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.

 

The Hawai'i That Was: The Beginning of All Things, (Ba)salt of the Earth

There are lots of places that are associated with a particular kind of rock. There's the granite of the Sierra Nevada, or the sandstone of Zion National Park. Geologists think Franciscan graywacke sandstone when someone mentions the California Coast Ranges. But nearly every mainland location is really made of a variety of different rocks. That's not the case with the Hawaiian Islands. There is but one rock. It comes in many guises, but it is compositionally the same thing: basalt.

A pahoehoe flow from Kilauea from 2004. The flow was only a few days old and looks silver because of a thin layer of volcanic glass that degrades and falls away within weeks or months.

That's the starting point of our journey through The Hawai'i That Was. Hawai'i began as basalt, and until the eroded rocks are covered by coral reefs, that's all there will be, the basalt or the weathered components of the basalt. Every island in the chain began as a series of sterile tracts of the black volcanic rock.

That's not to say that basalt in Hawai'i is everywhere the same. It originates in the same place, as a "partial melt" magma deep in the Earth's mantle at a (probable) hot spot. Magma results from the melting of rocks, but rocks are made of different kinds of crystals, and different crystals melt at different temperatures. So a partially melted magma will be made of the minerals that melt at slightly lower temperatures. In the case of Hawai'i, the original rock, peridotite (or related rock like dunite), is composed primarily of olivine and a few other minerals, but the partial melt produces a rock composed of pyroxene, calcium-rich plagioclase and lesser amounts of olivine. Two kinds of lava, not easily distinguished in the field, are found in Hawaii: a sodium-depleted tholeiitic basalt (early-stage eruptions), and a sodium-rich alkali basalt (late-stage eruptions). At times, the magma will bring bits of peridotite to the surface as clots in the lava like the one in the picture below. These clots are called xenoliths ("alien rocks").

A mantle xenolith in basalt. The green mineral is olivine (it weathers to red iron oxide quickly in the moist climate of Hawai'i)

Olivine is a semi-precious gemstone, and is occasionally visible as phenocrysts in the basalt. Given the name, it's not hard to guess that the stone is green in color. Hawai'i hosts one of the few green sand beaches to be found anywhere on the planet (which we visited; the story will come in a follow-up blog).

Olivine phenocrysts in vesicular (holey) basalt at Pu'ohonua o Honaunau National Historical Park

Eruptions of basalt can vary in temperature, gas content, water content and other factors. Depending on the circumstances of the eruption, basalt can take the form of a pahoehoe flow (see the second picture above) where the surface is smooth or ropy looking. It can also take a rough and blocky aspect like the one in the picture below called an a'a flow (believe it or not students misspell this word sometimes). Lava flowing into the sea can explode into sand-sized particles (forming black-sand beaches), or pillow-shaped lobes called (not surprisingly) pillow lavas.

Explosive eruptions of basalt are fairly rare on Hawai'i, but they do happen. The rapidly cooling lava may not even form crystals, forming a glass instead. The glass can take the form of a gold-colored basaltic pumice (below), a spongy material with the consistency of styrofoam.

Basaltic pumice at the Lyman Museum in Hilo

One of the oddest materials to result from a basaltic eruption happens when molten lava flies through the air trailing long thin strands of glass called Pele's Hair. The strands are so delicate it's amazing they can be found at all, much less in bunches like the sample below from the Lyman Museum in Hilo. I've only found single strands out in the wilds.

Pele's Hair at the Lyman Museum in Hilo

Larger chunks of molten lava can twist during flight into so-called lava bombs. In the picture below, the sample is lying in a bed of cinders, the smaller bits of explosive eruptions. Take some serious advice here: if you collect lava bombs in Hawai'i and you are going through airport security, and they ask what you have in your luggage, DO NOT use the word "bomb". The results are not happy or convenient, based on a true story (thankfully not mine; I have plenty of lava bombs from California).

Basalt is the beginning of all that is in the Hawaiian Islands. The islands began as thousands upon thousands of lava flows, the soils on which plants and animals survive are derived from the weathering of basalt, and the platform on which coral reefs later grow at the end of the island's existence is basalt. Basalt forms the base on which all travels took place and basalt was the building stone of choice (the only choice).

