kind of issue has affected the public, and a few years ago I wrote about it in a two-part series. Here, with some modifications and updates, is part two.

Twin Lakes, above the town of Mammoth Lakes on the edge of the Long Valley Caldera

So what happened in Mammoth Lakes?

In the last post we talked about the titanic explosion at the Long Valley Caldera 760,000 years and tried to comprehend the scale of an event where 150 cubic miles of ash was blown into the atmosphere, covering much of the country. We then fast-forwarded to the near-present day of Mammoth Lakes in the 1980s. When we left the story, geologists were trying to decide what to do at the ski resort town in the face of astounding earthquake swarms, ground level changes, and increased geothermal activity.

It could probably be called a (tragi)comedy of errors. The USGS volcanologists carefully prepared a report to accompany a NOTICE OF POTENTIAL VOLCANIC HAZARD, the lowest level warning in their guidelines. A reporter from the Los Angeles Times figured out what was going on and published a story about the potential volcanic activity the day before the USGS released their report. The geologists got scooped, in other words, and the story became a runaway train in the national media. The government and emergency services personnel who were supposed to get the report and develop a response plan were blindsided by reporters asking them how it felt to be living in a doomed town.

The carefully worded statement from the USGS noted that "available evidence is insufficient to suggest that a hazardous event is imminent", but it was their description of the hazards that caught the attention of reporters and news hosts: rocks falling out of the sky miles from the eruptive vents, hot ash flows melting thick snowpacks and producing dangerous mudflows, and dangerous gases suffocating people. The very manna of the most desired headline: if it bleeds, it leads.

Hot Creek, a geothermal site in the Long Valley Caldera

By some accounts, the damage to the economy of Mammoth Lakes from the media circus may have been worse than an actual volcanic eruption (though no one died). Tourists stayed away in droves, businesses went belly up, and condo projects were abandoned. The business leaders of the town were livid at the geologists for stirring things up and scaring people (although by my reading, their notices were very conservative and carefully worded). They demanded that the geologists stop their campaign of terror/error, accusing them of bad science or something darker. There were even bomb threats (I had forgotten that detail; see the reference at the end of this post).

Warning sign at Horseshoe Lake, one of the carbon dioxide tree-kill sites on Mammoth Mountain.

The geologists could only respond in disbelief. I feel like I would have said something along the lines of "You are sitting on top of an active body of magma that is a few thousand feet from the surface! It would be irresponsible to keep such a thing secret". The geologists stuck to their guns, and the threat level remained at level one, the lowest level of concern, but concern nonetheless.

The business owners and local politicians went up the chain of command. They appealed to the head of the USGS, and his boss, the Secretary of the Interior, a man named James Watt. They may have communicated with then-president Reagan. As far as I can tell, there was intense political pressure from above, and eventually the director of the USGS unilaterally scrapped the warning system. Poof! It was gone. No discussion. It its place would be an informal warning system of quiet communications between geologists and civic leaders.

If this were a Hollywood movie, what happens next would be preordained. Everyone would come back. The skiers would be happily sliding down the slopes, businesses would be taking in money hand over fist, and suddenly out of nowhere there would be a resounding explosion and all hell would break loose as the caldera gives way to a catastrophic eruption that kills the "evil" business leaders because they had been greedy, and a gritty, yet handsome geologist would lead a beautiful woman and her plucky children to safety. Heck, I could see casting someone like, oh, say, Pierce Brosnan as the geologist and Linda Hamilton as the lady. Maybe call it "Dante's Peak" and move the setting to Idaho for some reason.

Yeah, I'd say that casting choice for the geologist was about right. Either one of them....

But that isn't what happened, of course. The molten magma was almost certainly there, but it cooled and solidified instead of continuing to the surface. The earthquake swarms ebbed, but other swarms have taken place over the years, though most have been tectonic in origin (related to faulting rather than magma). Gases from the magma chamber, especially carbon dioxide, have continued to seep from the ground, killing trees and other vegetation in several areas, including Horseshoe Lake (below). The gases actually killed three people a few years ago.  After some years, the USGS established a volcano observatory that monitors Long Valley, and came up with a new warning system, one with four stages, and specific actions to be taken with each. It's based on colors, just like our former Bush-era terrorism warning system. The town's economy slowly recovered. They started building condos again.

