Getting Under the Skin of a Volcano: Travels in Lava Beds National Monument

What in the world is going on here?? What are these spikes coming out of the ceiling? Is it some kind of deadly trap for Indiana Jones or Lara Croft? Well, no, but they'll hurt like the dickens if you try exploring them without a hardhat. In some of the previous posts in this short series we explored the deep heart of the magma chamber beneath a volcano, and we went both on and above Mt. Shasta to see the dramatic exterior of a volcano. Today we burrow under the skin of a volcano.

Medicine Lake Highland is the biggest volcano in California. It may be barely half as high as Mt. Shasta, but it makes up for the height deficit with broad gentle slopes, giving it a volume of around 130 cubic miles, compared to about 85 for Mt. Shasta. It is classed as a shield or "shield-type" volcano, composed largely of basalt, but with varying amounts of andesite and rhyolite. As such, it displays a wide variety of volcanic phenomena, not the least of which is a dizzying array of lava tubes. A flank of the volcano is preserved as Lava Beds National Monument, and the park has within its borders the highest concentration of lava tubes in the country, if not the world. More than 700 individual caves are known at Lava Beds with a total length of more than 70 miles.

How do lava tubes form? The picture above shows an active lava flow at Pu'u'o'o Crater on the Kilauea volcano on the Big Island of Hawai'i in 2009. The scale in this aerial view is difficult to discern but the skylight (where the red lava is visible) is probably 30 feet across. The tubes develop when river-like lava flows crust over. The lava continues to flow just beneath the surface, sometimes for many miles, being insulated by the overlying crust. The flow in the picture above flowed seven miles to the shoreline and was only a few tens of degrees cooler than it was when it emerged at the vent of Pu'u'o'o. When the eruption ends, the lava drains from the tubes.

The tubes can be quite complex, with bifurcating passageways and multiple levels (one particularly complex cave is called the Catacombs). During our recent visit at Lava Beds we explored Valentine Cave, one of the most accessible in the park. The majority of the tubes are in the Mammoth Crater flow which is around 30,000 years old. Valentine is in a younger flow, around 12,000 years old, so it has less collapse debris than many of the older caves (although it is true that many fallen boulders were removed by CCC workers during the Great Depression). In any case, the passages are easy to negotiate.

Being composed of very dark rock that tends to absorb light, tubes are notoriously hard to photograph. Flash photography tends to produce washed-out photos with little depth. I was using a bright flashlight for illumination and was holding it at arms length to get shadows that provide a sense of depth. I tried using my normal 'sophisticated' camera, but I actually got better results from my Samsung phone!

There are many interesting flow structures in the caves, including the pahoehoe flows on the floor of the caves, and "bathtub rings" on the walls showing that some flows only filled the cave a third full.

The basalt fractured as it cooled, forming the numerous cracks in the roof of the cave. Subsequent weathering in the soils above produced sodium bicarbonate and other chemicals that stain the edges of the fractures.

A lava cascade emerges from a side passage in Valentine Cave.

The lava tubes of Lava Beds National Monument are a fascinating environment to explore. Some of the caves have multiple levels, and some are decorated with permanent ice. One, Fern Cave, has numerous Native American pictographs and also ferns, which is interesting because ferns are not otherwise found in the park; they are a species of the western Cascades. The cool damp environment of the cave provided the right conditions for the plants, which may have arrived on birds feet (I'm guessing here).

There is a lot to do in Lava Beds. The ice cave and Fern Cave can only be visited with a ranger guide, but around twenty caves are open and developed for unaccompanied exploration. One, Mushpot Cave, is lit and has interpretive signs, and even a small amphitheater for ranger talks. On the surface there are lots of hiking trails that allow for the exploration of cinder cones, spatter cones, fault scarps, and the human history of the region (which will be covered in a separate post).

All in all, it's a good place to get under the skin of a volcano!

Want to See Some Incredible Volcanoes Up Close? Geology of California's Volcanoes, Sept. 27-Oct. 1, with Modesto Junior College

I write so much about my travels around the American West and elsewhere, and some might wonder where I find the time. Well...I tend to have a group of students with me. Geology, perhaps more than any other science, is best learned in the field, and our school recognizes the importance of field experiences. The community college system in California is of course one of the best alternatives for beginning a college education, a gateway to transferring into universities, but we also recognize lifelong learning as a part of our mission. Education doesn't just end with a degree. Professionals in one career can benefit from courses in related disciplines as a way of improving their job performance, or advancing up the pay scale. And all citizens can benefit from becoming better informed on the political issues of the day, such as climate change, or energy development (pulling some examples from geology).

