Sunday, July 15, 2018

Conjunction of Inanna and Theia's Child Tonight

There was quite the spectacle in the heavens tonight, the conjunction of Inanna and Theia's child. Obviously some explanation is needed here since most people refer to these heavenly bodies as the planet Venus and the Moon. Inanna was the Sumerian name for the brightest planet, and they may have been the first people to surmise that the Morning Star and the Evening Star were the same object. The goddess they worshipped morphed into Ishtar and influenced the idea of Aphrodite. Venus was the Roman version of the deity.
Theia refers to the Mars-sized planetoid that collided with Earth early in her history that resulted in the formation of the Moon. The event probably took place about 4.51 billion years ago, very shortly after the formation of Earth itself. The hypothesis explains many of the odd chemical characteristics shared by the Moon and the Earth.
This picture was taken 45 minutes earlier than the first. Note the change in the position of he Moon (it moves much faster against the background.

In any case it was a beautiful sight tonight in the western sky shortly after sunset. I took pictures over a period of about 45 minutes and the relative position of the two celestial bodies was noticeably different.

Saturday, July 7, 2018

Home From Back of Beyond: Images of a Harsh Country, Part Three

This first photo may recall the disasters unfolding in the American West and Hawai'i with out-of-control wildfires and volcanic eruptions, but in this case it is no disaster. It is was the sunset on the tenth day of our recent exploration of the Colorado Plateau. We had finished our explorations of Arches and Canyonlands National Park and were headed west, towards home. It's funny, the emotions that can arise on a long journey. It felt like we were nearing the end of the trip yet we still had five days and four nights to go, and there were still four national parks on the itinerary. I've put together two previous posts of my favorite shots from the trip, and this is the third and final chapter.
We had been out for a long time, so we gave the students half a day of free time in Moab, Utah to do laundry, shower, and peruse the rock shops. But first we had one other major archaeological stop to make. The sandstone walls of the Colorado River gorge downstream of Moab contain some fascinating petroglyphs. They are cleverly hidden behind a big highway sign that says "Indian Writings".
Having signs pointing to fragile petroglyphs along a busy highway might not seem to be a good preservation strategy, but in this the highway construction itself provided the protection. There was very little space along the river for road construction, so the crews removed many tons of fallen debris to make room, the same debris the original artists stood on to chip out their art. Many of the petroglyphs are now inaccessible, fifteen or twenty feet above the roadway. One of the most unique is the bear, surrounded by hunters with bows and arrows (I think the artist was bragging).
In the afternoon we headed west and south across the barren lands around Green River. The small village is the final settlement for a hundred miles west along Interstate 70. The only settlement to the south is Hanksville, around fifty miles away. We were in one of the most isolated regions of the lower 48 states. Our destination for the night was Goblin Valley State Park on the San Rafael Swell. The sunset was glorious (the first picture of today's post was also taken there).
In Jurassic time an ocean embayment extended south from Canada into the Colorado Plateau region. Called the Sundance Sea, it left behind all manner of tidal flats, delta deposits, and coastal dunes. The Entrada Sandstone displays many of these environments, and erosion has carved the rock into a variety of fascinating shapes. For one, most of the arches of Arches National Park occur in the Entrada. At Goblin Valley, the rocks were more thinly-bedded and produced small mushroom-shaped spires that gave the valley its name. If you are a fan of sci-fi flicks, you may recognize Goblin Valley as the setting for some scenes from Galaxy Quest (the one with the little purple aliens and the rock monster).
Looking south from Goblin Valley we could see the high peaks of the Henry Mountains, often described as the last mountain range in the United States to be discovered and explored (in the 1870s). Like the La Sal Mountains described in the last post, they are laccoliths, mushroom-shaped intrusions of magma. It was at the Henry Mountains that the term laccolith was first proposed by Grove Karl Gilbert, a pioneering American geologist.
Stars. Night after night of the most starlit skies I can remember. We were in the darkest corner of the continent, and our nights for the entire trip had been free of moonlight, but the following day the thinnest crescent moon I could remember ever seeing was setting in the west. I noticed later that this first appearance of the moon on June 14 was the ending of the month of Ramadan.
Our destination the following morning was Bryce Canyon National Park. The Colorado Plateau is a remarkable region because for close to a billion years it had been remarkably stable, remaining at or close to sea level throughout Paleozoic and Mesozoic time. But in the Cenozoic this began to change as the land rose above sea level for the last time. During the early Cenozoic Era (60-40 million years ago) the region around Bryce Canyon was a huge freshwater lake. The resulting pink siltstone an limestone layer is called the Claron Formation.
The rocks of the Claron Formation are cut by vertical fractures called joints, and these fractures allow water and ice to widen the cracks and forming the spires of Bryce Canyon. The rock towers are called hoodoos. Sometimes arches and natural bridges will form during this process (natural bridges cover a watercourse while arches do not). Does anyone want to guess what kind of opening this is in the picture below? (Hint: It's named Natural Bridge)
Bryce Canyon is an exceedingly popular national park. Besides the spectacular scenery, it lies in close proximity to Zion and Grand Canyon National Parks and thus makes a "grand triangle" of a tour so beloved by bus companies and tourists on a time budget. The popularity combined with the rush that most people are in to get to the most possible localities means that certain parts of the park are more impacted than others. The free trams go to the most crowded parking lots, and the entire south end of the park tends to be far less crowded and hectic (at least in my experience). If you ever visit, make every effort to go beyond Inspiration Point and see Rainbow Point and the many other pullouts. It will take you no longer to see them than it will to wait for a parking spot to open up at the more popular viewpoints.

