Wednesday, April 15, 2015

A Fleeting Spring in a Horrible Drought: A Day in Yosemite Valley

There are so many moments when I want to deny the reality of the California drought. It has been relentless, the winter air warm and dry, the soil crunching under my feet at a time when it should be muddy and covered with vegetation. Even though my backyard rain gauge says we've had a normal year for precipitation, the reality is that it almost all fell in December, and almost none fell as snow in the Sierra Nevada. The snowpack is 5% of normal. Five percent! It's still April, and the main pulse of snowmelt in the mountains has already taken place when it should be happening in May and June. The spring season is fleeting this year, and that's the background to my trip to Yosemite Valley last weekend.
It was incredibly beautiful up there as it always is, but there were signs of a stressed environment. The forest is showing large patches of dead and dying trees. Dry spring conditions mean the trees have less sap to fight off pine-borer beetles which are then able to kill the trees. The valley does in fact have too many trees, but I'd rather not see them die off this way.
Bridalveil Fall and the Leaning Tower
There is still water in the waterfalls, but of course they should be booming and flooding, not merely falling. Visitors in the height of summer this year need to scale back some of their expectations. Yosemite without waterfalls is still an incredible place, but they shouldn't be dry by May. 
I was able to get a unique view of the Cathedral Rocks from the middle of the Merced River. At this time of year I should have been drowning in the flood, not standing on a rock. 
A very pretty sight for this time of year is the blooming of the Dogwood trees in the valley. The white "petals" aren't actually flowers, they are modified leaves. The actual flowers are at the center. I have to admit it's been awhile since I've seen such a colorful explosion of the flowers.
The Redbuds were mostly past their main blooming period, but there were still a few of them around.
The rocks are more or less eternal, though, at least from human standards. They could care less whether there is a drought or not. Some rocks will come tumbling down here and there, but in a thousand years, the valley walls will look pretty much the same. Below is North Dome from Curry Village.
The meadows are green, but are already showing a bit of brown in places. It's really been dry. Below is Stoneman Meadow, with Royal Arches, North Dome, and Washington Column behind.
The bridges of Yosemite Valley are beautiful human works of art. The placid Merced River flows under Stoneman Bridge with the bright green of newly awakened Cottonwood trees in the background. As pretty as it is, the river should be surging and flooding right now, not flowing gently. 
And that's why I want to deny the reality of the horrific drought. I don't want the summer to come, I don't want the rivers to be dry, I don't want the forests dying from beetle kills or from apocalyptic wildfires. Changes are coming to this beautiful valley that I don't really want to contemplate. I want it to thrive. But we'll see. The walls of rock will always be there no matter what happens, standing like sentries over the plants, trees, and animals on the valley floor below. Including the only slightly furry ape-like creatures running around in bermuda shorts with cameras in hand.

Tuesday, April 14, 2015

Incredible New Fossils Acquired for the Department! But...

During our field trip last weekend, we stopped briefly at a mineral show in the Sierra foothills. I wasn't going to buy anything, but then I saw some specimens that made my jaw drop, and they were available for an incredibly low price. I couldn't resist adding these beautiful pieces to my teaching collection at the college.

The first was a giant trilobite fossil from Morocco. Trilobites were ancient arthropods, among the first of the complex lifeforms to inhabit the Paleozoic seas. They had brains, eyes, legs, and survived in numerous different habitats. But most trilobites are very small, maybe an inch or two long. This monster was huge! And the seller was willing to part with it for only $30! I snapped it up.
I was headed back to vehicles when I saw the second incredible specimen. It was the tooth of a Mosasaur, one of the most terrifying predators in the Mesozoic seas. It was even in matrix, along with a fragment of the jawbone. And for just $12, how could I pass it up? Another specimen purchased.

Why the excitement over a Mosasaur? It's because they were one of the most interesting creatures ever found in our region. A local boy found the fossil in the foothills of the Coast Ranges just twenty miles or so from our campus. We've already acquired a skull of the 30-foot long creature for demonstrating our local paleontology finds.
An old dinosaur, along with a Mosasaur skull replica
I know some of you are already squirming just a little bit wanting to tell me that I was duped, and the fossils I purchased are fakes. Actually I already knew that. There's an old adage that if it's too good to be true, than it probably is. Producing fake specimens is an art that began just minutes after fossil collecting became "a thing" several hundred years ago. The trilobites and ammonites coming out of Morocco are particularly egregious examples. Genuine specimens have come from the region, but they are relatively rare and very expensive. Plenty of nearly worthless fragments exist, and people soon found they could mount partial and broken specimens in a matrix and sell them for a decent price. I imagine quite a few people have managed to eke out a living doing so.