The Mamalahoa Trail, that stretches from Kona to Puako. It was built in the 1800s.

The islands started as sterile basalt, but as the saying goes, "life finds a way". Certain native ferns and trees are able to colonize the rock even in the absence of anything resembling soil. In the picture below, native 'Ohi'a trees are growing in basalt that erupted in 1959. Barring any more eruptions (a risky proposition in this particular spot on Kilauea), this will be a rainforest in a few centuries.

Native 'Ohi'a trees growing in a recent basalt flow in the interior of the Kilauea Iki crater, which erupted in 1959.

It was June 1st. Although Mrs. Geotripper and I had been on the islands for nearly a week doing some reconnaissance, the students were now arriving at the airport, and we were gathering our class together. Our exploration of the Hawai'i That Was had reached the starting gate.

A Netherworld Incompatible with the Existence of Life: The Mantle Exposed at Del Puerto

Our journey into the interior of the Earth has reached a remarkable boundary, the base of the oceanic crust. Beyond the crust, underneath the Mohorovičić discontinuity, lies the mantle, a layer that extends halfway to the center of the Earth. We have been driving up Del Puerto Canyon, a scenic route that crosses the Diablo Range in the central part of California's Coast Ranges. The rocks at the headwaters of the canyon have formed a landscape unlike any other. It's a landscape of the underworld, the netherworld.

Serpentine in the upper canyon. Serpentine is highly altered mantle material.

The netherworld is a place in the mythology and religion many cultures, a dark and hot place deep within the Earth that is the habitation of death. It's no place that a human would ever want to be. And yet, here we were, on a sunny December afternoon. It's not necessarily a place of death, but at the same time the rocks were never really able to support life. They formed in an environment where life was impossible, and life at the surface is ill-adapted to survive in such rocks.

The Earth's mantle is composed of a variety of ultramafic rocks, rocks rich in iron and magnesium and a suite of elements not commonly found in the overlying crust: mercury, chromite, nickel, platinum and cobalt. The rocks found in the upper canyon include varieties of dunite and peridotite, which are olivine-rich rocks. In most places such rocks are quickly altered into serpentine, California's state rock, but in upper Del Puerto Canyon, you can find largely unaltered ultramafic rock.

The plant cover is strange, and quite unlike any found on "normal" crustal rocks. Grass is almost nonexistent, and the ubiquitous California oak trees are nowhere to be found. There are too many toxic substances in the soil, and not enough of needed nutrients. The few scattered plants that can survive on such soils include the California endemic Gray Pine and some species of manzanita. A great many wildflowers have adapted to these soils, and the slopes can be quite colorful in wet years.

The rocks have yielded economical amounts of mercury, chromite and mercury. Our stop at the head of the canyon was at an old chromite mine. Despite the obvious use to make cars sparkle and shine, chrome has more important uses in making stainless steel and armor. During peaceful times, chrome is cheaper from overseas sources, but in wartime, the ores in the canyon become valuable. They were last mined during World War II.

Mercury was sought for use during the Gold Rush as a way to separate gold from the ore. There are extensive deposits in the upper canyon and just beyond the pass at the head of the canyon. Mercury mining was lucrative, but deadly. Miners who absorbed mercury into their nervous system quickly developed symptoms and often died. Mercury continues to poison water and sediments in the Central Valley and San Francisco Bay.

Altered ultramafic rocks from the upper canyon

The upper canyon has numerous kinds of rocks to observe. The two pictures above show ultramafic rocks that were in the process of altering to serpentine. The core sections are composed of enstatite pyroxene (which I believe is also known as bronzite when slightly altered like this).

Chromite ore from the upper part of Del Puerto Canyon

It's not too difficult to find small metallic grains of chromite. It takes a bit more searching to find some relatively unaltered peridotite or dunite. It's a beautiful rock, with the rich green of the olivine, which is also known as the gemstone peridot. That's right, there are outcrops of gemstones in the upper canyon! If you are ever up that way, take a close look at the rocks near mile marker 18.