By the time we left Bryce that afternoon we were making serious mileage towards home. We crossed the deserts of western Utah and arrived at one of my favorite national parks of all: Great Basin. The park is not a basin, it's a mountain range, the Snake Range. It was established in 1986, although a small portion, Lehman Caves, was made a national monument in 1922. The political journey leading to the establishment of the park was different than most. As I came to understand it (and please, provide some insight in the comments if I have this wrong), there was a desire to have a national park representing the best of the Basin and Range geologic province, but promoters were split between three possible locales! There was the Toiyabe Range in central Nevada, the Ruby Range/East Humboldt Range in the northwest part of the state, and the Snake Range, which got the eventual nod. Purists supported the Toiyabe Range because it best exemplified the unique ecosystems of the Great Basin whereas the other two showed more affinities for Rocky Mountain flora. It was an interesting problem because the Ruby Mountains and Snake Range offered more "normal" mountain scenery along with glacial lakes. They really are a bit more like the Rockies. I suspect that the Snake Range got the nod because it already had the infrastructure for a national park (an extant visitor center, for instance), it had Lehman Cave as a centerpiece, but it also had Nevada's only glacier, and a forest of Bristlecone Pines, the oldest living organisms on the planet.

The park also protects Wheeler Peak (13,063 feet), which is the highest peak entirely within the boundaries of the state of Nevada (the actual high point, Boundary Peak, is a spur on the ridge of a higher peak in California, and it is only about 50 feet higher than Wheeler). There is a spectacular ridge-hugging paved road that reaches the main trailheads at over 10,000 feet.
Great Basin is one of my favorites because it still retains the character of what most national parks once were: havens of serenity and wilderness. The park is generally uncrowded (except for the lines at the visitor center for cavern tour tickets), and mostly undeveloped. There are roads and campgrounds, for instance, but many of the roads are unpaved, and the campgrounds are old style: vault toilets, and no hook-ups. The last time I checked, the campfire programs were actually done around campfires, without screens and PowerPoint presentations. I hesitate to even tell you about this because you might want to go and see it, and it will get crowded like all the rest. Just kidding, go see it. It's beautiful, and the caverns are wonderful too.
The next day was a long drive across Nevada, and we had one more night, staying at Berlin-Ichthyosaur State Park. It's a fascinating place and I would describe it in detail, but I took few pictures, and this post is all about my favorite shots from the trip (you can read some details in this post from a previous trip). The next morning we were homebound and quickly crossed the western desert hills of Nevada. We crossed Anchorite Pass and rolled into our home state of California  In a matter of minutes Mono Lake came into view. We took a break at the Interagency Visitor Center at Lee Vining.
Mono Lake is a singular ecosystem in California, like no other place in the state. It occupies a large tectonic basin, meaning it has no (current) natural outlet. Lots of water flows into the lake via streams from the adjacent Sierra Nevada, but the only way water can leave is by way of evaporation. Because of this, the salt content of the lake is three times that of seawater. Few organisms can survive such conditions, so the ecosystem is pretty straightforward: some algae, trillions of brine shrimp, trillions of brine flies, and millions of migratory and resident bird species. Mono Lake is one of the most important stops on the Pacific migratory flyway.

