What to do on a Saturday? Let's Go to the Middle of the Earth (via Del Puerto Canyon)!

The strange and alien landscape in upper Del Puerto Canyon.

California has some really strange landscapes. A state that has beaches, mountains, volcanoes, forests, and deserts is going to offer many perspectives of the complex geological influences on the state. But for alien and otherworldly, few places in the state can compare to the journey you take when you follow Del Puerto Canyon from its mouth in the Great Valley to the headwaters in the Diablo Range. It's a journey into the middle of the world. Our Geology Club made the trip a few weeks ago as an ending of the semester celebration. Odd way to celebrate? Did you simply party? We traveled half-way to the center of the planet!

"Del Puerto" refers to "The Gate", the constriction of hard sandstone at the mouth of the canyon.

I guess I should be a bit more specific. We journeyed to rocks that had once been part of the Earth's mantle, the 1,800 mile thick layer that lies just beneath the thin crust (3-50 miles thick). We couldn't reach the core of the planet, because no one can (despite sci-fi movies that say otherwise). Since mantle rock is very hot and is subject to convection, it is at least conceivable that the rocks we explored had once been close to the Earth's core.

So how does one explore the Earth's mantle? Well, first one has to get through the crust, and the thinnest crust is that which makes up the ocean floors. It's nominally composed of basalt, but the details are more complex.

In Del Puerto Canyon, the ocean floor is covered by...a bit of sediment. About 25,000 feet of it! The sediments poured off the mountainous edge of the continent during the later part of the dinosaur era, the Cretaceous Period. There was a huge subduction zone that formed as oceanic crust plunged into the mantle beneath the edge of the North American continent. This so-called Cascadia Subduction Zone caused volcanoes to form where the Sierra Nevada is today, but the area offshore of the volcanic arc, the forearc basin, collected sediments. As the sediments accumulated, they pressed the crust downward and even more sediment piled on top. Eventually the layers reached a thickness of five miles.

The basin collected fossils as well. There were the usual shells of clams, snails and ammonites, a variety of shark teeth, and three groups of seagoing reptiles, the plesiosaurs (think Loch Ness), ichthyosaurs (think reptilian version of a dolphin), and 35-foot-long mosasaurs (think "swim for your life!"). Even dinosaur fossils have been found. The first dinosaur ever found in California, a Saurolophus, was discovered in the lower reaches of Del Puerto Canyon in 1935.

Eventually, one will reach the base of the oldest sediments, and encounter the ocean crust itself. Faulting obscures some of the relationship, and so in the picture below we see some of the oldest sediment on the right (somewhat brownish shale) and basaltic/andesitic volcanic rock on the left (greenish gray), separated by a fault. The volcanic rocks are harder, and the canyon takes on a more rugged aspect as we climb higher into the mountains.

The Coast Ranges of California are one of the youngest mountain systems in the world, having been uplifted mostly in the last 3 million years or so. The streams in this dry environment have not been able to downcut as fast as the mountains are rising, so they flow much of the way over bedrock. There are few floodplains in these mountains.

The water flows almost year-round and thus the canyon is a critical habitat for all kinds of wildlife. Dozens of mammals and reptile species are known, and nearly 200 bird species have been observed here.

Oceanic crust is basaltic in composition, but there are differences at depth. On the ocean floor, basalt flows form "pillows", globular masses of the volcanic rock. Beneath the pillow basalts, basaltic dikes fed the eruptions. Dikes occur when volcanic rock fills cracks and fissures in the surrounding rock. Since the surrounding rock is also dike material, the entire layer, a mile or two thick, is made of vertical sheet dikes. Feeding these dikes were magma chambers composed of...basalt! But some of the basalt was left at the base of the oceanic crust where it then cooled slowly to form a sparkling crystalline rock called gabbro. The entire suite of rocks is called an ophiolite sequence. The Coast Range Ophiolite sequence in Del Puerto Canyon is considered to be the second best exposed in the state, behind the Point Sal Ophiolite in southern California.