Tree kill area at Horseshoe Lake. Carbon dioxide in the soil suffocates the roots and microorganisms necessary for the tree's survival

Some of the political leaders took a bit of action. One of the main concerns was that an eruption would have destroyed the only paved road out of town. No evacuation would have been possible if the highway was blocked off. A few years after the brouhaha, a road appeared at the upper end of town called the Mammoth Lakes Scenic Route. I have to say that as a geologist that I didn't see a whole lot of scenery as I drove this nice paved highway, but I couldn't help but notice that it was exactly where I would have chosen to put an evacuation route (according to Dick Thompson in Volcano Cowboys, the county supervisors responsible were recalled from office for arranging this bit of road-building; it was like an admission that volcanism was actually possible).

Hot Creek, one of the centers of geothermal activity within the Long Valley Caldera.

In the end, one can only say mistakes were made. Some of those mistakes involved a sort of public relations tone deafness, like releasing a volcano warning on the eve of a holiday weekend, but other mistakes were more nefarious.

There were people willing to deny the possibility of a natural catastrophe in order to protect their profit margins. I see too many parallels in today's political (but not scientific) debates over global warming and climate change, and in the willful denial of the Covid pandemic. The geologists had clear evidence of a volcanic threat and the civic response was to deny the evidence and to attack the reputation of the geologists who were trying to do the right thing. There was a threat to the economy of Mammoth Lakes, but the threat was from a geologic process, not those who discovered and analyzed the volcanic hazard. And threatening the lives of the geologists was criminal. And apparently unpunished.

And the media. What to do about the media? Isn't it amazing how media outlets were willing to blow a story way out of proportion in order to gain ratings? Isn't it nice to know that they don't do that sort of thing anymore? And that the internet (which didn't exist as such in 1983) has turned out to be the very model of accurate and measured analysis of stories like this one, despite the possible instant dissemination of incorrect and potentially dangerous information? I'm so glad we live in an age of logic and reason and respect of scientific research.

Oh, I'm sorry. I briefly stepped into "Opposite-world". I'm back now. Science education and science literacy have never been more important in a world where the internet and media are so irresponsible with their analysis of geological hazards. Every time there is another major earthquake or volcanic eruption, I feel like throwing a shoe through the television screen or computer monitor as the talking heads begin babbling. Instead, I do what I can by throwing words out into the internet trying to offer up a more measured explanation of things. But the mostly ignorant talking heads always seem to win people's attention.

Just imagine the outcome if the geologists at Mammoth Lakes were effectively squelched, no warnings were ever given, and a volcanic eruption had actually occurred. Beyond the devastation, just imagine the scapegoating that would have happened in the aftermath. In Italy such a situation led to prison terms for half a dozen geologists who failed to predict a deadly earthquake (they have since been released).

We can do better than this. Especially those in the news business who are responsible in times of emergency for providing us with reasoned assessments, not sensationalist drabble. When the crisis is over, they can go back to their manic headlines about the personal lives of the stars.

You can read the original post from 2015 here: https://geotripper.blogspot.com/2015/02/the-sierra-beyond-yosemite-politics-and.html

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Although aspects of this story of the events at Mammoth Lakes and the Long Valley Caldera are drawn from my memory, I reviewed and confirmed many of the details in the excellent book called "The Volcano Cowboys: the Rocky Evolution of a Dangerous Science" by Dick Thompson (St. Martin's Press, 2002). Check it out, it's a fascinating account of the lives and activities of volcanologists.

Geotripping! It Could Be You! Geology of the Eastern Sierra Nevada, September 26-30

The east side of the Sierra Nevada and the adjacent Owen's Valley is one of the most dramatic landscapes on planet Earth. The valley that forms the eastern boundary of the range is two miles deep, twice the depth of the Grand Canyon. The valley contains active faults (responsible for one of California's most powerful earthquakes ever, the 1872 Lone Pine quake), and active volcanoes, ranging from small cinder cones to gigantic calderas that rival those of Yellowstone.