Unfortunately humans always find a way to muck things up, and Los Angeles worked really hard to mess up this system. It involved building a 200 mile-long aqueduct and an eleven mile-long tunnel under a series of volcanoes to siphon off water from the tributaries that drain into Mono Lake. When the city closed off the streams in 1941 Mono Lake began drying up and lost 45 feet of elevation. The salinity drastically increased, threatening to kill off the shrimp. Lawsuits dragged on for years, but now an agreement is in place to raise the lake to a sustainable level. If only the California drought would cooperate...

The day we arrived the lake was (for me) an unusual shade of turquoise. The clouds were a sight as well. There had been not a great many clouds during our trip. The lack of rain was nice, but the entire route of our trip has been in the grip of an exceptionally severe drought. We wouldn't have minded a drencher if it could have helped.

Our final national park of the trip was in some ways the most familiar, but we didn't see it from a normal angle. Something like 90% of the people who visit Yosemite National Park go to the iconic valley, but the valley makes up only 7 square miles of a 1,000 square mile park. We entered the park at Tioga Pass (9,945 feet) and drove through the alpine meadows of the upper Tuolumne River. After more than 3,000 miles of barren desert environments, the greenery was stunning. We made a final lecture stop at Olmsted Point, which provided a unique view of Half Dome, from upstream.

But that was it. Once everyone realized that we had crossed the headwaters of the river that flows through our community, there was no slowing down. Homesickness is a powerful emotion and it was almost as if our vans took on a life of their own as we rolled down the western slope of the Sierra Nevada to the end of our journey. Like crazed tourists, we had visited 10 national parks, 9 national monuments and recreation areas, and maybe a dozen state parks. We had traversed a geological history encompassing 1.7 billion years of geological events and thousands of years of human history. All it took was 15 days, 3,700 miles, and a great group of students and volunteers!

Come join us some time in the future. We're headed to the Cascades this fall with a five day trip to Mt. Shasta, Lava Beds National Monument, Lassen Volcanic National Park, and McArthur-Burney Falls State Park. Contact me for details...

River Otter on the Tuolumne

I am quite lucky to have the Tuolumne River in my backyard. The river rises in the highest regions of Yosemite National Park, flows through incredible and largely unknown gorges that rival the Grand Canyon in depth. Water is trapped in a series of reservoirs including Hetch Hetchy and Don Pedro, and at that point the river could have been cut off the way the San Joaquin River was destroyed. But water agreements have kept a minimum flow, so the river flows onto the floor of the Great Valley and maintains a continuous riparian habitat all the way to the Sacramento Delta. The river bed has been severely altered, first by the gold miners, and later by quarry operators and farmers. But portions are in the process of healing, and in places the stream is starting to resemble its earlier incarnation as a wild river.

I saw River Otters (Lontra canadensis) for the first time just two or three years ago, and I'll see them two or three times a year when I stroll along the river trail. This morning the water level was low and river transparent, so I saw what I thought was an immense fish maybe three feet long deep in the water. I turned on the camera to get video and hit the wrong button, but then the "fish" surfaced and I realized I was watching an Otter. I got the video going correctly and got some of the best "footage" so far.

River Otters are making a comeback in the rivers and streams of the San Joaquin and Sacramento Rivers and across the Bay Area. I'm so glad some of them have made it here to my little corner of the river! For more information on otter sightings and ecology, check out the River Otter Ecology Project.

