In the Heart of the Devil: The Damning of Del Puerto Canyon

This beautiful canyon is under serious threat

California geology is complicated. Unlike any other state, it is affected by the interactions of all three kinds of plate boundaries: divergent (the crust pulling apart), convergent (the crust compressing together), and transform (the crust sliding laterally). All of these forces have formed a complex landscape with incredible scenery unlike any other place in the world. 

The Coast Ranges province is one of those unique regions. Extending some 400 miles from the Oregon border to the Transverse Ranges near Point Conception, it is one of the least familiar parts of California (aside from the Pacific Highway 1 corridor through Big Sur and the Marin Headlands/Point Reyes region). The province is defined by a series of individual mountain ranges that trend roughly parallel to the coast, but the variation in rock types and structure is astounding. Within the province there are active volcanic fields, older inactive volcanoes, vast tracts of tilted sedimentary rocks, exposures of twisted and folded rocks formed deep within subduction zone complexes, and even a displaced section of Sierra Nevada granitic crust. Numerous active faults slice through the province, including many of California's most dangerous: the San Andreas, the Hayward, the Calaveras, and many others.

We just explored the heart of the devil: the so-called Diablo Range. It is one of the largest individual ranges in the province, running for around 150 miles from Mt. Diablo and the Carquinez Strait on the north to the Coalinga area in the south. The region is largely undeveloped, and few paved roads cross range. We followed one of those few roads, the one that traverses Del Puerto Canyon. It's a one-of-a-kind experience, the equivalent of driving into and through the crust of the Earth and into the mantle below. It is the path to the nether-world that has often been called the home of the devil.

Del Puerto Canyon lies just west of the Central Valley town of Patterson. A paved road, state route 130, connects Patterson with the Santa Clara Valley, but anyone thinking it would make a shortcut between the two localities is in for a rude awakening: curvy, narrow, with steep drop-offs, it is not a road for the faint-of-heart. It also has some extraordinary scenery and some absolutely fascinating geology. 

The lower canyon exposes 25,000 feet of late Mesozoic and early Paleogene marine sediments deposited in the forearc basin of the Cordilleran subduction zone that stretched the length of California. The middle stretches reveal the oceanic crust on which the sediments were deposited, the Coast Range ophiolite (the second-most complete section found in California). The uppermost canyon is the strangest environment of all, consisting of rocks that were once part of the Earth's mantle. The rocks are interesting, and so are the plants that survive on the ultramafic soils.

One of our students discovered an ammonite fossil on this trip!

The canyon also has a place in the history of California paleontology. The 25,000 feet of oceanic sediments provide an extensive record of fossil species, including the clams, snails, ammonites and shark teeth that are expected in such environments. Mesozoic marine reptiles have also been found in the region, including plesiosaurs, ichthyosaurs, and a new species of mosasaur, Plotosaurus bennisoni. The canyon was also the site of the discovery of California's first dinosaur, a species of duckbilled dinosaur called Saurolophus. It was discovered by 16-year-old Al Bennison of Gustine in 1936. We found a single fossil this trip, an ammonite. Someday, it'll be a dinosaur, right?

To me, the most interesting rocks are found in the upper canyon. The mantle of the Earth is a 1,800-mile-thick layer that starts at a depth of 15 or 20 miles beneath the continental crust. It is generally composed of a rock called peridotite or dunite, made up of the mineral olivine with varying amounts of pyroxene and various ores of chrome, mercury, magnesium, and copper. Peridotite is chemically unstable in surface conditions and alters mostly to serpentine. Many of the rocks we observed showed some degree of alteration. The rock below that looks like alligator skin (below) is composed of fractured chunks of pyroxene (the reddish-brown) and serpentine (the green fracture filling).

In a few spots one can find some relatively unaltered peridotite (below).