We stopped in one of the most rugged parts of the canyon to investigate the gabbro where it was pierced by a vein of quartz (below). People have looked for gold here, but I doubt they found any.

Just a few more miles up the canyon and we penetrated the uppermost part of the mantle. The rock originally consisted of ultramafic minerals like olivine and pyroxene, but here the rock has been metamorphosed into serpentine, California's state rock. The rock was sheared and faulted on its way to the surface, leaving shiny green and black polished surfaces (below).

And then we were there. In the uppermost part of the canyon, we reached the netherworld of mantle rock that was far less altered, so that it retained some of its original appearance. In places we could see olivine and pyroxene crystals, as well as grains of chromite. These ultramafic rocks contain few nutrients needed by plant life, so only a few species can tolerate living on these slopes. Gray pines are among them, grasses generally are not. There are a number of wildflower species endemic to California that can be found here.

Looking at these shattered broken rocks from very deep in the Earth, one imagines hell freezing over. The forges of the demons and devils lie frozen in place, to be slowly removed by earthly weathering. They tried to invade the surface realm, but they were defeated by the forces of the heavens, the water and ice falling from the sky.

It may have been a metaphorical battlefield, but in the end there is great beauty in the rarity of the flowers, plants and animals that thrive, or at least tolerate the conditions in the upper canyon.

We turned around and headed back to more familiar habitats.

Del Puerto Canyon is traversed (slowly) by Highway 130, originating in Patterson on the floor of the
Great Valley. It can also be reached by way of Mines Road out of Livermore, or  a winding road out of the San Jose area over Mt. Hamilton and the Lick Observatory complex. It is not a fast way to go!

Up Close and Personal with a Western Tanager

Seasoned birders won't be surprised at the excitement a rank amateur like myself feels the first time he or she sees an interesting bird up close. Western Tanagers (Piranga ludoviciana) are relatively common forest and woodland birds across the western United States and Mexico and I'm sure they are seen often by the experts.  I've only been seriously seeking out new species for the last five months, so I still get to experience the joy of seeing something new and different on a fairly regular basis as I add to the list of observed species.

I've known about Western Tanagers for a long time, but I've never been close enough with an adequate camera to actually get decent photographs of one, but that changed today. We were exploring the upper reaches of the Stanislaus River in the Sierra Nevada of California, and as I was driving down the Clark Fork Road at the end of the day, I saw a flash of yellow out of the corner of my eye. I hit the brakes, hoping against hope that I wouldn't spook the brightly colored male.

He didn't spook. I snapped a few distant shots, and then backed up the car hoping to get closer (I know that sounds like an odd way to do it, but from only forty or so feet away, getting out of the car would have spooked it more, I think). He hung around, as if he was observing me (a large rival in his territory?).

The tanagers are a large and diverse group of passerine birds centered mostly in the American tropics, but the Western Tanager ranges farther north than any other species, as far southern Alaska. For being so brightly colored, they are not often seen, as they tend to hang out in the upper canopy of the forest. I felt privileged to spend a few minutes observing this one, from basically all angles. Was he sending me a message with this last shot?

Brightly colored birds often carry the seeds of their own destruction because their feathers may be in high demand for one reason or another. Looking at the tanager reminded me of the large number of species of Honeycreepers that once existed in the Hawaiian Islands. A few of them are still hanging in there (two out of the original 51 species), but most of the others are extinct or nearly so, in part because Hawaiian royalty centuries ago demanded robes made out of their brightly colored feathers (habitat loss, malaria, and competition with invasive species and predators were major factors as well). The tanagers, with their wide range across all the western states avoided such a fate, but they were for a time considered agricultural pests and were poisoned or shot. They are protected today, and their numbers have grown to where they are a "species of least concern".

It was a privilege to see one up close and personal today.

PS: Mrs. Geotripper took a short video of the same bird...

A Convergence of Wonders, Day 12: A Richness of Geologic Drama at the Grand Tetons (and Pelicans!)

Our continuing journey through the Pacific Northwest and the Northern Rocky Mountains, the Convergence of Wonders, reached the twelfth day. We woke up in our Colter Bay campsite and set out to explore Grand Teton National Park.