The region is full of fascinating geological features, including Bodie, one of the most well-preserved ghost towns in the American west. There is also the nation's "Dead Sea" which is not really dead at all, preserving the lives of millions of migratory birds. Mono Lake is the epicenter of the LA water wars, an issue that can only become more important as California enters a new and unprecedented climate regime.

Scenery abounds, and tourists and explorers love this region like few others. But how often have people traveled through this region without the awareness of the incredible geology exposed at their feet? Are you one of them? Have you never had the privilege of exploring this incredible landscape? Well, I've got a great opportunity for you...

On September 26-30, the Geology Department at Modesto Junior College will be offering Geology 186, a 2-unit field course on the geology of the eastern Sierra Nevada and the Owen's Valley. We'll leave the college early Thursday afternoon and drive to our expected first night stop at Baker Station, the High Sierra Institute, located in the high country of the Sierra near Sonora Pass. The facility is run by our district for a variety of multidisciplinary classes.

From there we'll cross the Sierra Nevada at Sonora Pass and explore the lands to the east, including Bodie and Mono Lake before arriving at our base camp at Millpond Recreation Area just outside of Bishop in the Owens Valley. We'll spend three days there. We'll check out the Long Valley Caldera, the Volcanic Tableland, Devil's Postpile, Inyo Craters, and Minaret Summit the next day.

The following day we'll head up into the White Mountains across the Owens Valley from the Sierra Nevada, where we'll have a bird's-eye view of some of California's remaining glaciers, and have a look at the oldest trees on the planet. We'll then head south to Lone Pine and Owens Lake.

Our final day we'll head back up through the caldera with a stop at Convict Lake (below) and then make our way home via Tioga Pass and Yosemite National Park.

We'll be camping out, and you'll be your own cook on this trip. We'll travel in school vans. The trip will cost $80 plus the cost of tuition at MJC (about $100 or so). Information can be found at http://hayesg.faculty.mjc.edu/Eastern%20Sierra%20Nevada.html, and the MJC website (to enroll in the class) can be found at https://mjc.edu/. If you live in the Modesto area, we'll have an organizational meeting on Thursday, September 12 at 5:30 PM in the Geology Lab at MJC, Science Community Center 326. If you live outside the area, I can send you the relevant materials.

The Sierra Nevada and Owens Valley is an incredible place to explore. I hope you'll be joining us!

Looking Back at Ten Years of Geotripping: "They're, uh...They're Not a Very Exciting People, Those Geologists"

I borrowed the quote in the title from a Cracked.com article (referenced below) as a starting point to some musings about the adventures in life that are possible for people who don't happen to be astronauts or Himalayan mountain-climbers. If there is any theme that has run through my ten years as a geoblogger, it is about the adventures that geologists and geo-fans get to have as a result of having that bit of extra geo-knowledge about the regions and landscapes they see and live in. I've been digging up the archives, and this was one of my favorite posts in 2011...

From May 9, 2011:

What does "adventure" mean to you?

This is an adrenaline rush...

I suppose that an adventure is just about anything that breaks up the routine and exposes you to something new. For a lot of people I am guessing that adventure has a lot to do with an adrenaline rush: I think of motorcycling, rock-climbing, bungee-jumping or rides at an amusement park.

Others may think of adventure as exploration to the outer edges of space, beyond the reach of civilization, of the deep sea, the kinds of adventures that we might read about in National Geographic or history books. But how many people actually participate in that kind of adventure?

Other adventures come out of mythology; the quest, the dangerous journey with an uncertain outcome. We don't see so many of those, but I wonder if a mythological narrative will arise from recent events concerning Osama Bin Laden and those who sought to capture or kill him.

We live most of our adventures through the lives of someone else, in books and movies and so on. The vast majority of us just don't have the resources, or time, or health to be out on the cutting edge of human experience. It's for that reason that I want to talk about learning about geology as an adventure, in all of the best ways and something that almost anyone can do in some way. I think I started musing on this topic because of a cute item from Cracked.com. They do some hilarious stuff, but the last line of this post was, eh, whatever...

"They're, uh ... they're not a very exciting people, those geologists."