Thursday, July 5, 2018

Home from Back of Beyond: Images of a Harsh Country, Part Two

The photo above encompasses so much of what captivates me about the southwestern United States. A trail formed from a natural weakness in the rock providing access to an otherwise inaccessible cliff to who knows where? To be fair, hundreds of thousands of people know where the trail leads, but I like the mystery of the image. The thing is, many people DO follow this trail every year, but they may not appreciate the fact that the last time this surface was exposed to the atmosphere, it was 200 million years ago, and on the slip face of a coastal dune. Some of the irregularities highlighted by the shadows in the picture could literally be the preserved footsteps of dinosaurs, other reptiles, or amphibians.

I am slowly working on a short series of posts with my favorite images from our recently completed exploration of the Colorado Plateau and surrounding provinces. I took 1,400 photographs, so it's a bit difficult to choose between them! As we pick up the narrative, we are eight days into a fifteen day trip. As seen in an earlier post, we'd already been to the Mojave National Preserve, Zion National Park, Grand Canyon National Park, Bear's Ears National Monument, and Mesa Verde National Park. As we left Mesa Verde, we needed to find a way over the San Juan Mountains, a major range within the Rocky Mountain chain.
Because of a major wildfire in the drainage of the Animas River above Durango, we had to find another route over the mountains, so we headed instead to Lizard Head Pass (10,222 feet/3,116 meters), which divides the drainage of the Dolores and San Miguel Rivers. There was a beautiful profile of the high peaks from the summit. The brightly colored rocks above the tree line are volcanic, part of the rhyolite caldera eruptions that were taking place around 35-30 million years ago. Mineralization related to the volcanic activity resulted the emplacement of gold and silver deposits. The old mining towns like Ouray and Telluride are picturesque, but the pollution relating to the mining is a sad heritage.
Near the town of Ouray, one of the old mining camps, there is a difficult-to-see waterfall called Box Canyon Falls. The 200 foot high falls are practically hidden in a deep slot canyon, but the slopes above reveal a spectacular angular unconformity. The underlying vertical layers are more than a billion years old, but erosion planed off the rocks and in Devonian time almost 400 million years ago new sediments were draped over the older rocks. The uplift of the San Juan Mountains caused further erosion, exposing the unconformity that represents almost a billion years of missing history.
Black Canyon of the Gunnison is possibly the most bizarre canyon on the continent. It is a nearly vertical gorge that cuts through what is essentially the top of a mountain instead of having been carved through softer rocks that are exposed nearby. The Gunnison River was forced into the present channel by a series of lava flows that diverted the river from a "normal" course. Around 2-3 million years ago the landscape was uplifted, and the trapped river cut down through all the rock in its path, including the extremely hard gneiss and granite that make up the canyon walls in the park. It's not the deepest canyon in the country, but no other canyon combines the depth and steepness of Black Canyon. It is more than 2,000 feet deep in places, and in one place it is only 1,100 feet wide.
The Painted Wall (above) in Black Canyon is the highest sheer cliff in Colorado at 2,250 feet. The rocks exposed in the face of the cliff include 1.7 billion year old gneiss and schist with numerous intrusions and dikes of lighter colored granitic rock, including extremely coarse-grained pegmatite.
Late in the day we headed down one of the most spectacular roads in North America, Highway 128, which follows the Colorado River from near Interstate 70 to the outskirts of Moab, Utah. While mostly confined to a deep and narrow gorge of sandstone cliffs along the river, there is a moment when the canyon opens up and there is an awe-inspiring view of the Fisher Towers and the La Sal Mountains.

The La Sal Mountains are an anomaly in the generally horizonal landscapes of the Colorado Plateau. Between 28 and 25 million years ago, plumes of magma worked their way almost to the surface, intruding laterally between the sedimentary layers, and causing them to swell upwards like a series of blisters in the crust. The intrusions are called laccoliths. Exposed now by erosion, the igneous rocks reach elevations of almost 13,000 feet.
We arrived at our campsite in Arches National Park as the sun approached the western horizon. I don't think there is a more spectacular place in the country to roll out a sleeping bag. The view from the group camp extends for miles in every direction. There is also a beautiful arch, Skyline, visible from camp (below). The arch more than doubled in size in 1940 when a huge chunk of rock fell from the opening.

