Tales From the Semi-Super-Bloom Tour, Part 3: On the Road to Yosemite

Mrs. Geotripper and I didn't see the legendary "Super-Bloom" in Southern California. We didn't have the time or patience to deal with the crowds and trampling and helicopter landings in fields of flowers. We instead set out to find the evidence of spring in some less heralded and less crowded places that were perhaps not in a state of a once-in-a-decade superbloom, but showed some delightful color nonetheless. At the end of March it was the Mojave Desert and Death Valley National Park. Then a week ago we headed up to Yosemite Valley.

Yosemite Valley is just coming out of the throes of winter, so we weren't expecting any flowers there, and as such we were not disappointed. But our journey from the floor of the Great Valley and through the Merced River Valley provided us with an explosion of color. The prairies east of Merced and Planada were rich with Blue Dicks.

We climbed into the foothills and made a brief stop in Midpines where we saw these Baby Blue Eyes (above), and blooming Redbuds that aren't exactly really red.

Our road dropped into the canyon of the Merced River, and we followed the swollen river upstream. As we approached the village of El Portal, the flowers grew thick along the slopes. Golden Poppies were common, offset against the somber metamorphic rocks of the Shoofly Complex.

I've seen Golden Poppies growing in a wide variety of habitats throughout California, from high mountain slopes to deep forests to desert plains. No wonder they were declared our state flower.

We turned a corner and were greeted by slopes covered with purple lupines and Golden Poppies.

It's not a "super-bloom", it's merely a drought-free spring. But spring in the Merced River canyon is a colorful affair. It's a privilege to live close enough to see these beautiful slopes.

A Series of Fortunate Events: Fall in Yosemite National Park

 It was a privilege this last weekend to conduct a field studies exploration of Yosemite National Park and the surrounding region. It was a new class, but was similar to one we last taught back in 2008 when the Great Recession put a serious crimp in the scheduling of our field studies courses (we still did them, but there were fewer of them). Even better, I have another day trip scheduled on Saturday for a different course. Yosemite twice in a week!

I say it in a joking manner, telling students they have to "earn" the right to explore Yosemite. It's true though, in a way. There is a lot of geologic history in the rocks west of Yosemite National Park, and they help us to understand the origin of the rocks in the park. An example is the outcrop along Highway 140 between Merced and Mariposa. Just east of Dial's Rock Shop is an exposure of the Mariposa Slate.

The Mariposa Slate is a deposit that formed on the bottom of a deep sea off the coast of California in Jurassic time. The shoreline lay east of where it is today, and the Sierra Nevada was a different place: a series of active volcanoes led to a coastal forest. Dinosaurs, pterosaurs, and primitive mammals roamed the forests and floodplains. In the sea, large swimming reptiles including plesiosaurs and ichthyosaurs were found. The Mariposa is somewhat less altered than many other rocks of the metamorphic belt, and because of this, a few fossils have been found which enabled geologist to figure out the age of the rocks. This was an important step in unraveling the complex geologic history of the region.

The Mariposa is part of a large section of crust called the Foothills Terrane, a group of rocks that were added to the western part of North America during Triassic and Jurassic time along a subduction zone plate boundary. A great deal of compression caused the rocks to be tightly folded, as can be seen in the photo above (note a set of car keys just below the center of the shot). The slate has excellent rock cleavage (the tendency to split into very flat surfaces) so it finds use as chalkboards and billiard tables. There is a quarry on the top  of the hill above the outcrop (you can just make out some heavy machinery in the second picture above, on the left side).

The Mesozoic subduction zone that placed the Mariposa Slate against the edge of the continent was also instrumental in the placement of the vast granitic plutons that are exposed today in Yosemite National Park. The slate provides some insight into what came before the intrusive igneous rocks.

Our path was not the straightest route. Instead of following Highway 140 directly into Yosemite, we turned south at Mariposa and followed Highway 49 to the town of Oakhurst. We were having a look at the largest living things in existence, as well one of the greatest mineral collections in the state. More next time!

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.

Work to Begin on the Ferguson Slide on Yosemite Highway 140

The problem with a lot of beautiful national parks in mountain landscapes is that they lie in mountain landscapes. The rugged terrain is subject to landslides, and my favorite nearby park, Yosemite, is no exception. The park has four entrances, but only one can be considered an "all weather" access point, as it follows the Merced River, and does not have to surmount any snow-covered passes. Highway 140 may be the lower route, but it is not without its problems. The Merced Canyon downstream of Yosemite Valley is rugged and steep, some 2,000 feet deep in places. Instead of granitic rock, it carves through the metamorphic rocks of the Mother Lode, including the sometimes unstable slate, phyllite and chert of the Calaveras Complex.

There was a prehistoric slide near Savage's Trading Post. The so-called Ferguson Slide had caused problems in the past, and Caltrans had been looking to stabilize it, but in 2006 it overwhelmed the mitigation efforts and gave way, covering 600 feet of Highway 140 with hundreds of thousands of tons of metamorphic rock. The highway was totally blocked, and there were serious fears that the slide could completely block the river valley and flood the small village upstream.