I grant you that I am not a very exciting person, in person. But I wouldn't trade my life as a geologist and teacher with anyone. What makes geology such an adventure? I can think of many examples, and here are a few:

Geologic hazards like volcanic eruptions and earthquakes have been fodder for movies and novels for decades. Geologists actually get to study these things as a part of their career. What a thrill to work on the flanks of an active volcano, monitoring and predicting future activity. There is certainly an adrenaline rush when standing next to flowing lava! A nice bonus? They sometimes save lives with their research. The story of the 1991 eruption of Pinatubo in the Phillippines is a nice example. The eruption was the second largest event of the 20th century, and killed some 800 people. On the other hand, tens of thousands of lives were saved because of a timely warning to evacuate the region. This is all the more remarkable considering that during the height of the eruption, a typhoon swept into the island (it was actually the cause of the majority of fatalities). Even bad screenwriters and novelists don't even think to throw typhoons on top of volcanic eruptions!

Have you ever wanted to be on an adventure to find buried treasure? Geologists and rockhounders alike know the thrill of uncovering a rare crystal. It's hard to be in the field all the time without finding the occasional opportunity to search for quartz, garnet, topaz, or any other number of beautiful expressions of atomic-level symmetry. It's the rare geologist who doesn't have a small treasure trove of gemstones (or here) on a mantle or bookcase shelf.

What about that childhood dream of finding a dinosaur? There is nothing quite like uncovering the bones of a creature that lived more than 65 million years ago. If you spend enough time in the right regions of the world, and you have enough geological background to know the age and nature of the rocks you are exploring, you can know that thrill (I'm not talking about a college education; there are geo-guides for the layperson that are full of accessible info about every region of the countryside). It's happened to my students (and myself) a fair number of times over the years. And there's no feeling quite like it. I was whooping like a kid (and promptly called the Utah Geological Survey; there's a right way to do these things).
Did you ever imagine owning a time machine, of traveling back in time? An understanding of the basic principles of geology is the tool geologists use to time-travel. It's effective; a bit of knowledge, and you can lay your hand on the surface that reveals incredible moments in the history of the world. In the picture below, I have my hand on the moment that the dinosaurs went extinct (via one of the most likely hypotheses). It is the iridium layer at Gubbio, Italy, where the Alvarez father and son team discovered evidence of a massive asteroid impact.
In the other photo, we are looking at the moment that the Long Valley Caldera erupted at the north end of the Owens Valley in the Eastern Sierra around 790,000 years ago. More than 125 cubic miles of hot rhyolite ash filled the atmosphere and blanketed the region many feet deep, killing all living things. Do you need a movie to imagine cataclysmic events? It's a whole new experience to lay your hands on the moment that such events actually happened.
A basic understanding of geology enriches one's life. National Parks are nice places to see scenery. A place like Yellowstone is interesting because you see bison and geysers. It is fascinating when you come to understand the nature of the "supervolcano" caldera eruption that produced the rocks and the active magma chamber that causes the geothermal activity. A visit to Yosemite is always nice, but it takes on a whole new dimension when you realize you are walking about inside an ancient volcanic complex not unlike Yellowstone's. You are exploring the underside of a volcano!

During your travels this summer, stop by the visitor center and pick up a "Geology of..." book and read it. It can enrich your experience, and turn a vacation into a real adventure! Or, if you are in the Modesto region, consider taking a summer field study class in geology or archaeology at MJC (more on this soon!).

A Landscape as Bizarre as They Come: The Volcanic Tableland of the Eastern Sierra Nevada

The Volcanic Tableland, with the White Mountains beyond.

There is a bizarre landscape on the far side of the Sierra Nevada between Bishop and Mammoth Lakes. It's not one of stark beauty exactly, it's barren and covered by little more than sagebrush. It's got few roads or trails, primarily because very little of this landscape is of much use to anybody. From above, the surface is riddled with scarps and grabens from numerous faults. This is a broken-up land. It's not...normal.

