Strangers in a Strange Land: The Value of a Road Cut

As teachers, we hope to go in the field with our students in hopes that they can related cartoons in a textbook with exposures in the real world.  Then we get there, and we find together that sometimes the "field" does not readily give up secrets. There is this phenomena called "weathering" that renders rocks indistinguishable from other rocks. Take the above scene, from an area near Shoshone, a little village east of Death Valley National Park. If we were back east somewhere, there would be a complete covering of green organic material that biologists call trees and shrubs covering most of the rocks, rendering identification and interpretation practically impossible (and believe me, I appreciate and admire those who figured out the story of places like the Appalachians and the Canadian Shield).

But even here, where the climate is so dry that plants can scarcely survive, the rocks are still obscured. The geologists who have training in field methods can make sense of this sort of landscape, but students who are in the field for the first time can feel intimidated. A few gray rocks in the foreground, some tan colored rocks across the small valley, and a difficult time understanding how they relate to each other. It would be a challenge. But once in a while, the department of transportation does us a real favor. They want to make their roads straighter, and when nature hasn't cooperated by eroding into straight lines, they make roadcuts for us.

For instance, if the scene shown above doesn't look all that remarkable, look what happens when you turn around...

That's an outcrop! This is one of those sweet times when the real world looks a lot like the textbook diagrams, so the students get to do some basic interpretation of rock relationships without having to visualize obscured contact lines. Many field trips visit this outcrop, so much so that the department of transportation has left behind a parking area across the street that is big enough to accept even buses.

So, what would you do with your students here?

Oh, and by the way, all you mineralogists out there, what do you think this nice botryoidal mineral might be? I have my strong suspicions about a relatively simple answer, but I've just assumed it for a long time. The host rock is a rhyolite tuff, and hot vapors and groundwater have probably both influenced the outcrop.

Strangers in a Strange Land: The long journey of a sea lily

The larva emerged from the egg and began drifting in the gentle current. It was a bilaterally symmetrical body that recalled a small chordate, but it wasn't. The ciliated body allowed it to swim to some extent but within a few hours it settled to the sea floor and a remarkable change occurred. It began to develop an odd five-fold symmetry. That placed the organism in the lineage of the phylum echinodermata.

Attribution: Pacific Ring of Fire 2004 Expedition. NOAA Office of Ocean Exploration; Dr. Bob Embley, NOAA PMEL, Chief Scientist: http://www.flickr.com/photos/noaaphotolib/5114735036/in/photostream/

Over time the organism developed a stalk with a root-like holdfast, and a flower-like "head" on top. As much as it looked like a plant, it was indeed an animal. The "flower" was a food collecting organ with feather-like appendages that captured small bits of food drifting by in the currents. The edible particles were transported to the mouth at the center of the "flower" and consumed. The stalk gave the organism an advantage over bottom dwelling filter feeders by extending above the other benthic species. These crinoids, also known as sea lilies, were hugely successful in their time, with thousands of them anchored to some parts of the ocean floor, waving like a field of wheat at the bottom of a warm tropical sea.

This particular individual lived for several years, but during a tropical storm the turbulent water broke the stalk off, and the calyx sank to the seafloor and the crinoid died. The calyx broke into numerous calcite plates, and the organism was added to the remains of thousands of crinoids that had died before. In time the bits of stalk and little platelets were buried under the constantly accumulated debris from crinoids that were born much later. Over time the water was mostly squeezed out and the crinoid debris began to lithify, that is, it turned to solid stone. More sediment covered the limestone, providing additional pressure, and soon the remains of the small crinoid were pretty much removed from the effects of surficial processes. Then came the vast void of time. For more than 100 million years, the crinoid stalk simply existed, pretty much without change, other than a very gradual buildup of pressure as the rock was buried ever deeper under thick sequences of sand, silt and limestone.

Time ebbs and flows. Sometimes things happen very quickly, but in other situations time seems endless. The crinoid lived for only a few years, but it lay buried for millions. In this kind of immortality, sentience would be a curse. Entombed in total darkness and silence for endless millennia, insanity would be a blessing. Time wore on, and the only indications of activity were the occasional earthquake and slow change of orientation and temperature. It was also getting hotter, for big things were happening above.

The ocean had disappeared, and the rocks that had lain at the bottom of the sea were now pushed up into a mountain range. Out to the west, a subduction zone had developed, and the resulting compressional forces had buckled the rocks into a series of folds and thrust faults. A few tens of miles away, vast bodies of magma were intruding into the overlying rock, although the fragments of the crinoid were not directly effected by the igneous activity. They remained entombed in the darkness, and over time the mountains above were smoothed by erosion to a fairly muted landscape of low hills.