We also found some samples of chromite ore. Chrome contributes to the production of stainless steel and has applications in forming armor. During peacetime, there are cheaper sources of chrome overseas, but during wars the supplies may be cut off. During the world wars, chromite was mined in the upper canyon and transported by rail down the canyon to Patterson to be processed.

The little black grains are chromite

The upper canyon was also a source of cinnabar, a mercury sulfide mineral. Despite its toxic nature, mercury was a critical component in the processing of gold ores during the Gold Rush. Miners could often make a good wage mining the ores, but they would do so at great risk to their health. Luckily the temptation to gather mercury ore was not possible as the mine properties are fenced off.

The last part of our journey is the saddest. The lower canyon, the first five-and-a-half miles, is under threat. A local irrigation district is intent on building a reservoir that will flood much of the canyon under hundreds of feet of water. It will serve no purpose other than to store excess water from the California Water Project (in the rare years when such excess is available). It would then be used in subsequent drought years. In other words, it would be an evaporation pond, a waste of water. There would be no recreational facilities. Numerous archaeological sites would be flooded, and precious prairie and riparian ecosystems would be destroyed.

Del Puerto, ("the Gate") Credit: Elias Funez, Save Del Puerto Canyon

There are geological concerns. The dam itself would be constructed a quarter mile from a potentially active fault system (there was an earthquake swarm in the canyon earlier this year). There are seven gigantic earthflows and slumps, one a mile long, that would be partially inundated and potentially reactivated. And it's true I'm not an engineering geologist, but I question the stability of the shale, siltstone and sandstone that the dam abutments would be anchored in. I wasn't reassured by the environmental impact report.

In any case, there is community opposition to this misguided plan. It will do nothing to benefit the local community even while it threatens nearby cities. If you would like to learn more, and support efforts to stop this boondoggle project, please contact the organization Save Del Puerto Canyon. It would be such a shame to destroy yet another beautiful place in service to economic benefits for the very few.

 

Travels in Cascadia: Sitting Woman Falls. She's Sitting on Geological Pillows.

There are so many charming little corners to be found on Vancouver Island. We were well underway on our two-week field course on the geology and anthropology of British Columbia, and on this day we had already explored the Sooke Potholes and the base of the ocean crust at East Sooke Park (along with a couple of interesting petroglyphs). It was getting late in the afternoon and the crew was getting pretty tired, but I had heard that there was another site of interest at the end of a short trail, so we made one more stop. It was a place called Witty's Lagoon, which sounds like a theme park or something, but it actually is a geologically interesting section of coastline along the Salish Sea.

This area (and indeed all of Vancouver Island) was covered by glacial ice as recently as 13,000 years ago. When the ice melted, sea level rose to cover some of the previously exposed lands forming a series of bays and coves. Witty's Lagoon is a nice example of one of these, and it is largely unaffected by urban development. Metchosin Creek flows over a ledge of basalt to form Sitting Woman Falls at the upper end of the cove (above).

The basalt, part of what is called the Crescent Terrane, has an interesting story to tell. The basalt erupted on the floor of the Pacific Ocean around 50 million years ago at a divergent plate boundary. It originally melted because of the release of pressure at the mid-ocean ridge, and accumulated in plutons several miles beneath the ocean floor. As the crust spread apart, fractures formed and the basalt followed the breaks all the way up to the sea floor where it erupted out. When basalt erupts in water, it forms odd looking lumps about the size of old-fashioned down pillows, around two or three feet across. These pillows accumulated in layers hundreds of feet deep.

The sequence of gabbro plutons, sheet dikes (the filled fractures), and pillow basalts constitute an ophiolite sequence that in this area is called the Metchosin Igneous Complex. In our previous post we had a chance to see the gabbro as it was exposed on the shoreline of East Sooke and Becher Bay. We didn't get to see any good examples of the dikes, but the cliff at Sitting Woman Falls was composed of pillow basalts. I've zeroed in on the section of the cliff to the right of the falls in the picture above. The pillows are not really well exposed, so I've cheated by adding some pictures below of pillow basalts that we've seen elsewhere in Washington and California.

