The Right Place at the Wrong Time: A January Sunset at Olmsted Point

Yesterday I saw sights I never thought I would see: Tioga Pass in mid-January, short of snow but full of incredible beauty. There was so much to see in few hours I had, not the least of which was the sunset. We drove west from the summit of Tioga Pass back down through Tuolumne Meadows and Tenaya Lake.

As we saw in yesterday's post, Tenaya Lake is covered with a thick sheet of ice. As the sun approached the horizon, the colors on the peaks above intensified. Being able to walk out onto the lake allows for unique photo angles that are more difficult during the summer.

We drove to Olmsted Point to watch the evening drama play itself out. I climbed up on the smooth granite slopes above the parking lot and snapped pictures in several directions. For those who have only seen Yosemite from the valley floor, Olmsted is an incredible sight. To the south, Half Dome rises above the ridge. Yosemite Valley is hidden deep in the shadows below the ridge.

The dominant mountain to the south is Clouds Rest, the highest peak visible from the floor of Yosemite Valley. It is a massive piece of granite that has been scoured by repeated snow avalanches, forming the unique chutes visible from Olmsted.

To the north is one of the most famous views of Yosemite, Tenaya Lake with the backdrop of Mt. Conness on the Sierra Crest. The glacial geology is a bit unusual here. Tenaya Lake's canyon barely has any kind of creek, much less a river. It doesn't seem like a big enough drainage to have had glaciers, but glaciers it had. It turns out that nearby Tuolumne Meadows was covered by a massive ice cap more than 2,000 feet thick. Most of the ice flowed down the canyon of the Tuolumne River, but some of the ice flowed over the low divide into the drainage of Tenaya Creek which flows into Yosemite Valley. The consequence is that Tenaya Creek had a much larger glacier than it otherwise would have had. It was Tuolumne River ice that carved a major portion of Yosemite Valley on the Merced River.

During the summer, the sun sets more to the northwest. Today, just a few weeks after the winter solstice, the sun was setting far to the southwest, and whatever light and shadows are present at that time are quite different from what one would see in the summer. I'll just have to come back up next summer and see how different things are at the opposite solstice (any excuse works for me!).

 The color deepened, and I took another set of images as the sun settled into the horizon...

It was a real privilege to be in the High Sierra in the midst of January. With the lack of snow, I worry about our drought and the fires that are sure to come this summer, but today it was strange and wonderful.

A Convergence of Wonders, Day 16: Our Home Mountains, Giant Swimming Reptiles, and a Bunny

After 15 days and 4,200 miles, we woke up to the last day of our Convergence of Wonders, the geological tour of the Pacific Northwest and Northern Rocky Mountains. It was June 30th. We had traveled through the Cascades and the Coast Ranges, the present-day manifestation of convergence along the Cascadia Subduction Zone. We had traveled across the Columbia Plateau and the Channeled Scablands, and looked at evidence of past convergence in Montana's Glacier National Park, and Sun Canyon. We explored the inner parts of the earth's crust along the Beartooth Highway, and saw the evidence for a gigantic mantle plume (hot spot) at Yellowstone National Park. We saw the vast heavings of fault lines in the crust at Grand Teton National Park. And now, after a series of adventures in Utah and Nevada, we were finally headed home.

In the most technical sense, we could have started driving and made it home for a late lunch. But we couldn't pass up several of the most spectacular geological sights of our trip. We were almost home, but we could still be distracted by geological sights!

When we arrived at Berlin-Ichthyosaur State Park very late the previous night, not a few of our students were just a bit spooked by finding we were spending the night in a ghost town. The menacing looking ruins of the dark night were a little less nerve-wracking in the morning sun, so we packed and headed up to the quarry for a tour. Berlin-Ichthyosaur is a two-fer park: it preserves a late 1800's gold mining town, and a 200 million year old paleontology dig.

The ichthyosaurs were the dolphins/whales of the dinosaur era, the Mesozoic, aside for being in the wrong biological class. Whales and dolphins are mammals, of course, and the mammals were a rather minor part of the Mesozoic ecosystem, and as far as I know, none of them were adapted to marine conditions. Ichthyosaurs were air-breathing reptiles that were wonderfully adapted to life in the sea. They had the four limbs of their terrestrial ancestors, but their body shape was streamlined for fast swimming in the oceans. There were many species, ranging in length from a meter (3 feet) to 20 meters or more (65 feet). They had huge eyes, exceeding the size of pie plate in some of the larger species. That's a full-scale model of a Shonisaurus popularis in the picture above (the fat one is Geotripper himself, providing scale), the species found at Berlin-Ichthyosaur.