Peridotite from the upper reaches of Del Puerto Canyon

So, our journey into the interior of the Earth is pretty much done. The rocks of the core are just too deep to visit, even with unobtainium (movie reference! The Core, and Avatar). It's a pleasant way to spend an afternoon, exploring the netherworld in the bright light of day!

If you want to pay a visit to Del Puerto Canyon, it can best be accessed from the town of Patterson in the Central Valley southwest of Modesto. A road (Mines Road) reaches the area from Livermore, and a slow winding road travels over Mt. Hamilton and Lick Observatory from San Jose in the Bay Area. There is a campground and day use area in the upper canyon (Frank Raines Park and Minniear Day Use), but most of the rest of the canyon is private land. Stay on the road!

Driving Through the Most Dangerous Plate Boundary in the World: At the Portal of Hell in the Diablo Range

At the portal of hell? For the miners who once worked these tunnels, it was...

I miss the tabloids sometimes. Sure, there's the Onion, which gets mistaken for real news sometimes. But there was nothing like standing in the grocery store lines perusing headline after headline of "real" news, like Elvis sightings, UFO reports, and "Loch Ness Monster Meets Yeti" stories. On extended field trips when group morale was slipping a bit, I could pick up a copy of one of those tabloids and read stories around the campfire, and it worked like magic to bring a group out of the doldrums.

Source: http://www.snopes.com/religion/wellhell.asp

One story has stuck in my mind over the years, the one about the Russians (or Alaskans, or Norwegians) who were digging the world's deepest well on the Kola Peninsula in Russia (or on the North Slope, or in Scandinavia) and when they reached a depth of 7 miles (or 9 or 12), the drill started spinning wildly, and they measured temperatures of 2,000 degrees, but scariest of all, they lowered a microphone (into the 2,000 degrees...) and heard the unmistakeable sounds of screaming souls in Hell. In some versions, gases rose and took the form of the devil, and...well, you get the general picture. As can be seen from the link at the start of the paragraph, the story spread so widely that it merited a Snopes article. What does it tell you that some people (including one or two of my students) took this seriously?

In any case, we are back on our journey through the most dangerous plate boundary in the world, and when we finished our last episode we had passed through the Franciscan Complex, the rock unit that formed in the accretionary wedge of California's Mesozoic subduction zone. We are now making our way down the eastern margin of the Diablo Range through the gorge of Del Puerto Canyon. The association of "Diablo", and "Puerto" ("Devil" and "Portal") is what brought to mind the "screams of the damned" in the old tabloids.

The geologists were trying to dig a hole into the deep crust. They wanted perhaps to break through the continental crust and into the underlying mantle, a layer of peridotite and other ultramafic rocks that make up about 80% or so of the Earth's volume. They failed, but what an effort they made! The thing is, if one really wants to reach the mantle, there is an easier way: find the places where the mantle has risen to the Earth's surface. And that's what happened in Del Puerto Canyon.

Peridotite is composed largely of the mineral olivine (the gemstone peridot). The Earth's mantle is made of gemstones!

As we travel down this canyon we are going to do the literal equivalent of traveling from the Earth's mantle upwards through four or five miles of the oceanic crust, and then "climb" through 25,000 feet of oceanic sediments. All while coasting down a pleasant country avenue in one of the most scenic of the Coast Range's canyons. Along this journey we will also finally leave behind the accretionary wedge of the Franciscan subduction zone, and enter into the intriging forearc basin.

The ultramafic rocks of the upper canyon host a number of unusual minerals and ores. Among them are mercury and chromite. The mercury mined here was used in the process of separating gold from the tailings in the Mother Lode on the other side of the Great Valley. As I understand it, one could make very good wages mining the mercury, but you didn't last long at the job. The mines literally killed the miners. For them, the tunnels really were the portals of Hell. The mercury vapor in the air got into their nervous system, first destroying their minds, and then their bodies.