The picture above shows pillows exposed in the cliffs at Cape Disappointment at the mouth of the Columbia River in Washington. Below we can see some pillow basalts exposed near Nicasio on the Marin Headlands in California.

It's incredible to think of the forces involved in taking the oceanic crust from the bottom of the sea, and mashing it into the edge of the North American continent where it ended up being exposed at Witty's Lagoon, and indeed throughout the region, including the high peaks of the Olympic Peninsula across the Strait of Juan de Fuca.

Travels in Cascadia: Walking Under the Ocean Floor at East Sooke Bay, British Columbia

We continued our explorations of British Columbia with a hike at the south end of Vancouver Island at East Sooke. It's an unusual place, out of place with the rocks that make up most of the island. The majority of Vancouver Island is made up of metamorphic rocks of the Wrangellia Terrane. These rocks originated as island arcs and continental fragments in the Pacific Ocean which added to the west coast of North America as the ocean crust sank beneath the continent at the Cascadia Subduction Zone.

Source: Chris Yorath

But the south tip of the island is made up of rocks related to the Olympic Peninsula which lies 20 miles away across the Strait of Juan de Fuca. These rocks are parts of the ocean crust, and are called the Metchosin Igneous Complex, or the Metchosin Ophiolite. They formed in Eocene time, around 50 million years ago as vast amounts of basaltic lavas spilled out on the Pacific Ocean floor

The Olympic Mountains seen from East Sooke across the Strait of Juan de Fuca

Ophiolites are generally considered to be slices of oceanic crust that form at divergent plate boundaries. The oceanic crust is pulled apart by extensional forces, relieving pressure on the underlying asthenosphere where the rocks are close to the melting point. The loss of pressure causes some melting to take place, and the resulting basaltic magma rises through fractures caused when the sea floor is pulled apart. An ophiolite has three distinct parts, with pillow basalts making up the ocean floor (more on pillows in a coming post), sheet dikes (the fractures), and gabbro plutons at the base. Gabbro is a coarse-grained igneous rock with the same composition as basalt (it cools slowly, allowing for crystal growth). A pluton is any kind of rock that has been intruded into the crust.

East Sooke Regional Park lies a few miles west of Victoria along the shoreline of the Salish Sea. For a coastal park it has an unusual 'feel'. Because the Salish Sea consists of a series of straits and inlets, wave energy is considerably diminished, at least at the times that I've been able to visit. The waves barely register and the shoreline seems more like a large lake, much like Lake Tahoe in my own home region. But the water is definitely salty!

My goal for our class this day was to get a close look at the rocks of the gabbro pluton portion of the ophiolite. In other words, we were going to go walking beneath the ocean floor. The class, a combined dyad of geology and anthropology students had other ideas. The anthropologists slightly outnumbered the geologists, so they were intent on finding some reported petroglyphs in the region. We went hiking on the Alyard Farm Trail, which was a loop of about two miles, first along the rocky shore, and ending in a thick conifer forest.

Luckily, the petroglyphs had been carved out of boulders of the gabbro, so we got the best of both worlds, with some glacial grooves as icing on the cake. Can you see the first one in the picture below? Without looking ahead, can you tell what it was meant to be (remember the landscape setting)?

I'm told that this is the representation of a sea lion. One source on the internet (the arbiter of all truth) mentions the following myth about the petroglyph: "Long years ago a great supernatural animal like a sea lion killed many of the Becher Bay Indians while they were canoeing. The tribe nearly became extinct; the remaining members were afraid to go on the water until one day a mythical man caught the sea lion and turned him into the stone representation on Alldridge Point" (Anonymous, Report of BCPM, 1928).

Note the grainy nature of the rock in the picture below. Gabbro is a dark-colored plutonic rock that has the same composition as basalt, but the individual grains are visible because of the slow rate that the magma cooled. The gray minerals are plagioclase feldspar, while the black minerals are mostly a variety of pyroxene, perhaps augite. Small grains of olivine are scattered throughout the rock.