The landscapes in and around Arches and Canyonlands National Parks are almost beyond description. We spent two days in the area, and one of our stops was a rock art panel that is so delicate and fragile that I can't believe that it still exists 30 years after I first discovered it. Why? It's easily seen from the paved road leading into Canyonlands. But without signs and arrows pointing the way, people miss it. The first of the images are pictographs (below), those examples of rock art that were painted onto the sandstone. The ghostly figures and small hummingbirds are almost nightmarish in their imagery.
The other images are petroglyphs, the ones carved directly from the rocks. They depict some stylized bighorn sheep and other creatures. The panel has been somewhat damaged, possibly by natural erosion, but vandals have also done their evil work here.
Canyonlands National Park has many incredible vistas, but my favorite is the one that is framed by Mesa Arch (below). The arch is relatively small, but it frames the La Sal Mountains and pillars and cliffs of the Colorado River section of the park (the Green River forms meets the Colorado inside the park). Mesa is a popular short trail, and crowds are especially thick in the early morning when the sunrise can be photographed through the opening. You've no doubt seen an example on just about any nature-based calendar!

Pictures of Canyonlands are often mistaken for the Grand Canyon, but this section of the river includes only late Paleozoic rocks and thousands of feet of Mesozoic layers that are not seen at Grand Canyon. It is not as deep, but it is deeply colorful. It's hotter country in the summer, and there aren't many sources of water. Travel away from paved roads is more challenging than your "average" national park.
After we explored the Island in the Sky District of Canyonlands and Dead Horse Point State Park, we headed back to Arches for one of the greatest excursions on our entire trip, the hike to Delicate Arch for the sunset. The trail (a picture of which started this post) climbs 1.5 miles to an iconic overlook of the famous arch. I would love to say that the hike is an awesome desert wilderness trek where one can discover one's self in the isolation and serenity, but as author Edward Abbey feared in his 1968 book Desert Solitaire, the trail (and much of the rest of the park) has been taken over by industrial tourism. There is a large paved parking lot, and hundreds of people make the trek every evening.

Frame Arch view of Delicate Arch
The crowd at the top was rowdy, in large part because there are always selfish individuals and groups who insist on standing within the arch for selfies and group photos, spoiling the view for everyone else. I didn't have the heart to listen to the ruckus (I most certainly would have contributed, shouting at the jerks in the arch), so I headed instead to my favorite little arch in the park, Frame Arch. Frame is a small arch just above the trail only a few dozen yards from the Delicate Arch viewpoint. Most people pass it by in their race to get to more famous arch around the corner. What most of them don't realize is that Frame Arch has a great view of Delicate Arch, but also of the La Sal Mountains and Salt Wash. And I had the arch to myself for quite awhile even as hundreds of people were gathered just around the corner.
The La Sal Mountains and Salt Wash through Frame Arch
I had to think of my students though. There were a dozen of them who had hiked ahead of me, and they had to be worrying that their old overweight professor was passed out somewhere down the trail dying while they were enjoying the view. So I climbed down from the arch and back onto the trail and walked the last few yards to the overlook. I patiently waited while the jerks stood for their pictures in Delicate Arch and finally got a picture sans people as the sun settled into the horizon.

Our trip wasn't over. We had five more days and two more states to traverse. More favorite pictures soon!

Tuesday, July 3, 2018

The Deepest Pass in North America, and Finally Taking THE Aerial Tramway

Last weekend I was having lunch in Palm Springs. That might sound, I dunno, elitist or something, but we were actually in Beaumont, and we hadn't seen the city of golf courses and the idle rich in decades so there we were. Driving down the main drag, we saw the Palm Springs Art Museum, and said "why not?" and paid a visit. Several hours later I had seen most of it and decided to walk around the grounds and discovered a trailhead! I read the sign, and found it was the Skyline Trail, which climbs around 8,000 feet up the flank of San Jacinto Peak (10,804 feet) in twelve miles. It's said to be one of the most difficult and dangerous in the country, especially in the summer when temperatures can soar to 115 degrees. There's no water or shade for most of the climb.

Well, I had my hat. I had half a bottle of water. It was 4 PM and only 103 degrees and no one knew where I was. So off I went up the trail. At this point you may be thinking that I am about to describe a real disaster of bad judgment and pointless rescue, but no, I'm not quite that stupid (Mrs. Geotripper may have an alternate opinion on this). I went up maybe 200 yards, high enough to get some pictures of the city over the tops of the palm trees on the adjacent golf course, and headed back down to the museum to cool off.