Chromite from upper Del Puerto Canyon

The chromite that was mined in the upper canyon was not nearly so dangerous. Chromite is of course the source of chrome, which most people associate with shiny car accessories. The most important use of the metal is much more pervasive: it is a major component of stainless steel. The United States usually imports cheap ores from overseas, but during periods of war domestic sources were exploited, and that's what happened in the upper part of Del Puerto Canyon. The road we are traveling was once a railway that serviced the mines.

The orange streaks in the ultramafic rocks of Del Puerto Canyon are slickensides, scratch marks left by faulting

There is a large quarry face in the upper canyon where the rocks can be readily observed. The unweathered rock is dark in color, but weathers readily into an iron oxide rich patina. The region came to be known as the Red Mountain Mining District. The ultramafic rocks are very poor in important in plant macronutrients, and also contain some toxic elements as well. The vegetation on the slopes reflects the difficulty of surviving in this poisonous chemical environment. A number of the species found here are endemic to California and the Coast Ranges. And few invasive species ever gain a roothold on these slopes.

Next, we'll see if we can find the oceanic crust, the rock sequence known as the Coast Range Ophiolite. Stay tuned...

Some Spring Wildflowers from the Coast Ranges, and a mini-quiz

Lindley was apparently a busy botanist. Being the non-botanist I am, I was trying to identify some of the spring wildflowers I photographed last week in Del Puerto Canyon in California's Diablo Range. I tracked down two of them, and both were named for Lindley. I don't know if it was for the same person, but I do see on the Google that there was a John Lindley who was an English botanist in the 1800s.

But first there are the thistles we saw. I know that some of the thistles are invasive weeds, and in fact the star thistle is devastating pastures all over the state. And killing horses in the process. I don't know if the other thistles are natural or invaders. Hopefully my botanist readers can clue us in.

 Still, the thistles are a bright addition to the landscape.

Then there is the first Lindley, the Lindley's Blazing Star (Mentzelia lindleyi). From a distance, I tend to mistake them for poppies, but there is no mistaking the difference up close. This is one of the wildflowers that is tolerant of serpentine soils.

 The other Lindley is not actually a flower, but a seed pod. It is the dandelion-like Silver Puff (Uropappus lindleyi).  The actual flower is much like a dandelion too.

The next flower is not a Lindley, but it is very strange looking. It is apparently called the Chia (Salvia columbariae). The seeds of this flower were an important component of the diet of a number of Native American groups in California and the southwest, and also had medicinal uses. It also appears to be a serpentine-tolerant species.

Then there are the two that I couldn't identify after a brief search. There is the purple flower below...

 ...and what appears to me to be some kind of Monkey Flower, but as in all things botanical, I am open to correction!

I took three different trips to three very different localities in the last couple of weeks. The first was a spur of the moment exploration of the eastern Great Valley and lower Sierra Nevada foothills near New Hogan Reservoir and Valley Springs, followed by a pair of laboratory field trips to Del Puerto Canyon in the Coast Ranges where I took these wildflower pictures. Then, on Saturday, it was another field trip to Yosemite Valley, where we saw Half El Capitan, Half Cathedral Rocks, Half Yosemite Falls, and No Dome. Check out the different kinds of scenery and rocks...

The Great Valley with Mount Diablo in the distance

The lower reaches of Del Puerto Canyon, showing thick layers of the Great Valley Group,
and a pretty incredible landslide (slump and earthflow)

Some tightly folded radiolarian cherts in the middle stretches of Del Puerto Canyon

Olivine peridotite from the upper end of Del Puerto Canyon

An overcast day in one of the best places in the world to see granitic rock exposed in all its splendor

It's hard to imagine any geological region more different than these three places. The utterly flat and mostly featureless Great Valley, the soaring granite cliffs of Yosemite Valley and the High Sierra Nevada, and the (usually) muted slopes of the Coast Ranges, in this instance the Diablo Range. And yet there is a single geologic entity that joins all of them together.

This isn't exactly a mystery to be solved by the readers, more a lead-in to the next post, but you are welcome to comment if you can answer what exactly it is that links these disparate features of California's landscape.