There is a second petroglyph nearby of a salmon (below), but it has seriously faded. Both petroglyphs are attributed to the T'Sou-ke First Nation people, but the age of the rock carvings is not known. They quite likely are thousands of years old, based on the amount of weathering.

I'll probably say something similar to this many more times as we continue our exploration of British Columbia, but here we go: if you ever have the opportunity to visit Victoria and Vancouver Island, set aside some time to explore the East Sooke area. In addition to the beautiful coastal trail, there is also the East Sooke Potholes, a series of deep pools eroded out of the rocks after the last ice age. We didn't have the time to explore further up the coast, but the guides mention a number of fascinating places to investigate.

I had three main resources for the geology in and around the city of Victoria and East Sooke:
The Geology of Southern Vancouver Island by Chris Yorath
Roadside Geology of Southern British Columbia by Bill Mathews and Jim Monger
Geology of British Columbia, A Journey Through Time by Sydney Cannings, JoAnne Nelson, and Richard Cannings.

A Look Back at Ten Years of Geotripping: Driving Through the Most Dangerous Plate Boundary in the World

Driving through the most dangerous (kind of) plate boundary in the world is actually not very easy to do. Subduction zones, with the exception of the volcanoes, are mostly deep under the sea. But Central California is a unique case, being an ancient subduction zone that has been uplifted and exposed by erosion, so that interested parties can literally drive through what once was miles underground or at the bottom of the deepest oceans. I got the idea for this blog series when I spent an afternoon driving the winding road that travels over the Coast Ranges at Lick Observatory, and down through Del Puerto Canyon into the Great Valley. It's the equivalent of driving twenty or thirty miles into the Earth's crust. Looking back over the titles, I'm worried that I am using up my lifetime supply of bad jokes...

I've been reviewing the archives this week to find some of my favorite posts from ten years of geoblogging. This compilation appeared on July 4, 2015.

Without a doubt, subduction zones are the most dangerous plate boundaries on the planet. Divergent plate boundaries produce earthquakes and occasional volcanoes, but nothing on the fearsome scale of the calderas and stratovolcanoes and magnitude 9 earthquakes experienced at convergent boundaries. Transform boundaries produce earthquakes, but they are magnitudes smaller than those produced at convergent boundaries (despite what certain Hollywood movies have asserted recently). Hot spots, while not a plate boundary, can produce huge caldera complexes like Yellowstone, but such monsters have not had much of an effect on human history of the last few thousand years. It is the subduction zones of our planet that have caused the most human misery, in the form of massive earthquakes, tsunamis, and violent volcanic eruptions.

We have been driving through an example of one of the most dangerous plate boundaries in the world, but our particular example has been inactive for a very long time. Central California was a subduction zone complex for more than 150 million years, primarily during the Mesozoic era, but it changed into a transform boundary only a few tens of millions of years ago. The San Andreas fault is the resulting feature, and it is capable producing damaging earthquakes, but even the most destructive quakes, like 1906 in San Francisco (death toll 3,000), is but 1/30 of the energy of a magnitude 9 quake like that of Indonesia in 2004 (where the resulting tsunami killed 200,000 people).

It's taken a couple of months to work through our journey, so I've compiled all of the posts here so one can catch the continuity of the story. Here goes...

A New Blog Series

The introduction to the new series, a geological transect from the California Coast to Yosemite Valley, crossing an ancestral subduction zone that once caused geological havoc in a zone from Mexico to Canada (and still is in a few places).

Reconnaissance

An overview (in the most literal sense) of the lands we will traverse on our journey. We have a look at central California from above.

These Rocks are All Wrong!

Granite is exposed in the rocks of the Point Reyes Peninsula. But the arrangement of rock and sediment in subduction zones suggests that granite shouldn't be anywhere near here. It's the San Andreas fault. In California, it's always the San Andreas' fault.