With this in mind, I wanted to let my Modesto area-based readers know about some great field studies trips coming up this fall. On September 27-October 1, I'll be teaching Geology 185, the Geology of California's Volcanoes. We'll be exploring Mt. Shasta, Lava Beds National Monument, Medicine Lake Highland, and Lassen Volcanic National Park, as well as Castle Crags and McArthur-Burney Falls State Parks. We will be camping at Woodson Bridge State Park the first night, spend two nights at Lava Beds National Monument, and the last night at McArthur-Burney Falls State Park. There will be hiking and caving opportunities, and some simply incredible scenery among some of the youngest volcanic features in the western United States.

If this sounds intriguing, you can find more information at http://hayesg.faculty.mjc.edu/Cascades_field_studies.html. California residents pay the normal tuition rate (2 semester units), but the rate is higher for out of state participants. The $80 fee for the course covers the van transportation and fees at the various parks and campgrounds. The students provide their own food (we'll have stoves and fuel). For my local readers, we'll have an organizational meeting on Thursday, September 13 in the Science Community Center at Modesto Junior College, room 326, at 5:30 PM. Contact me if you have questions.

Airliner Chronicles: Do You Know California's Biggest Volcano? You May Be Surprised at the Answer

The summit complex of Medicine Lake Highland, with Glass Mountain at the top, the Medicine flow center-left, and Medicine Lake at center-right.

It's a real problem for a geologist to be flying through cloud cover. One loses track of time and location so when an opening in the clouds occurs, one cannot know for sure where one is. I can pick out the essential geologic details a lot of the time, but without temporal or spatial context, I can't recognize even some of the most familiar places that I've visited many times. That's what happened last Thursday when I was flying to SeaTac. I lost sight of the ground only a few minutes out of Sacramento, and when the ground reappeared again, I was totally fooled by the scenes in these pictures. I thought I might be over Newberry Crater in Oregon, but I couldn't place Paulina Lake with the steep ridge that should have been to the right in the picture above. So I figured it must be some place in the Three Sisters area that I wasn't familiar with. But then I got home and looked at the pictures on the computer instead of the camera. I was wrong.

The Medicine Flow dates to about 2,000 years ago. It is composed of thick dacite lava flows. Frozen Medicine Lake is to the right.

It turns out I was flying right over the top of California's biggest volcano. Mt. Shasta is California's most prominent volcano, rising to 14,162 feet above sea level. It's the largest stratovolcano in the entire Cascades chain, with more bulk than even Mt. Rainier, which we looked at in our previous post.

[At this point there is a bit of uncomfortable shuffling in the back of the room as a few of the geologists look at each other and start mumbling something unintelligible.

"Ahem, is there something you would like to add to the discussion?" I say.

"But we've seen Mt. Shasta, and it looks nothing like that".

"And you would be right" I say, "but give me a chance to finish". They relent.]

But this isn't Mt. Shasta. It may be the tallest volcano in California, and it may be the biggest stratovolcano in the Cascades, but we are forty miles northeast of Shasta, looking at an entirely different kind of volcano. It's a shield volcano called Medicine Lake Highland. Although it is not even 8,000 feet high, it is much wider, with a total volume of around 130 cubic miles, compared to about 108 cubic miles for Mt. Shasta.

The view from the ground shows a gently sloping edifice covered by a variety of cinder cones and plug domes. Medicine Lake Highland (MLH)is shield-shaped like the giant volcanoes that make up the Hawaiian Islands, and is composed in large part of basalt, the fairly non-viscous lava that can flow for long distances before congealing. But MLH is different in some important ways. Some of the magma chambers beneath the volcano originate in the crust rather than the mantle (dacite or rhyolite), and the silica-rich lavas that erupt at the surface are sticky and barely flow at all.

MLH is an active volcano. There have been at least 17 eruptions in the last 11,000 years, and the Glass Mountain flow (below) erupted only about 850 years ago. There are areas of geothermal activity that have been proposed for energy development, but these have been rebuffed so far (thank goodness).

Glass Mountain at the top of Medicine Lake Highland. The flow dates to 850-900 years before present.

The top of the shield complex is a caldera (a sunken crater-like depression caused by the inward collapse of the top of the volcano). It is about the size of the Crater Lake Caldera, but is not nearly as rugged, as it is many thousands of years older and has been partially filled with subsequent lava flows. Medicine Lake sits within the caldera, but is not volcanic in origin. During the ice ages, glaciers scoured the summit area of MLH and left behind some impermeable clay deposits that prevent water from sinking into the ground (there are very few streams or rivers on the volcano, as it is highly porous; massive springs are found around the base of the volcano.).