Local communities, especially Mariposa, were devastated by the Ferguson Slide. Tourism makes up a huge portion of their economy, and with the highway closed, no one was coming through town. The first temporary fix, two quickly built bridges that detoured around the slide, were impassable to buses. Mariposa continued to suffer economic losses, so by 2008 the bridges were realigned. At present there are are delays of up to 15 minutes waiting for traffic to pass the one-way road.

I missed the story at first in the newspaper last week ("newspaper": a form of information transfer that predates the internet), but work has begun on a "permanent" fix on the section of Highway 140 beneath the slide. The first part will involve the removal of more than 100,000 cubic yards of slide debris, followed by the construction of a 750-foot "rock shed" that will channel future debris slides over and across the highway. I've seen snow sheds before on many alpine passes, but this will be only the second rock shed in the country according to Caltrans. The project will cost $133 million and will be completed in fall 2019. The work is not expected to block traffic, as the "temporary" detour will remain open.

I understand that the rock shed approach will be one of the least environmentally intrusive approaches to mitigating the slide (assuming it's done right), but I'm struck by the fact that this one road repair will be only slightly less expensive than the complete renovation of Yosemite's infrastructure following the devastating floods of 1997 ($182 million in 1997 dollars). And it's been nearly twenty years since those renovations, and Congress has never been one to keep up with the care of our national parks. It would be nice if we could take care of our parks as well as we care for the access to those parks.

In any case, this is a good time to be visiting Yosemite via Highway 140. Despite the drought years, the spacing of the few rainstorms we've had has left a lot of greenery along the river corridor. I haven't been up there yet to check, but I'll bet the poppies will be blooming soon, and in force. I'll have a full report about April 11.

Three Roads Diverged...but why? Because there's a huge landslide, that's why...

It didn't take Ron Schott long to reveal why three roads diverged in the wood, the subject of yesterday's post on Highway 41 heading into Yosemite National Park. The Ferguson Slide was a problem child for CalTrans and road management crews for many years. The orientation of the river and the dip of the metamorphic rocks on the high ridge conspired with the undercutting effect of roadbuilding to destabilize the slope above the highway (you can see some of the slide activity in this video). The slide permanently covered the highway, and the first temporary bridge did not allow larger vehicles to make the 90 degree turn. Bus tours are the life-blood of the local economy, so the current bridge crosses the river at an angle so longer vehicles can cross safely. I blogged about the slide last year, when I compared the Ferguson slide to a different kind of mass wasting event just inside the park boundaries.

The fix is still temporary, with only a single lane available, so delays are common while cars wait at both ends. A more permanent solution is the subject of extensive studies, which can be reviewed here.

We had to wait at the slide both coming and going home from Yosemite yesterday, so I was able to hop out and photograph a couple of the emerging springtime wildflowers. It was cold and dreary, so most flowers weren't doing much (it had actually snowed the previous day), but a few Indian Paintbrush flowers were visible, and the redbuds were spectacular all up and down the Merced River Canyon. I really want to head back up in the next week or so, and see the poppies and fiddlenecks mantling the high slopes.

But, you ask, how was Yosemite? Spectacular in a different way. Coming up in a future post!

Rockslide on Highway 140 Near Yosemite (Video)

Headed up to Yosemite Valley today to see some waterfalls and enjoy the holiday. Had a wonderful time, but had an extra surprise. Got to see a modest rockslide on Highway 140 on our way there, and managed to catch it on video! We were driving down Highway 140 near Midpines on our way down to the Merced River when the new rockslide caught my attention. A lot of rock had already fallen, and given that there was a bulldozer parked on the other side, it was clear that the main event had happened a day or two earlier, but I decided I wanted a picture so we stopped and I hopped out.
As I approached the slide, I could see a couple of large boulders still perched near the top of the roadcut that looked unstable, and I could hear small pebbles bouncing down the slope. When I got closer, I realized the pebbles and cobbles were dropping out from under the larger boulders. The rock was slowly giving way and I had a suspicion (and yes, a secret hope) that it might be about to collapse. I moved the camera setting to video, and only a minute later I got lucky. I was standing across the highway, and luckily no cars were passing at the moment. A couple of the broken chunks landed on the highway

The picture above is the only shot I got before the slide. The rocks on the lower part of the roadcut are probably greenstones, metamorphic volcanic rock, while the unstable material above is metamorphic slate. Both are part of the late Paleozoic Calaveras Complex or Sullivan Terrane. The material was deeply weathered (thus the red coloration), which contributed to the slope instability. Further instability was introduced by having a roadcut in the first place, which oversteepened the slope, and by the tremendous amount of precipitation we've had this year, around 150% of normal. There were numerous other examples of recent slope failures along the entire Highway from Mariposa to the entrance of Yosemite National Park.


Sure, it wasn't the biggest slide in the world, but it was very loud, and it was very cool to be standing in front of it when it happened. You can hear me starting to say "I'm O.K." at the end of the recording, mainly because my wife was down the road a bit and heard the rocks drop, but couldn't see me.