Looking for the Big One

The peace and serenity of Tomales Bay belies a violent past. The San Andreas fault slices right through the bay, and produces large earthquakes with disturbing irregularity. The epicenter of the San Francisco quake in 1906 was not far from here.

Welcome to Geology's Junk Drawer

The Marin Headlands began as a giant collector of geological flotsam and jetsam from the crust of the Pacific Ocean. The jumble of rocks accumulated in an accretionary wedge, and were later lifted up into the mountains of the Marin Peninsula.

Geology's Junk Drawer on the Marin Headlands

Exploring the hidden corners of the Marin Headlands, we find Redwood forests, beautiful views of San Francisco, and disturbing reminders of World War II.

Terra Fatale on the Marin Headlands

Although the subduction zone that formed the rocks of the Marin has been extinct for a long time, there are still plenty of hazards remaining in the region, both geological and nautical. The Point Bonita Lighthouse has been present in one form or another for 160 years. It hasn't always worked, as there are upwards of 300 shipwrecks in the area. There are other hazards too.

The Alien Bursts Forth in the Diablo Range!

We head across San Francisco Bay and start an arduous journey through the Diablo Range. The range formed as an exotic (read "alien") terrane pushed upwards through the sediments of the Great Valley Group, piercing the surface and rising into the sky. John Hurt would no doubt approve...

Exploring the Belly of the Beast in the Diablo Range

We make the first part of a long drive through a rugged portion of the Diablo Range, one of the largest sub-ranges in the Coast Ranges of California. Along the way we cross through two exotic terranes of rocks that had been carried miles deep into the crust in the accretionary wedge of the subduction zone.

At the Portal of Hell in Diablo Range

Making our way down Del Puerto Canyon in the Diablo Range, we do the equivalent of traveling through the crust of the Earth all the way into the mantle, finding outcrops of peridotite and dunite, rocks containing the mineral olivine among others. For the mercury miners, this truly was a portal to Hell.

Exploring the Ocean Crust without Unobtanium

Del Puerto Canyon cuts a swath through the Coast Range Ophiolite, the remnants of the ocean crust that once lay at the bottom of the Pacific Ocean. Though mostly in private ownership, the canyon is one of the most scenic in the Coast Ranges, and a pair of county parks in the upper reaches invite exploration.

Into the Realm of the Drowning Dinosaurs

Sediments accumulated in a deep trough along the west coast of North America called a forearc basin for upwards of 100 million years. The layers reached a depth of 5 miles! In those waters swam mosasaurs (yes, like in the recent Jurassic World movie, but they forty feet long, not a hundred), plesiosaurs, ammonites, and occasionally a drowning dinosaur. The first discovery of a dinosaur in California happened here in 1936.

The Sea Floor that became the Greatest Agricultural Region on Earth

The American Serengeti is a vast plain 400 miles long and 50 miles or so wide that once was the sea floor. The grasslands of the Great Valley once supported millions of migratory birds and grazing animals. It still supports millions of organisms, but these days, those organisms are humans. 95% of the original prairie has been developed for agriculture and the region produces a quarter of the nation's produce. And all of the almonds and walnuts.

In the Pleistocene, a Different Kind of Danger

The Great Valley would have been a most dangerous region for a different reason in the Pleistocene. Among the great herds of grazing animals there were predators, and they were adapted to bringing down giant prey, not the small game we find today. Gigantic Short-faced Bears, Saber-tooth cats, American Lions, Jaguars, and Dire Wolves.

The Dr. Who of Mountain Ranges

At least three Sierra Nevada ranges have existed throughout time. They might have even once been higher than today. The distorted deformed metamorphic rocks tell the story of the earlier ranges.

A Gentle Landscape Belies a Fiery Past

The Valley Springs formation, exposed throughout much of the Sierra Nevada foothills region, forms gentle grass and oak covered slopes, but the rock is made of volcanic ash that originated in monumental explosions millions of years ago. The ash came from gigantic calderas, some of which were hundreds of miles away in central Nevada.