If dealers were honest about such things, it wouldn't bother me too much. I wanted a large trilobite replica that I could use while discussing paleontology, and this specimen fit the bill pretty well. The ironic thing is that the dealer clearly marked some of his specimens of smaller trilobites as "copies", but he basically told me "why buy these smaller fakes when you could have the real thing right here for only $30?" As a replica, the price was pretty cheap. A genuine sample of this size could probably run into four figures, and sometimes these fakes carry such price tags. That's a pretty handy profit margin, courtesy of some poor uninformed person with too much money on hand.

The tooth is most likely the real thing, but was probably damaged on the back side. The root is probably left over from the faker's lunch, a piece of cow or sheep bone glued to the tooth. Sometimes they make entire jaw bones out of this stuff.
If you want to see our latest genuine fossil acquisition, here it is: plant fragments in a slab of sandstone. It's remarkable because it comes from the Western Metamorphic Belt of the Sierra Nevada, and metamorphic rocks don't often preserve fossils, but it happened here. It dates from the Jurassic period, a time when dinosaurs wandered the nearby landmass. Leaves and fragments of wood flowed into the nearby shoreline and came to be preserved in the sandy layers.

How do I know it is genuine? Well, I found it myself. That's the best way to confirm such things, and it's fun to boot.

For more information about these faked specimens, check out

Monday, April 13, 2015

Work Has Begun on the Yosemite Region Ferguson Slide!

I was up in Yosemite last weekend for a class field trip, and was surprised to see a lot of changes at the site of the Ferguson Slide, the huge 2006 slope failure that blocked Highway 140 for months. The road was covered with so much debris that bridges were needed to detour across the river and around the slide. That's been the status quo for most of the last decade. The detour is one way at a time, and a traffic signal slows up traffic into Yosemite Valley. That has been a great inconvenience for businesses in Mariposa that depend on the tourist trade. As I reported a few weeks ago, a final plan had been approved, and work was to begin on fixing things. It didn't take long!
A great many issues had to be considered before work could start. For one, they needed to know if the slide had stabilized, or if it was going to become worse. There were concerns at one point that an avalanche could completely block the Merced River and inundate the small village upstream. There was the river environment to consider. The Merced is a Wild and Scenic River, and major changes have legal ramifications. An extremely rare and endangered creature, the Limestone Salamander (Hydromantes brunus) is found only along the river in this area. Fewer than 2,000 are thought to remain in the world.
The final plan involves the removal of 100,000 cubic feet of debris, and the construction of a 750-foot-long rock shed that will allow future rockfalls to bounce harmlessly over the road and into the river. As I discussed the slide with my students from downstream (we couldn't see it yet), I wondered how they were going to remove debris from below without having more come down on them. The question was answered as we crossed the bridge and had our first look at the mitigation effort. The entire upper portion of the slide was covered by boulder containment nets to catch loose material that might tumble down.
As we drew closer, I couldn't help but notice the gigantic boulder in the middle of the netting, and the dirt road built across the slide, with some kind of equipment at the top. I found myself looking at a career choice I would not have felt comfortable with. I'd love to meet the person who is digging the slope with that spider dozer. That has to be a somewhat nerve-wracking job...
I've seen a slightly more dangerous version of working with rock slides, though. In 2009 we were on the road to Hana on Maui in the Hawaiian Islands. This is what the workers were doing there...

I'll be going up to Yosemite again in a few weeks, and will post reports as I see major changes.

Saturday, April 11, 2015

Driving Through the Most Dangerous Plate Boundary in the World: Geology's Junk Drawer on the Marin Headlands

We continue our drive through the most dangerous plate boundary in the world (past tense, since it became inactive 20 million-plus years ago), and we've arrived at the Marin Headlands, one of the most beautiful coastlines in the world, and a marvelous exposure of what I've called geology's junk drawer, the accretionary wedge of a subduction zone. The rocks of the wedge are called the  Franciscan Complex, and it's appropriate, given the chaotic nature of the rocks

We are taking a little detour from our drive from Point Reyes, and tooling about the headlands on Conzelman Drive. But even before that, I didn't want to miss a gem of a national monument tucked away in the depths of the headlands, Muir Woods.