Source: US Geological Survey

The surface of this landscape isn't "right" either. There are no dark rich soils here. The underlying rock is pink or white, and so is the weathered soil and debris that covers it. Although the surface has an area of several hundred square miles or more, the underlying rock is remarkably uniform. It is a volcanic rock called rhyolite tuff. And with that name, the explanation for this landscape is revealed: it is the remnant of an ancient disaster beyond imagining.

767,000 years ago, an explosion took about 125 cubic miles of pasty magma from the crust and blew it into the atmosphere. The huge void collapsed inwards, forming an oval-shaped depression 20 miles long, 10 miles wide, and a mile or more in depth. The resulting ash spread far and wide, blanketing the western United States. Measureable deposits can be found in Kansas and Nebraska. But most of the ash came straight down. Some of it refilled the caldera, but much of the remainder buried the regional landscape hundreds of feet deep in hot ash. All life would have been extinguished for miles in every direction.

It is difficult to understand the magnitude of such events. From a human perspective, we have nothing to compare it to. An eruption at Tambora in Indonesia in 1815 produced less than a tenth of the ash as Long Valley, and that was enough to cause global cooling with related summer snowfall, crop failures, and famine across the northern hemisphere. The effects of an eruption the size of Long Valley on modern civilization would be appalling. I've heard it said that modern agricultural production has a month-long lead on consumption demand (No, I can't cite a source. It's a factoid I'm sure I heard or read somewhere). Try to imagine a disruption of agricultural production lasting several years. Governmental and societal structures would collapse, and the death toll would be unimaginable. Humans would no doubt survive, but it would be a dystopian landscape as bad as any sci-fi action movie, and maybe worse.

The only good thing that I can think of to say on this possibility is that studies of calderas like Long Valley or Yellowstone suggest that the eruptions will be predictable on a scale of decades or centuries. There would be time to prepare the eruption, or, however unlikely, geo-engineer the caldera to lessen the intensity and effect of the cataclysm.

What happens when a singular event completely reshapes a landscape? The eruption of Long Valley completely disrupted the drainage patterns of the eastern Sierra Nevada and Owens Valley. The land had to start over. Where there had once been river valleys and canyons, there was now a gaping pit miles wide and long. The evidence suggests that for 600,000 years the caldera depression contained a huge lake similar in plan if not in scale to Crater Lake. Crater Lake has no outlet, with the lake level determined by evaporation and seepage. The Long Valley Lake would have been similar, as no evidence exists for an outlet, at least until around 150,000 years ago.

Source: U.S. Geological Survey

For 600,000 years sediment washed into the basin, slowly filling it. Finally, along the south rim of the caldera near the present day site of Crowley Lake, the basin spilled over. In just 150,000-160,000 years, the Owens River carved a 400-500 foot deep gorge down the surface of the Volcanic Tableland, laying bare the full extent and history of the climactic eruption of the caldera. The rate averages out to about a foot every 400 years, but the rate was probably higher at the beginning. The small creek that flows through the gorge today is a mere shadow of its former self. The Los Angeles Department of Water and Power has co-opted most of the water, but a court order several years ago mandated that a minimum flow must be maintained.

Because the LADWP has utilized the water from the Mono Lake Basin to the north, they have constructed penstocks and pipelines that allow them to produce energy as they transport water down the long slope of the Tablelands. That means access roads, and it is thus easy to visit the gorge, and it is fascinating.

The mounds seen occasionally along the rim are the eroded remnants of fumaroles, where steam would have emanated from the interior of the ashflow, leaving mineral deposits that toughened the rock. The tuff at the rim is relatively soft, but as one walks deeper into the gorge, the rock becomes harder (it tuffons up?). When the hot ash landed, it was hot enough to remelt, forming welded tuff, or ignimbrite. Pieces of pumice caught up in the eruption became flattened and smeared in places.

As the rock cooled, it contracted to form columnar joints. Unlike Devils Postpile, a few miles away on the other side of the crest of the Sierra Nevada, these columns are not vertical. Most columnar jointing is not. The intense fracturing of the rock into these columns aided the Owens River in the carving of the gorge, as the crumbling rock could be quarried by the rushing water much more readily than solid rock.

The columns average six sides, but columns with 4, 5, or 7 sides are occasionally seen.