A Landscape Buried in Hot Mud, and a 6-foot Long Saber-tooth Salmon

A lot of volcanoes in the world are made of mud. Lots and lots of mud. But this mud formed in violence. The Mehrten formation of the Sierra Nevada has other surprises too: gigantic tortoises, and six-foot long salmon...with fangs...

A Tale of Two Subduction Zones

There have actually been at least two subduction zones in California. Remains of the older one still make up the rocks of the Sierra Nevada Mother Lode, and those rocks were the source of gold in the Gold Rush.

Exploring the Underside of the Volcano

We wrap up the series in the heart of the ancient magmatic arc: Yosemite Valley. Walking among the towering cliffs, we are reminded that the rocks were actually formed within the magma chambers of volcanic systems, perhaps similar to Lassen Peak, Mt. Shasta, or even at times, Yellowstone.

Driving Through the Most Dangerous Plate Boundary in the World: A Compilation of Fear(somely cool geology)

Without a doubt, subduction zones are the most dangerous plate boundaries on the planet. Divergent plate boundaries produce earthquakes and occasional volcanoes, but nothing on the fearsome scale of the calderas and stratovolcanoes and magnitude 9 earthquakes experienced at convergent boundaries. Transform boundaries produce earthquakes, but they are magnitudes smaller than those produced at convergent boundaries (despite what certain Hollywood movies have asserted recently). Hot spots, while not a plate boundary, can produce huge caldera complexes like Yellowstone, but such monsters have not had much of an effect on human history of the last few thousand years. It is the subduction zones of our planet that have caused the most human misery, in the form of massive earthquakes, tsunamis, and violent volcanic eruptions.

We have been driving through an example of one of the most dangerous plate boundaries in the world, but our particular example has been inactive for a very long time. Central California was a subduction zone complex for more than 150 million years, primarily during the Mesozoic era, but it changed into a transform boundary only a few tens of millions of years ago. The San Andreas fault is the resulting feature, and it is capable producing damaging earthquakes, but even the most destructive quakes, like 1906 in San Francisco (death toll 3,000), is but 1/30 of the energy of a magnitude 9 quake like that of Indonesia in 2004 (where the resulting tsunami killed 200,000 people).

It's taken a couple of months to work through our journey, so I've compiled all of the posts here so one can catch the continuity of the story. Here goes...

A New Blog Series

The introduction to the new series, a geological transect from the California Coast to Yosemite Valley, crossing an ancestral subduction zone that once caused geological havoc in a zone from Mexico to Canada (and still is in a few places).

Reconnaissance

An overview (in the most literal sense) of the lands we will traverse on our journey. We have a look at central California from above.

These Rocks are All Wrong!

Granite is exposed in the rocks of the Point Reyes Peninsula. But the arrangement of rock and sediment in subduction zones suggests that granite shouldn't be anywhere near here. It's the San Andreas fault. In California, it's always the San Andreas' fault.

Looking for the Big One

The peace and serenity of Tomales Bay belies a violent past. The San Andreas fault slices right through the bay, and produces large earthquakes with disturbing irregularity. The epicenter of the San Francisco quake in 1906 was not far from here.

Welcome to Geology's Junk Drawer

The Marin Headlands began as a giant collector of geological flotsam and jetsam from the crust of the Pacific Ocean. The jumble of rocks accumulated in an accretionary wedge, and were later lifted up into the mountains of the Marin Peninsula.

Geology's Junk Drawer on the Marin Headlands

Exploring the hidden corners of the Marin Headlands, we find Redwood forests, beautiful views of San Francisco, and disturbing reminders of World War II.

Terra Fatale on the Marin Headlands

Although the subduction zone that formed the rocks of the Marin has been extinct for a long time, there are still plenty of hazards remaining in the region, both geological and nautical. The Point Bonita Lighthouse has been present in one form or another for 160 years. It hasn't always worked, as there are upwards of 300 shipwrecks in the area. There are other hazards too.