One of America's most interesting national monuments is found on the north flank of MLH. Lava Beds National Monument preserves more than 75 miles of underground lava tubes, one of the highest concentrations of such caves in North America (and maybe in the world). The park also preserves the memory of the last stand of the Modoc people in their struggle against the U.S. military in the 1870s. They held out for months in the barren lava flows but were finally betrayed and captured. The Modoc people survive, but much of their cultural history was lost when they were banished to Oklahoma.

The clouds soon closed in again and I saw nothing more until we were over Washington.

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.

The Lake at the End of the World: Tule Lake in Northern California

Tule Lake is situated at the end of the world. It's not that it's so big that the world seems to end beyond its margins, but something more like how it is the place that worlds ended. The lake is located in Northern California near the Oregon Border south of Klamath Falls. It fills a fault graben, a basin that formed when the crust stretched and cracked, with large valleys that sank hundreds or thousands of feet. The Tulelake graben sank enough to disrupt the flow of regional streams, and became a huge, but shallow lake. In this semiarid climate water is precious, especially to birds on the migratory flyway from the arctic to the tropics. It's one of the places where plentiful food allowed millions of birds to rest and fatten themselves to continue their journeys.

But it nearly ended for the birds. Settlers in the late 1800s found that streams could be diverted, and that levees and dikes could be constructed, so that vast portions of the lake dried up and disappeared. The nutrient rich sediments of the lakebed became pastures and rich soils for growing alfalfa or potatoes. In 1928, though, a wildlife refuge was established that preserves the remaining lake area for the birds and other animals. The present lake, as big as it seems in the photo above, is but 10% the area it once was.

The lake was the end of the world for a people as well. The Modoc people lived along the shores of the lake for hundreds, maybe thousands of years, but were forcibly removed in the 1870s. Many elements of their culture were lost as their community was shattered. I wrote more extensively on this sad history in a previous post. The story is compelling...check it out!

This is a dispatch from the road, some short descriptions of our ongoing field class on the geology of California's volcanoes.

About to Hit the Road Again! There are Volcanoes in my Future

And it's been way too long locked away in an office and laboratory and lecture hall. I'll be hitting the open road with my students on an exploration of California's Cascade volcanoes for the next five days. We'll be seeing Mt. Shasta, Lassen Peak, Medicine Lake Highland, and Lava Beds National Monument. All in all, it's a fascinating corner of the Golden State. I may actually have some web access along the way, so I'll try to send some dispatches.

You've Read About Them: How About Seeing Them in Person? California's Volcanoes Field Studies, Sept. 22-26, 2016

Mt. Shasta, the second tallest and most voluminous volcano in the Cascades

I write so much about my travels around the American West and elsewhere, and some might wonder where I find the time. Well...I tend to have a group of students with me. Geology, perhaps more than any other science, is best learned in the field, and our school recognizes the importance of field experiences.

Lava Beds National Monument

The community college system in California is of course one of the best alternatives for beginning a college education, a gateway to transferring into universities, but we also recognize lifelong learning as a part of our mission. Education doesn't just end with a degree. Professionals in one career can benefit from courses in related disciplines as a way of improving their job performance, or advancing up the pay scale. And all citizens can benefit from becoming better informed on the political issues of the day, such as climate change, or energy development (pulling some examples from geology).

Medicine Lake, glacio-volcanic lake occupying a large caldera.

With this in mind, I wanted to let my Modesto-based readers know about some great field studies trips coming up this fall. On September 22-26, I'll be teaching Geology 185, the Geology of California's Volcanoes. We'll be exploring Mt. Shasta, Lava Beds National Monument, Medicine Lake Highland, and Lassen Volcanic National Park, as well as Castle Crags and McArthur-Burney Falls State Parks. We will be camping at Woodson Bridge State Park the first night, spend two nights at Lava Beds National Monument, and the last night at McArthur-Burney Falls State Park. There will be hiking and caving opportunities, and some simply incredible scenery among some of the youngest volcanic features in the western United States.

Jot Dean Ice Cave. The ice persists in the cave year-round.