The Volcanic Tableland and the Owens Gorge are otherworldly, but they provide a hint of how quickly landscapes can adjust to new geological conditions. It took 600,000 years to fill a basin 10 by 20 miles with at least 2,000 feet of sediment, and 150,000 years to carve a 400 foot deep gorge. This is fast by geologic standards, but humans, had they been around this region at the time, would not have noticed much change in course of their lifetimes. Just like we aren't noticing the changes now...

California's (not) Biggest, (not) Most Recently Active, and (not) Most Dangerous Volcano

Photo by Mrs. Geotripper

Mt. Shasta is no doubt the most dominating volcano in all of California. It's huge, topping out at well above 14,000 feet, and is visible from over a hundred miles in a number of directions. It was the first main stop on our recent journey exploring the Pacific Northwest and Northern Rocky Mountains, and it really stood out as we essentially circled it on our way to Lava Beds National Monument.

It's big, it's active, and it's potentially destructive. So how bad could it be? Is Shasta the biggest, most recently active and most dangerous volcano in the state? Actually...no. California has a great many volcanic features, and even though some are not as familiar to many of us, they do actually present a hazard for a great many more people than you might suspect. That's not to say that Shasta is not dangerous, however.

Castle Crags in the Klamath Mountains of northern California (photo by Mrs. Geotripper)

As Interstate 5 winds northward into the Klamath Mountains north of Redding, Shasta occasionally peeks out between the trees (the top picture), but for a brief moment near Dunsmuir a totally different set of mountain spires appear off to the west. They are the Castle Crags, a granite stock (an intrusive body of granite exposed over an area of less than 40 square miles; batholiths are larger).

Castle Crags (seen below in a picture from a plane flight a few years back) were relevant to our explorations because they represent a volcano from inside out. About 160 million years ago, the land surface was five or six miles above, and molten magma was moving up through the crust. Some of the magma reached the surface to flow in volcanic eruptions, building up volcanoes maybe similar to Shasta and others of the Cascades. The rest of the molten rock cooled slowly for tens of thousands of years, forming the crystalline granitic rock exposed today at the Crags.

Moments later, we made the imaginary journey up through the crust and onto the flanks of the modern volcanic edifice of Mt. Shasta. We followed the Everitt Highway up the mountain to the about the 7,500 foot level to have a look around. Even though we were on the first day of a crippling heat wave in California, the air was cool, and the snowbanks made it clear that winter was not yet entirely over.

Bunny Flats was the end of the road for us on this particular day. The last two or three miles of pavement above were covered by snow. The road used to end at a ski area, but the resort was closed years ago, due to avalanche danger (as I understand it; there is a newer resort on the lower slopes of the volcano). Working and playing on the slopes of a volcano does have its hazards...

There are a lot of hazards around Shasta. Lava flows might seem to be one of them, but andesite lava tends to be sluggish and slow. Lava doesn't worry me so much. Ash eruptions are certainly a danger, due to their speed and mobility. Shasta has had such eruptions, but they haven't been the usual modus operandi over the years. But...lava or ash flowing onto thick snow: that's a problem. The melting snow and debris quickly turns into a mudflow that can travel for tens of miles at high rates of speed. The Indonesians called them lahars, and the name has stuck. Most of the lower flanks of Shasta are mantled with lahar deposits, and the towns of Weed and Shasta City are built on them. Mudflows have even happened when there have been no eruptions. Meltwater can build up under the glaciers that cover much of the mountain and burst out with no warning (Icelanders call these glacial bursts jökulhlaups). All in all, it's a pretty dangerous volcano.

And it's active. There have been a number of eruptions in the last 10,000 years, including those that built up Shastina and Black Butte. The entire upper part of Shasta, the Hotlum Cone, is less than 9,000 years old. The volcano may have erupted in 1786. So is it the most recently active volcano in California? Nope.

From our vantage point at Bunny Flat, we had an unobstructed view southeast towards Lassen Peak and Brokeoff Mountain. Lassen is the winner of the "most recently active" designation. The plug dome began making noise in 1914, and let loose in 1915 with a lava flow, a destructive lahar, and an ash eruption that interrupted train service out in Winnemucca, Nevada. The eruption produced a mushroom cloud five or six miles high. Geothermal activity continues today in what is now Lassen Volcanic National Park.