More millions of years passed, but the pace of change increased. There were more earthquakes, and there was an imperceptibly slow change in the amount of pressure. One day there was a crack as the stressed rock relaxed by fracturing. And then again. And then, for the first time in millions of years, water started seeping through the small fractures. The water was not salty; it was groundwater coming from rainstorms far above. Sound became more perceptible; thunder and the shattering of stones rolling down a hill.

One day, light appeared as a rock fall exposed the bit of limestone encased in what turned out to be a high cliff. A short time later, the limestone bearing the fragments of the crinoid fell out of the cliff onto the talus slope below. After the insanely slow pace of change over millions of years, events were now dazzlingly fast. One afternoon, a particularly intense thunderstorm produced a mudflow that tore away the base of the talus slope, and the chunk of rock containing the crinoid was lifted and carried in a slurry of rock and fine-grained sediment. This one storm only carried the boulder a few hundred yards, but the next storm and the one after carried the rock for several miles out onto an alluvial fan.

The rock sat, exposed to the occasional rainstorm, the endless heat of the blazing sun, and the growth of small shrubs and perennials. The surface of the rock became etched, and the structure of the original crinoid stem became obvious, enough that a semi-sentient being perceived that the one stone was different than the others nearby. He picked it up, considered the nature of the once living organism, snapped a picture, and laid the stone on the ground again. He wandered off.

300 million years after the small crinoid lived and died, the last vestiges of its existence would soon dissolve away, and its constituent atoms would be distributed through the soil. It will soon be gone.

And that is the story of the crinoid I found last month.

I've always thought about rocks this way, but in presenting the narrative in this style, I was no doubt influenced by The Planet in a Pebble: A Journey into Earth’s Deep History by Jan Zalasiewicz, which I reviewed a while back. Strangers in a Strange Land is my series on the geology revealed during a series of trips to Death Valley and the Mojave National Preserve in February and March.

Strangers in a Strange Land: The Largest National Park in the Lower 48

The travelers who were the Strangers in a Strange Land had reached the end of the day, and had crossed the boundary into Death Valley National Park quite a few miles ago. We were looking at an astounding desert valley, with high snow-capped mountains in the distance, vast fault scarps, wide desert playas, and deeply carved desert canyons.

In the geologic sense, Death Valley may very well be the most diverse national park in our country. It has some very old rocks, possibly dating back as far as 2.5 billion years, and rocks that formed in just the last few hundred years (at Ubehebe Craters and on the Badwater salt flats). More extraordinary than the range of ages is the completeness of the rock record. The park has Archean and Proterozoic rocks, it has some of the thickest Cambrian rocks to be found anywhere, it has rocks from every period of the Paleozoic era, and though not as widespread, it has rocks from the Mesozoic era as well. Paleogene and Neogene periods of the Cenozoic era are represented by beautiful sequences of terrestrial sediments, especially in Titus Canyon and near Furnace Creek. Just the one picture above includes Neogene basalts, Jurassic-Cretaceous granites, Paleozoic carbonate rocks, and Holocene sediments.

Death Valley also packs in some big extremes. The relief of the park (the difference between the highest and lowest point) is about extreme as it gets, more than 11,000 feet. There are some seasons in the year when one can be baking in 100 degree plus heat on the valley floor, and find relief by standing in the snow on the flanks of Telescope Peak (above).

The Late Proterozoic-Paleozoic rocks, such as those seen in the Cottonwood Mountains above, have a total aggregate thickness of more than four miles! And for desert landscapes, Death Valley is unrivaled. Not the stereotypical saguaro cactus type of desert, but evidence of erosion and deposition in an extremely dry landscape. Sand dunes, alluvial fans, bajadas, playas, and pediments are well-represented. And tectonic activity: faults, folds and unconformities are found all over, starkly exposed in the vegetation-challenged landscape (that's not saying "no plants", as the park also hosts a huge number of plant species; they just don't cover everything).

Did I mention that the park is big? It's really big, covering more than 3 million acres, making it the largest national park in the lower 48 states (and also Hawaii). Just how big is that? Death Valley itself is more than 100 miles long and 15-20 miles wide. But it is just a part of Death Valley National Park.

All the pictures that I took of this long impressive valley were taken in Death Valley National Park. But you haven't even seen Death Valley yet. This is the Panamint Valley, a spectacular desert valley in its own right, which was added to the national park in 1994. Those are the Panamint Dunes in the picture above.