If this sounds intriguing, you can find more information at http://hayesg.faculty.mjc.edu/Cascades_field_studies.html. California residents pay the normal tuition rate (2 semester units), but the rate is higher for out of state participants. The $90 fee for the course covers the van transportation and fees at the various parks and campgrounds. The students provide their own food (we'll have stoves and fuel). For my local readers, we'll have an organizational meeting on Thursday, September 8 in the Science Community Center at Modesto Junior College, room 326, at 5:30 PM. Contact me if you have questions.

Lassen Peak and Manzanita Lake. Lassen erupted in 1914-15, while Manzanita Lake formed behind a debris avalanche about 300 years ago.

This isn't our only field studies opportunity! Watch for other announcements soon.

Yesterday's Mystery Rock Explained (Sort of...)

Yesterday's mystery rock was strange. Had I not been standing on the flanks of the largest volcano in California (and possibly in the lower 48 states), I would have guessed that the rock had been formed by boring (that's as in "digging", not "uninteresting") clams or some other creature. Many of you guessed the same, and I don't blame you at all.

The easy answer, the quickest explanation is to say that this is the surface of a boulder of vesicular basalt, the term "vesicular" referring to the presence of gas bubbles that formed during the extrusion of  lava on the Earth's surface. The boulder was being used as a vehicle barrier at the pullout for the Devil's Homestead lava flow at Lava Beds National Monument. The monument covers a portion of the northern flank of Medicine Lake Highland, a huge volcanic shield complex along the boundary between the Cascade Range and the Modoc Plateau.

The thing is, I've never seen vesicles like this before. They are uniform in size and spacing. They also looked very strange from the side: they were the top of linear tubes running through the rock. I'm not even sure the tubes and vesicles are right side up. The rock had been moved into the parking area, after all, and could have been overturned in the process.

I find references to "pipe vesicles" that form when lava flows over sources of water (the pockets of steam rise through the lava), but I'm not knowledgeable enough on the subject to say that the term applies here. If the volcanologists among you want chime in, I am all ears!

Thanks for the many responses. I love a good mystery!

Exploring the Southern Cascade Range or Yosemite National Park for College Credit! Sept. 24-28 and Oct. 9-11

Captain Jack's Stronghold, where the Modoc people held out for months against U.S. troops. The site is protected today as Lava Beds National Monument.

This message is primarily for my readers in the Modesto region, but others are invited to consider this opportunity. Modesto Junior College has an active geology field studies program that offers the chance to explore some of the best geology on the planet, in the mountains and deserts of California and other parts of the American West. The courses provide valuable field experience for geology majors and teachers of earth science, and can provide rich life experiences for people who are casually interested in geology. We have a bit of room if you wish to join us!

The opening of Skull Cave, the largest lava tube entrance in Lava Beds National Monument.

We are offering two extended overnight trips this semester. On September 24-28, we will explore the geology of California's volcanoes (Geology 185; 2 semester units), and on October 9-11, we spend three days in and around Yosemite National Park (Geology 180; 1 semester unit). Both trips involve camping out in sometimes rugged conditions, using vans supplied by the department. The cost includes the per-unit registration fee, and an additional $90 for Geology 185, and $45 for Geology 180.

Valentine Cave in Lava Beds National Monument

The trip for Geology of California's Volcanoes will include stops at Castle Crags State Park in the Klamath Mountains, Mt. Shasta (including a drive to the end of the road at 8,000 feet), Lava Beds National Monument, Medicine Lake Highland (the biggest but not highest volcano in California), and Lassen Volcanic National Park. Some challenging hikes (and cave explorations) will be offered, but not required. One will be able to complete the course without great physical exertion, although one should be in reasonably good health to be out there traveling and camping.

McArthur-Burney Falls in the Cascade Range

The Geology 180 course, Geology of the Central Sierra Nevada, will explore all of the accessible parts of Yosemite National Park, including Yosemite Valley, Tuolumne Meadows, Glacier Point, and possibly Hetch Hetchy. We will be camping at Wawona and Crane Flat during the trip.

Lassen Peak is the most recent volcano to erupt in California, in 1914-15.

If you are in the Modesto area, we are having an organizational meeting for both of the trips on Thursday, Sept. 17 at 5:30 PM in Science Community Center 326 on the West Campus of MJC. If you can't make the meeting, contact me (hayesg(at)yosemite.edu). More information can be found at http://hayesg.faculty.mjc.edu/Cascades_field_studies.html and http://hayesg.faculty.mjc.edu/Yosemite_3_day.html. Several day trips will be offered later on in the semester, to the Mother Lode (if it hasn't burned completely up), and to Pinnacles National Park and the San Andreas fault.