The Alien Bursts Forth in the Diablo Range!

We head across San Francisco Bay and start an arduous journey through the Diablo Range. The range formed as an exotic (read "alien") terrane pushed upwards through the sediments of the Great Valley Group, piercing the surface and rising into the sky. John Hurt would no doubt approve...

Exploring the Belly of the Beast in the Diablo Range

We make the first part of a long drive through a rugged portion of the Diablo Range, one of the largest sub-ranges in the Coast Ranges of California. Along the way we cross through two exotic terranes of rocks that had been carried miles deep into the crust in the accretionary wedge of the subduction zone.

At the Portal of Hell in Diablo Range

Making our way down Del Puerto Canyon in the Diablo Range, we do the equivalent of traveling through the crust of the Earth all the way into the mantle, finding outcrops of peridotite and dunite, rocks containing the mineral olivine among others. For the mercury miners, this truly was a portal to Hell.

Exploring the Ocean Crust without Unobtanium

Del Puerto Canyon cuts a swath through the Coast Range Ophiolite, the remnants of the ocean crust that once lay at the bottom of the Pacific Ocean. Though mostly in private ownership, the canyon is one of the most scenic in the Coast Ranges, and a pair of county parks in the upper reaches invite exploration.

Into the Realm of the Drowning Dinosaurs

Sediments accumulated in a deep trough along the west coast of North America called a forearc basin for upwards of 100 million years. The layers reached a depth of 5 miles! In those waters swam mosasaurs (yes, like in the recent Jurassic World movie, but they forty feet long, not a hundred), plesiosaurs, ammonites, and occasionally a drowning dinosaur. The first discovery of a dinosaur in California happened here in 1936.

The Sea Floor that became the Greatest Agricultural Region on Earth

The American Serengeti is a vast plain 400 miles long and 50 miles or so wide that once was the sea floor. The grasslands of the Great Valley once supported millions of migratory birds and grazing animals. It still supports millions of organisms, but these days, those organisms are humans. 95% of the original prairie has been developed for agriculture and the region produces a quarter of the nation's produce. And all of the almonds and walnuts.

In the Pleistocene, a Different Kind of Danger

The Great Valley would have been a most dangerous region for a different reason in the Pleistocene. Among the great herds of grazing animals there were predators, and they were adapted to bringing down giant prey, not the small game we find today. Gigantic Short-faced Bears, Saber-tooth cats, American Lions, Jaguars, and Dire Wolves.

The Dr. Who of Mountain Ranges

At least three Sierra Nevada ranges have existed throughout time. They might have even once been higher than today. The distorted deformed metamorphic rocks tell the story of the earlier ranges.

A Gentle Landscape Belies a Fiery Past

The Valley Springs formation, exposed throughout much of the Sierra Nevada foothills region, forms gentle grass and oak covered slopes, but the rock is made of volcanic ash that originated in monumental explosions millions of years ago. The ash came from gigantic calderas, some of which were hundreds of miles away in central Nevada.

A Landscape Buried in Hot Mud, and a 6-foot Long Saber-tooth Salmon

A lot of volcanoes in the world are made of mud. Lots and lots of mud. But this mud formed in violence. The Mehrten formation of the Sierra Nevada has other surprises too: gigantic tortoises, and six-foot long salmon...with fangs...

A Tale of Two Subduction Zones

There have actually been at least two subduction zones in California. Remains of the older one still make up the rocks of the Sierra Nevada Mother Lode, and those rocks were the source of gold in the Gold Rush.

Exploring the Underside of the Volcano

We wrap up the series in the heart of the ancient magmatic arc: Yosemite Valley. Walking among the towering cliffs, we are reminded that the rocks were actually formed within the magma chambers of volcanic systems, perhaps similar to Lassen Peak, Mt. Shasta, or even at times, Yellowstone.