But just the thought of the trail had reawakened a great many memories of my days as a teen in Southern California. I was practically indestructible in those days and was recognized as the fastest long-distance hiker in my high school. I climbed Mt. Baldy via the "old" trail that climbed 6,000 feet to the top, and summited at least fifty other peaks. But I never walked to the top of San Jacinto starting from the desert floor. At the time, I hadn't heard of the Skyline Trail, but had learned of a climber's route up Snow Canyon, but never found the time. All I knew was that San Jacinto Peak was a very high mountain that rose from desert plains only a short distance above sea level. The escarpment of San Jacinto is one of the highest and steepest in North America.

There is a mountain ridge across from San Jacinto that is even higher. San Gorgonio Peak is the highest mountain in Southern California at 11,499 feet. The pass between the two mountain ranges tops out at just 2,600 feet, meaning that San Gorgonio Pass is probably the deepest pass in North America, at nearly 9,000 feet. It's nearly twice as deep as the Grand Canyon, and deeper than the deepest canyons on the continent, Hells Canyon of the Snake River, and Kings Canyon in the Sierra Nevada.
Mrs. Geotripper had some sympathy for my vague feelings of disquiet about not finishing the hike and offered that I should just take the Palm Springs Aerial Tramway up to Long Valley where the trail ends. I could accomplish the same thing as the killer hike in about 12 minutes for only $25. I struggled for a moment with my lifelong philosophy that incredible views have to be earned by sweat, but then said yes. We headed up Chino Canyon to the base of the tramway.

For those of you who are not familiar with the tramway, it is quite an engineering feat. The tram begins at 2,643 feet in the Lower Sonoran life zone and climbs to 8,516 feet in the Canadian or Hudsonian zone. It is two and a half miles long and is supported by five towers, the tallest of which is more than 200 feet. It was constructed in 1963 and with no roads or trails in the rugged terrain, much of the construction was accomplished with helicopters.
It was my first time on the tram, but not my first time at the Mountain Station at the top. Many years ago I had walked to the station from the trailhead in Idylwild on the other side of the mountain. It was one of those classic hikes where the ten or so of us teens went wandering off from camp without really preparing for a long hike only to find as the sun was setting that we had a single flashlight for the whole group for the three mile hike back in the dark. The minister who was our group leader was kind of frantic as the night wore on with a large part of his group missing. It was a fine adventure all those years ago.

We were lucky last weekend, because the atmosphere was reasonably clear and the view was spectacular. Joshua Tree National Park stretched across the valley beyond Palm Springs. We could see the deep canyon of the Whitewater River, the main canyon draining the east side of San Gorgonio, now part of Sand to Snow National Monument. At our feet we could see some of the 4,000 turbines of the San Gorgonio Wind Farm in the pass (below). The pass is one of the windiest spots in all of California, owing to the height of the surrounding mountains and relative narrowness of the pass.

There was also a panorama above, as we were standing along the edge of a high-altitude plateau of the San Jacinto massif. The relatively gentle slopes and valleys of the highland are a relict surface of the landscape that existed before the mountains rose thousands of feet along the bounding fault lines.
All of this leads to a question: what geological processes combined to form this extraordinary landscape? Actually, it has to be two sets of questions, because one needs an explanation for the landscape, but also an explanation for the rocks that underlie the landscape.

First, some regional context. The San Jacinto Mountains are part of the Sierra Nevada, sort of. They are officially described as the northern end of the Peninsular Ranges, which extend all the way down the Baja Peninsula for another 700 miles south of the border. But the rocks themselves originated along the huge Mesozoic subduction zone that extended from Mexico to Canada. There was a continuous mass of granite that included the Sierra Nevada, the Salinian Block, and the Peninsular Ranges batholith. Later on the Salinian Block was carried northwest along the San Andreas fault, and the Peninsular Ranges more or less ended up in the location from where the Salinian Block had been removed.