We had another major pass to traverse before we could enter Death Valley itself. By the time we arrived at Furnace Creek, the sun was down. We would continue our exploration the next morning...

A Priceless Collection of Minerals: To see, or not to see

I was in the field yesterday with my students, and one of our stops was at the California State Mining and Mineral Museum in Mariposa at the south end of the California Mother Lode. I am offering up a selection of photos of some of the finest mineral specimens you will ever see anywhere, but I hope you will read to the end of this post as you look at them. Enjoy!

The first few images are some of the striking specimens of crystalline gold. Gold crystallizes in the isometric crystal system (three equal axes at ninety degrees), but the crystals themselves are rarely seen because gold is so malleable that the structure is lost the moment the mineral rolls in a stream.

Gold crystals, then, instead of gold nuggets. They are just gorgeous, and priceless, because the vast majority of crystal specimens were melted into bullion along with all the other gold during the gold rush days, even the biggest single nugget, one that weighed close to 200 pounds.

 You just don't expect gold to look like this.

Or this...when the Harvard open-pit mine was operating in the 1980's and was about to close down, the miners hit a rich pocket. Mine employees who had hardly ever seen even a small bit of gold in the disseminated ores were surprised to see a 60 pound chunk of gold pass by on the conveyor belt. It was composes of leaf gold, a crystalline variety composed of...um...leaf-like flakes of gold. The entire mass was preserved and can be seen at the Ironstone Winery at Murphys, but a large flake can be seen above.

And then there is the Fricot Nugget. The 13.6 pound nugget is the largest single gold mass preserved from the Gold Rush Days, having been discovered in 1865. It lay a long time in a safe deposit box, almost completely forgotten. It came to the state collection in 1943.

An exceedingly rare mineral is a beautiful blue sapphire-like gem called benitoite. It is found at a single mine in the California Coast Ranges. It was designated the California state gemstone in 1985.

The sample below includes two very rare minerals. The black mineral is neptunite, which is often found in association with the benitoite.

Another unique mineral assemblage in California comes from the pegmatite veins in San Diego and Riverside counties. These veins contain immense crystals of quartz, feldspar, muscovite mica, and a group of rare gemstones, most notably tourmaline. For a time in the early 1920's tourmaline was the most prized gem in China, and many incredible crystals were exported.

Other minerals came to the state from all over the world. Below is a striking example of beryl (aquamarine), a relative of emerald.

And sulfur crystals deposited on aragonite crystals...

And some beautiful crystallized azurite and malachite, ores of copper.

And opal from the Virgin Valley in Nevada...

Another example of pegmatite contains a form of feldspar called amazonite.

Some more spectacular azurite crystals.

The crystals below are wulfenite, an important ore of molybdenum and lead.

And finally, the museum has an excellent exhibit of meteorite specimens, including this cross-section of the crystallized elemental iron of the Giant Goose Meteorite, which fell in Modoc County in 1938. The original weighed over a ton.

Wouldn't you just love to see these incredible rare specimens for themselves? I can assure you that it is a great exhibit, quite worthy of a short diversion on your way to Yosemite National Park. But you don't get to see them. You may never get to see them ever again. Why? Because the California State Mining and Mineral Museum is on the state closure list, one of 70 parks to be closed and shuttered because of cuts of $22 million to the state park system, approximately 70 pennies for each inhabitant of the state. I am incensed that the people of our state legislature are so incredibly short-sighted as to allow this to happen.

I feel hopeless sometimes at the stupidity I see. State parks generate economic activity, they don't drain it. Closing these parks makes no sense at all. Mitchell Caverns has already closed, and vandals have already done grievous damage. It will cost so much more to re-open these parks once they have been degraded. And yet that is what our government has decided to do, come June. I don't quite know what would work to change this, but one can start by letting your legislators know how you feel about this. The parks have few friends in the legislature obviously, but the politicos might listen to someone besides their ever-present lobbyists if they heard from their constituents. Who knows? There is a facebook page for the California State Mines and Mineral Museum, and there is the California State Parks Foundation, the best place to get information on how to proceed politically.

I know that blogs are places for the writing of many words, but I have few enough words that can express my disgust at the members of the state legislature and government for allowing this to happen.

Strangers in a Strange Land: A River Runs Through It, or at least used to

"After three days in the desert fun
I was looking at a river bed
And the story it told of a river that flowed
Made me sad to think it was dead"

from A Horse with No Name by Dewey Bunnell

Oh, the songs of our youth. A Horse With No Name by America came out in the olden days of 1972, and was one of those songs that imprinted itself into my junior high psyche in such a way that it can never leave. I think they call it an earworm, known to drive people nuts, but it is a pleasant one for me. It was a bit of an anthem for us backpackers and young desert rats. The lyrics from the song popped into my head as we pulled up to the next stop on our Strangers in Strange Land tour of Death Valley and the surrounding desert region of eastern California.