Muir Woods preserves one of the small remnants of old-growth Redwood forest left in California. More than 95% of the original forests have been cut down, and the northern Coast Ranges have been deeply altered, and the ecosystems shredded. The native range of the Coast Redwoods and the extent of the Franciscan Complex correspond closely, but I don't think the relationship is necessarily biological. The trees need the climate afforded by the proximity of the Pacific Ocean, and the Franciscan Complex is a young rock unit that formed parallel to the same coastline.
As pointed out in the previous post of the series, the Marin Headlands are somewhat unique, having a higher than usual percentage of sea-floor ribbon chert exposures and the underlying pillow basalts of the ocean crust. As we start up the Conzelman Road, we get some marvelous views of the Golden Gate and the orange bridge that crosses it (see the top photo). In the parking areas people use to stare at the bridge, there are marvelous exposures of the chert and basalt.
The chert and basalt have been metamorphosed to some extent and deeply deformed, but the rocks still show much of their original nature. In some of the roadcuts, the chert can be seen lying directly on the sea-floor basal. Geologists have figured out that the sequence preserves about 100 million years of deposition (from 200 to 100 million years ago). This is an extraordinarily long record of slow travel of the plate across the Pacific Ocean.
The scenery is extraordinary along the road. The Golden Gate rises out of the sea in bold cliffs, and though the headlands have been altered by road-building and military activity, the region today exudes beauty and serenity.
Wait, what? Military activity on these beautiful cliffs? Why?

When World War II was being fought, San Francisco Bay was one of the most important strategic strongholds for the entire Pacific Theater of operations. There was the harbor itself through which much of the fleet operated, factories and ammunition depots, and the inland agricultural areas. That and a huge civilian population. The hills above the Golden Gate were studded with huge cannons and guns that could wreak devastation on any enemy flotilla that tried to enter the harbor. Below is Battery Mendell, just north of the Point Bonita Lighthouse.
The Marin Headlands region is a stunningly beautiful place with a fascinating geological story. The area is protected as part of the Golden Gate National Recreation Area, which is more or less equivalent to a national park. It is certainly a popular destination, but it's usually possible to find some quiet corners, especially if you are willing to hike a little. In our next post, we'll head down to the beaches of the Marin.

Friday, April 10, 2015

Solar Pillar from the Foothills of the Sierra Nevada

We were headed home after a brief excursion into the Sierra Nevada foothills, and as we enjoyed the colorful sunset we noticed a solar pillar (or sun pillar). The pillar is caused by light reflecting off of ice crystals in the upper troposphere (the part of the atmosphere that we live in and where most weather occurs). It's maybe not the most vivid ever seen, but they always catch my attention. Now, if we could just get the auroras down south into California tonight!

Monday, April 6, 2015

A Fleeting Spring in the Sierra Nevada Foothills: The Red Hills Area of Critical Environmental Concern

There was actually a bit of rain today in central and northern California. It wasn't much, barely getting the ground wet in the valley, and maybe a quarter of an inch in the Sierra Nevada foothills, but it was the first storm in many weeks, and there is a promising storm rolling in on Tuesday. Not a drought-breaker, but it will be one of the few cold arctic storms we've had all winter, expected to drop as much as foot of snow at higher elevations. Again, not nearly enough, but a brief respite from the unseasonably warm weather of the last two months.
We headed into to the foothills for a brief look at the spring wildflowers. There weren't many expected, so we weren't disappointed, but there were a few patches here and there of color, and if I held the camera just right, it could look like a normal spring bloom. But the dryness lies beyond the edges of each flower picture.
The Red Hills Area of Critical Environmental Concern is a several square mile area owned by the federal Bureau of Land Management. For years it was ignored, and used for dumping, shooting, and off-road vehicle travel. Somewhere along the line, someone realized that the serpentine soils of the "wasteland" were harboring a large number of rare and endemic species of plants and animals. The rock was the reason. Serpentine is the metamorphic product of peridotite, an olivine-rich rock more normally found deep in the Earth's mantle.
When the rock weathers to soil, the soil is poor in some critical nutrients, and overly rich in some metals that most plants can't tolerate. Among these plants are the invasive grasses that have overwhelmed many other ecosystems in California. Oaks don't grow well in the soils either. The lack of grass allows the serpentine-tolerant plants to thrive, at least when there is water.
Golden Poppies and Monkey Flowers do especially well, along with several varieties of Lupine.
The soil was very dry and the few flowers that were able to bloom this year were already fading. I hope the big storm Tuesday helps a little. The bugs need a hand.