Lassen Peak (left) and Brokeoff Mountain (right) from Bunny Flat

So what about the biggest? Surely a mountain 14,000 feet tall is the biggest volcano in the state of California? Well, it's certainly the tallest, and it is the most voluminous stratovolcano in the Cascades, but it actually isn't the biggest volcano in the state. When we camped that evening, we were ensconced on the flank of a massive shield volcano called Medicine Lake Highland. With the gentle slopes composed of basalt lava flows, it hardly looks like a volcano at all, but when you compare the width of the volcano in the picture below (it takes up three quarters of the skyline), you realize it is really big. It consists of around 130 cubic miles of lava, compared to about 108 for Mt. Shasta (which is the snow-capped peak on the right).

So it's the most dangerous, right?

Well...that's a hard concept to quantify. There are lots of volcanoes in California, and some are closer to population centers than others, and some are more capable of chaos and violence than others. The Clear Lake Volcanic Field, north of the Bay Area, has been active as recently as 10,000 years ago, and the Geysers Geothermal Area nearby shows that magma is still present at a relatively shallow depth. Several thousand people live in the general vicinity.

The Lassen Volcanic Center is an obvious threat, given the activity in 1914-17. There are only a few small villages in the immediate vicinity of the volcano, but it is a major tourist destination in the summer season. Lahars could presumably reach the Sacramento Valley.

The aforementioned Medicine Lake Highland is certainly still active, with eruptions as recently as 950 years ago. Although basaltic shields aren't known for violent eruptions, the presence of rhyolite plug domes around the summit area show that such eruptions are not out of the question. Like the others, the region is lightly populated.

Volcanism is also a possibility in Southern California, perhaps to the surprise of some. Young cinder cones dot parts of the Mojave Desert (the Lavic Lake Volcanic Center), and the Coachella Valley (the Salton Buttes). Some of the small volcanic cones are younger than 2,000 years old.

The "elephant in the room" in terms of volcanic hazards of California has to be the Long Valley Caldera, and the nearby Inyo-Mono Craters. Every time there is a jiggle on a seismometer in Yellowstone National Park the internet lights up with predictions of death and destruction, but the conspiracy nuts pretty much totally ignore California's version of a death volcano. An eruption that took place 760,000 years ago produced 125 cubic miles of ash that covered most of the American West (the three Yellowstone eruptions ranged from 67 to 600 cubic miles). Yellowstone has not had a volcanic eruption in 70,000 years. The volcanoes in the Long Valley area of California have erupted as recently as 300 years ago. No one is talking about a repeat of the catastrophe of the 760,000 years ago, but smaller eruptions could certain cause havoc in this very popular tourist area. There was a huge brouhaha in the 1980s that had a lot of implications for how public officials respond to potential geological disasters. I wrote an extensive blog post about the event a couple of years ago; you can read it here (it's one of my favorites).

So Mt. Shasta isn't the biggest volcano in the state, isn't the most recently active, and may or may not be the most dangerous. But does that mean we can disregard the volcano? Hardly. It could cause all kinds of mayhem in the wrong circumstances. And there is one more hazard here that is unique.

The area north of Mt. Shasta is a landscape characterized by a strange hummocky surface composed of volcanic rock, but the hummocks don't look like cinder cones or other volcanic features. Geologists didn't know what to make of this weird topography. Until Mt. St. Helens exploded on May 18th, 1980, that is. One of the most astounding events of that eruption was the collapse of the entire flank of the mountain into a debris avalanche that traveled for twelve miles down the Toutle River. It turned out that an ancient iteration of Mt. Shasta had a similar fate around 300,000 years ago, with a debris avalanche that traveled 28 miles, almost to the present location of the town of Yreka.

The debris avalanche on the north flank of Mt. Shasta. Shasta Lake, a reservoir, is on the left within the debris field (photo by Geotripper)..

It is hard to imagine events on this scale, but the geological world is full of events that challenge our perception. That was one of our themes as we set out on our two week journey, and it was only our first day on the road.