For first-time visitors, pretty much everything about the desert is strange. For first year geology students, the mystery is deepened by that little bit of extra knowledge they possess that has them observing the rocks and surrounding mountains, trying to understand how this landscape might have developed.

So what was going on here? We had arrived at the eastern foot of the southern Sierra Nevada and parked in the midst of a lava flow from a cinder cone in the Coso Volcanic Field called Red Hill. The age is not precisely known, but it probably is less than 130,000 years old. The lava flow is covered by tan colored eolian (windblown) dust. Up to this point nothing seems particularly strange, but in the picture above, one can see a gap at the edge of the lava flow, a little bit to the right. Why is it there?

Having walked a quarter mile over rough lava surfaces, it was a bit of a surprise to come across this sage covered flat area that seemed to be composed only of sand and silt, with only a few scattered boulders of the basalt. Something was a bit off about this part of the lava flow.

A look ahead confirmed the odd nature of this stop (below). The lava flow had turned into an intricate labyrinth of deep holes and channels. Even if you barely know anything about lava flows, it is clear that lava doesn't do this sort of thing. This lava has clearly been scoured by a pretty large river, the deep rounded pits being potholes formed by swirling masses of pebbles and gravel. The name of our stop, Fossil Falls, more or less supports the contention that a river once flowed here.

But this is a desert. No rivers are found nearby, and the few streams that flow off the nearby slopes of the Sierra Nevada sink quickly into the gravel-rich alluvial fans long before reaching this site. Could the channel be the result of flash floods? It doesn't seem likely, because the channel upstream has not been cleansed of the easily eroded silt and sand for a very long time. The growth of brush in the old channel suggests stability.

There is a story here...until the 1920s, a large natural lake existed just north of Fossil Falls. It was called Owens Lake, and it was the natural sump for most of the streams and small rivers flowing off the eastern flank of the Sierra Nevada. Although the lake covered an area 8 miles by 12 miles, it was usually no more than 30 feet deep, and in the intense desert heat the water left only by evaporating. There could be no outlet unless the water reached a depth of 200 feet or so. If it spilled over the water would be directed downstream right towards Fossil Falls. The lake is mostly dry today because Los Angeles has diverted the water than once flowed into the basin.

Where did all the water come from? Clearly at some time in the past the climate was cooler and wetter than it is today. The glacial ice ages that affected the region during the last two million years provide a reasonable explanation. Glacial meltwater flowed through Mono Lake and the Owens River, filling up Owens Lake which in turn spilled over into other lake basins farther to the south. These bodies of water are called pluvial lakes.

The potholes are still active today, but in a different way. The rare precipitation events will occasionally leave water standing for weeks in some of them. The silt in the bottom contains the desiccated eggs of small delicate fairy shrimp. When they get wet, the shrimp hatch and grow quickly to maturity in a race to produce eggs before the pothole is dry again. I found a few of them warming up in a small pool that still contained water despite the dry year.

Still, seeing the ghosts of long gone and forgotten rivers is sort of sad. There is no crashing of water cascades, just the quiet breezes (or gales, if a storm is blowing through).  But there was a previous trip...2005 was a very wet year, and we were following on the heels of a major storm. When we reached the falls, I heard something I had never heard before. Water flowing in the ancient gorge! There was no mistaking these chocolate colored trickles with the big ice age rivers, but it was impressive to see anyway.

This is the joy of teaching geology! From small inconsistencies in a landscape come grand stories of climate change, glaciers, vast freshwater lakes, and fertile ground for the curiosity and imagination of our students.

paleomagnetism in rocks that provided unexpected proof of plate tectonics. James Hutton staring at a Roman fortification in Scotland that led to the recognition of geologic time. Nicolas Steno studying "devils tongues" and discovering the biologic origin of fossils.  Geology isn't just an academic discipline; it is an adventure pretty much like no other.

Fossil Falls can be found a few miles south of the Coso Junction Rest Area on Highway 395. Turn east on Cinder Road (just south of Red Hill, the prominent cinder cone next to the highway), and follow the signs on the gravel road about a mile to the recently improved parking area and trailhead (vault toilet and picnic tables available, and a small primitive campsite).