The Tetons are in the Rocky Mountains, but they are not of the Rocky Mountains. The rocks are right, but not the origin of the peaks themselves. Most of the mountains we visited since leaving Washington were the direct result of convergent tectonics, that is, the result of subduction along the west coast of the North American Continent. The forces involved are usually compressional in nature, but the Tetons are the direct opposite. They form because the earth's crust is extending; it is being ripped apart.

But first, the pelicans! We stopped at Jackson Lake Dam to have a look around (the picture above was taken from on top of the dam), and could see dozens of white things floating in the rushing waters below the dam. A zoom shot revealed the objects to be American White Pelicans. I suppose they get good fish at the outlet.

We then drove to the summit of Signal Mountain to get one of the best views of the Grand Teton region. The Tetons have an interesting glacial history. Where Yellowstone was covered by an ice cap, most of the Tetons were dominated by alpine glaciers confined to mountain canyons. Some of the Yellowstone ice cap flowed to the south around the base of Signal Mountain, so the most notable features at our feet included the Potholes, a group of kettles and kettle lakes left behind by stagnant masses of ice (below).

We had a stunning view of the Teton crest and Jackson Lake from the peak of Signal Mountain (although I think some of the students missed the view as they tried to get a signal on their cellphones).

We then headed out of the park briefly and crossed the swollen Snake River. All the rivers we saw this trip were very close to flood stage, and even now in late July they apparently are still running high and cold.

Our destination was a little east of the park in the canyon of the Gros Ventre River. Most visitors to Grand Teton National Park never go out this way, and they miss one of the remarkable geologic sights in Wyoming: the Gros Ventre Slide.

A series of Paleozoic sedimentary rocks are found in the area; the layers sloped north into the valley at about 20 degrees. Tensleep sandstone was exposed at the surface, and was underlain by much weaker shale and mudstone. Weeks of heavy rain had destabilized the rocks, and on June 23rd, 1925, a large mass nearly a mile long and 2,000 feet wide gave way and slid into the valley. It had a volume of around 50 million cubic yards.

The avalanche produced a debris dam more than 200 feet high. The Gros Ventre River began filling the new "reservoir". It was two years before the dam filled, and when the water breached the top of the dam on May 17th, 1925, the weakness of making dams out of loose debris became immediately apparent: the rushing waters tore away at the top of the dam, and much of the lake emptied into the riverbed below. Several miles downstream, the town of Kelly lay unprotected. The resulting flood killed six people and the town was washed away.

 A ghostly forest of dead trees can be seen standing in the middle of the lake.

We noticed a ranch road that crossed the debris field, so we checked it out. Huge boulders of sandstone were scattered all about. It was an eerie sight. The flooded river was pouring through the outlet of the dam, and we remarked how crazy it would be to go rafting on such a raging river. Then, of course, two kayakers made their way under the bridge and headed downstream. We sort of kept an eye on them for a few miles downstream. They apparently survived...

The road back into the park provided spectacular views of the mountain crest.

Flowers were blooming all across the Antelope Flats area. The fault line that produced the mountains has moved the mountains upwards to heights of 13,000+ feet, while the valley floor has at least 10,000 feet of sediment filling it in. The fault has moved some five miles in the vertical sense!



Our next destination was Jenny Lake, which formed behind the terminal moraines of glaciers flowing out from the mountains. It is a beautiful (and very popular) starting point for a number of hikes. I gave the students one of their very precious and rare half-days to hike or do showers/laundry (or, hopefully all of the above).





I headed back to camp, but had to stop and photograph a beautiful Western Tanager hanging out in a tree along the trail. The males are obviously very colorful!

The moraine that dammed Jenny Lake was also covered with beautiful flowers.

After dinner, we went on a moose-hunt in the twilight, and saw a moose at great distance, but more impressive was the serene sunset reflected on the Oxbow Bend of the Snake River. The next day we would be starting one of the long driving days making our way back home. There were just four days left on our journey. The story will continue in the next post.