Sunday, April 5, 2015

Driving Through the Most Dangerous Plate Boundary in the World: Welcome to Geology's Junk Drawer

View from Muir Beach Overlook towards the Marin Headlands

I'm pretty sure every household has a junk drawer. It's that place where objects that we can't or won't get rid of accumulate. It's a mixed up drawer full of screws, paperclips, old receipts, coupons, expired credit cards, coins...they all end up collected in that one place. And even in the most organized of households, this is the one place where chaos reigns supreme. There is a similar kind of place in the Earth's crust.

One of the great intellectual leaps in the science of geology was the recognition that the Earth is organized, that there are geological processes that follow certain natural laws. Principles like superposition, lateral continuity and original horizontality allowed the early geologists to decipher the geologic history of a region, leading to the first "golden age" of the science in the early 1800s. From the careful analysis of the stratigraphic relationships in a given region, earth scientists were able to construct the geologic time scale, and solve some hugely mysterious problems about how the crust of the Earth operates. They were finally able to understand the origins of most kinds of rocks.
Melange deposits along Highway 1 just north of the Marin Headlands

But then geologists came to California, and all the rules seemed to get tossed out the window. While some rock sequences in the state followed the "rules" and formed decipherable sequences (in the Basin and Range Province, for instance), in other places the rocks made no sense at all. In parts of California's Coast Ranges, sequences of rocks were exposed that were upside down, and so chopped up by intense faulting that the layers couldn't be followed for more than a few hundred yards. The continuation of these layers couldn't be found. Rocks showed evidence of extreme depth of burial, 15 or 20 miles, and yet showed little evidence of having been heated to any great extent (the Earth is hot enough in many parts of the crust to melt rocks at much lesser depths).

Most of the time, geologic mapmakers define "formations" and "groups", well-demarcated strata that can be mapped, and be clearly distinguished from adjacent layers. They construct geologic maps of these rocks. But faced with the strange rocks of the Coast Ranges, they more or less threw up their hands and called these chaotic rocks the Franciscan Complex. And "complex" was right. There was an entire region on the geologic map of California given over to a disorganized mess of rocks that could barely be subdivided any further (it's the blue stuff on the map below). The rocks found in the complex include a clay-rich sandstone called graywacke, dark colored shale, pillow basalt, serpentine, deep-ocean chert, and the occasional volcano or coral reef.

Geologists had discovered geology's junk drawer.
It wasn't until the theory of plate tectonics was developed (and accepted by the geologic community) in the 1960s that the origin of the Franciscan Complex could be at least partly understood. The outer shell of the Earth called the lithosphere (composed of the the continental and oceanic crust as well as the uppermost part of the mantle), slides slowly over the nearly molten layer in the mantle called the asthenosphere. In some places, the lithosphere splits open, producing volcanic eruptions and new oceanic crusts. These are divergent boundaries. At convergent boundaries, the crust comes together and is destroyed, either by crumpling upwards into high mountain ranges, or by one plate sliding beneath the other at subduction zones. At transform boundaries, the plates of the lithosphere slide past each other. The subduction zone is the site of the largest earthquakes and most intense volcanic eruptions on the planet. They are the most dangerous plate boundaries in the world. Luckily, the subduction zone in central California is extinct and erosion has exposed its interior parts. That's why we are on this driving journey through the old subduction zone.

I've spent the first part of this blog series on the other side of California's transform boundary, the San Andreas fault. Driving south from Stinson Beach, we now reach the rocks of the Franciscan Complex on the Marin Headlands.

The trenches of subduction zones are the collecting place for sediments of the deep ocean as the crust slides into the mantle. Volcanoes and associated coral reefs are sometimes scraped off as well. Sandstone, silt and shale eroded from the nearby continent will also accumulate in the trench. The large chaotic wedge-shaped deposit is called an accretionary wedge.  The Marin Headlands include some of the less common rocks of the Franciscan Complex, ribbon chert and pillow basalt (green and orange on the map above).
NPS geologist William Elder discussing pillow basalts of the Marin Headlands near Point Bonita

The pillow basalts of the Marin Headlands formed at a divergent boundary around 200 million years ago, perhaps more than a thousand miles away, close to the equator. Lava erupting onto the seafloor produces the distinctive lobate shapes that are about the size of down pillows (but are considerably harder!).
Ribbon chert of the Franciscan Complex on Conzelman Road on the Marin Headlands
As this ocean crust moved on its long journey towards California, small single-celled creatures called radiolarians lived and died in the ocean waters above. As they died, their silica shells sank to the seafloor, slowly accumulating in dense layers of the quartz-rich rock called chert. They formed into distinctive layers about an inch thick, separated by thin layers of clay. The layering was about the thickness of ribbon, giving rise to the name "ribbon chert".

We'll have an exploration of the Marin Headlands in the next post...