A Half Dome Day in the Central Valley

 We don't get many of them. One might think that living a mere five miles or so from the Sierra Nevada foothills that the range would be an awesome backdrop to the valley floor, in the way of the Rocky Mountains and Denver, or the Sandia Mountains behind Albuquerque. But it is not at all like that.

The Sierra Nevada in structure is essentially a huge tilted block of granite and metamorphic rocks about 400 miles long and 40-50 miles wide. The gentle slope is on the west side, so the high crest (which reaches 12,000-14,000 feet in elevation) is around 50 miles away as the crow flies from where I live.

An additional problem is air quality. Our fair valley (we actually call it the Great Valley) is completely surrounded by mountains, so the air is usually trapped and pollutants build up ominously. Dust, smoke, pesticides and fertilizers build up from agricultural activity, and industrial smog blows in from the Bay Area. Many of our cities, especially Bakersfield and Fresno, are among the most polluted in the nation.

Seeing Half Dome is especially tricky. It lies at the upper end of Yosemite Valley about two thirds of the way to the Sierra Crest. Although it rises 4,000 feet above the valley floor, it only barely peeks above the other cliffs of the valley. And there are high ridges between the dome and valley making a line of sight impossible.

But...there is a V-shaped notch made by the Merced River canyon that allows Half Dome to be seen from a narrow sliver of land cutting across the towns of Denair and Turlock. I drive past a spot near Keyes Road east of Turlock every Wednesday on the way to class, and if the winds have cleared out the smog, and I've remembered my camera, I can capture the huge mass of rock digitally. You have to know where to look, and you have to use a pretty powerful zoom, but it is there, along with Cloud's Rest.

I cropped the center of the picture above to highlight Half Dome, but it is still a little faint, so here are some outlines below to make it clearer, I hope.

People have remarked that the pictures are fakes, and I can't say much to that other than I wouldn't know how. Others have remarked how out of proportion Half Dome looks. I realize while looking at the picture that Half Dome is essentially a 4,000 foot cliff. That's a third of the height of the entire range. It really is huge.

Enjoy. For my local readers, if you want to see this view, it is about a third of mile south of the intersection of Keyes Road and Hickman Road east of Turlock

Strangers in a Strange Land; or more like Strangers in their own land

Strangers in a Strange Land is an exploration of the geology of Death Valley National Park and the Mojave National Preserve, as it might be seen (and possibly even understood) by a new student of geology. My trip turns out to have been in two parts, a five day journey over the President's holiday weekend with 30 students, and a second trip (just completed) to the Mojave National Preserve (with the National Association of Geoscience Teachers). Mrs. Geotripper and I made use of a spare day with a quick swing through Death Valley, exploring some of the places we've never seen with students.

I've been known to complain about being upstaged while lecturing by furry or scaly animals on my field trips. Really, would someone go to a park like Yosemite just to see deer or chipmunks??? Then again, something like this happens....

We were headed up a rather rough dirt track into a lesser known part of the park called Hole in the Wall (which will have a separate post of its own later on). We were surprised to see a herd of Desert Bighorn Sheep (Ovis canadensis nelsoni), six ewes and three lambs, grazing in the canyon along the road. I've been coming to Death Valley for more than twenty years, and this was the first time I had seen any here. That is partly a function of my short visits, but is also a consequence of big changes in the population of the sheep in the park.

Twenty years ago, one rarely saw bighorn sheep, but almost always saw feral burros, descendants of animals let loose by miners a century ago. The burros competed for forage and water sources, so the sheep declined in population (they also declined because of diseases introduced by domestic sheep). The park service instituted an effort to remove something like 3,000 burros, leaving a population of around 100. The bighorns have rebounded nicely.

The sheep were cautious about our presence. They were grazing on both sides of the road we were following, and they moved away from us deliberately, but not in a panic. We drove slowly so as to not scare them. Eventually they moved up the hill a bit and waited until we left the area (having taken 30-40 photos of course). We went up the canyon for the next hour, and when we came back down, they were along the road again.

We stopped and decided to have lunch but stopped upstream of the herd, so as to bother them as little as possible. I saw one or two peeking around the corner down the canyon a few times.

Eventually we had to leave so we got in the car and drove down the canyon. They watched us from above the road, but by now were not retreating. They just waited and looked down on us. It was a transforming moment for me.

Bighorn sheep are an integral part of the desert landscape of the western United States. They appear in tens of thousands of petroglyphs, far more than other animals, and thus were an imprtant part of Native American culture. With the arrival of Europeans, both the Native Americans and the sheep became strangers in their own land. I was so glad to see that the bighorns were reclaiming at least a corner of their ancestral home.