The rocks themselves are what most normal people would call "granite", light-colored (feldspar and quartz-bearing) plutonic rocks overall with black specks of biotite mica or hornblende. Geologists will concede to calling the rocks "granitic", but look at the proportions of feldspar varieties and quartz to come up with some more imposing names like quartz diorite, quartz monzonite, and hornblende diorite. These rocks formed in the subduction zone where oceanic crust and continental sediments were pushed so deep into the mantle that some of the material melted and rose through the crust as magma plutons. These masses rose until they reached some form of buoyancy and cooled slowly over tens of thousands or hundreds of thousands of years, forming the coarser-grained granitic rock. Later on erosion removed the miles of overlying crust to expose the sparkling plutonic rocks.
As the granite is released from the great pressure of deep burial, the rocks expand and crack, forming prominent vertical joints. The joints are wedged apart in the winter by ice, with some rocks falling away and others remaining in place as spires and towers on the steep slopes.

During the tram ride up the mountain, the rider is treated with some awesome views of the granitic rocks. In many places the granite has been pierced by light-colored dikes. These were silica-rich masses of the last bit of molten material that filled cracks in the final stages of cooling. Some of the dikes are pegmatites, made up of unusually large (inches across, sometimes a foot or more) crystals of quartz, feldspar, and sometimes gemstones like tourmaline, garnet, topaz, or beryl. The gemstones are still mined in other parts of the Peninsular Ranges. I really wanted to call for the tram to stop and let me down a rope to check out the exposures!

The next picture below shows an especially prominent dike that has resisted erosion and now stands out in relief. It actually looks like some of the "cartoons" I use in lab to teach sequence of geologic events. Which came last, the grey rock, the horizontal white dikes, or the vertical dike that stands out in relief?

The final part of the story is in some ways the most difficult. How did the Peninsular Ranges become mountains, and why is there such a deep pass between them? I don't know that I have a great answer to that question, but one can assume that fault lies with the faults. Several major faults pass through the pass, including the most familiar of all, the San Andreas. But the San Andreas is a strike-slip, or lateral moving fault, not one that leads to vertical uplift. There are complications in the path of the fault though that can explain why there are mountains here.

If the trace of a strike-slip fault is absolutely straight, over time the fault won't cause much in the way of uplift as it moves. The trace of the San Andreas through the Carrizo Plains farther to the northwest demonstrates this (the fault has only produced low hills there). But if there are bends or turns in the path of the fault, local areas of extension or compression can develop that will cause vertical uplift (or basin subsidence). The Peninsular Ranges form the western margin of the Coachella Valley, which is the northern extension of the fault basin (and divergent boundary) of the Gulf of California. The continent here is ripping apart, and the valley has sunk thousands of feet. In at least one way, the San Jacinto massif can be thought of as forming from the sinking of the adjacent valley rather than being "pushed" upwards, although there may be some element of that going on as well (thrust faults are present on the north side of San Gorgonio Pass).

The San Andreas fault was visible from the tramway. The zoomed image above shows Highway 62 where it passes through the Little San Bernardino Mountains on the way to Morongo Valley. The fault passes along the base of the mountain range.
We had a dinner appointment elsewhere, so the time to descend from the mountain top came much too soon, but down we went, dropping 6,000 feet in 10 minutes. My ears popped a couple of times. It was an awesome experience, but I still had the disquieting feeling that these incredibly steep and rugged cliffs were not a place for humans. They are more the domain of the hawks and condors.

A small postscript: "That's AMAZING!" I miss Huell Howser and his unique explorations of California. Here is his 1997 episode that included the Palm Springs Aerial Tramway as well as the 13 mile long tunnel underneath the San Jacinto Mountains that was constructed to deliver Colorado River water to Southern California:

Friday, June 29, 2018

Geotripper Presentation on Earthquakes at Hemet Library, Saturday 6/30 at 2:00 PM

IArt by A. June

If you happen to be in the vicinity of Hemet, CA tomorrow, you might consider stopping by the Hemet Library at about 2:00 PM. I'll be giving a presentation on "What you already know about earthquakes...are you right??". We'll be talking about some of the myths and misunderstandings about earthquakes, and maybe shed a bit of light on the earthquake hazards of Southern California.