The bones of the ichthyosaurs were first noted by the miners, who used the massive vertebrae as doorstops and dinner plates. The site was excavated by paleontologists in the 1950s and 60s, who discovered more than three dozen more or less complete specimens. Nine or ten specimens were left in place for public viewing, and a structure was built over the site.

The bones don't differ overmuch in color from the surrounding rock, but the shapes are fairly obvious. The parallel bones above are ribs. Below are a number of vertebrae.

The skulls were the most delicate part of the skeleton, and were often crushed during preservation. Some portions of a skull are present in the photo below. Few teeth were found at the site.

One of the mysteries is why so many of the ichthyosaurs ended up dead in this one place. Numerous ideas have been suggested, including strandings, volcanic eruptions, spawning behaviour and others, but the favored explanation of the moment based on available evidence is that they died from mass poisoning, much as marine animals are killed today by red tides (toxic microorganisms). For more information on the topic, check out vignette 14 in Geology Underfoot in Central Nevada, by Orndorff, Wieder and Filkorn.

After our excellent tour by ranger Robin Riggs, we hit the road, and after a few hours we passed a welcome sign, the one that said we were back in California. Our beautiful home mountains, the Sierra Nevada, filled the horizon.

 Highway 167 is a very straight road in this part of the country!

Lest the students get lazy, we still had a few classes to go! We stopped in at Mono Lake County Park to sit in the grass under the Cottonwood trees. Mono Lake is an interior drainage lake; water flows in, but doesn't flow out. During the ice ages, glacial meltwater filled the basin, forming a lake 600 feet deeper that overflowed into adjacent basins, with water ultimately reaching Death Valley. In recent times the lake was 45 feet deeper than it is today, but in 1940, Los Angeles started diverting water from the incoming streams, and the lake started drying up.

 The spot we were walking on (below) was underwater half a century ago...

The lake is a critical stop for millions of migratory birds, as it has plentiful food in the form of fairy shrimp and brine flies. The birds need the nourishment to allow them to complete their long journeys. The conflict of human use and ecosystem preservation has dominated the politics of the region for decades. Recent agreements may stabilize the situation...maybe.

The mountains on the skyline are the Mono Craters, a series of rhyolite plug domes that have all erupted within the last 35,000 years or so. The last eruptions were only a few centuries ago. That makes this 9,000 foot ridge the youngest mountain range in the country.

Freshwater springs in the lake caused the formation of tufa towers, masses of calcium carbonate that stand like frozen sentries in the water.

After a quick lunch at the Whoa Nellie Deli, we headed over Tioga Pass and passed through Tuolumne Meadows in Yosemite National Park. By now, even the instructors wanted to go home, despite the incredible scenery. We will go see this stuff on a day trip later! Meanwhile we stopped for a wrap-up lecture and group photo at Olmsted Point. Half Dome loomed in the distance...

I snapped a quick picture of Mt. Conness and Tenaya Lake, and we got in the vans for the final hundred mile drive to Modesto.

We got in about 6 o'clock, and there were many happy shouts of reunions with loved ones. There was also a huge mess, but most of the students were cool enough to stay and help clean up. I love these folks! We were home. Mrs. Geotripper and I headed to the house said hi to our animals and managed to hang around the house for ten days before we got restless and hit the road again.

 As promised, here is the bunny. Mrs. Geotripper caught it in the early morning at Berlin-Ichthyosaur.

 It didn't fully cooperate in the careful posing category...

And that is the end of our Convergence of Wonders! I hope you enjoyed traveling with us!

Yosemite as an Open Air Classroom: Olmsted Point

At the height of the ice ages in the high Sierra Nevada, an ice cap 2,000 feet deep covered the Tuolumne Meadows region. A massive 40-mile long glacier flowed down the Tuolumne River gorge, the largest in the Sierra, but tongues of ice crept over some drainage divides and flowed elsewhere. At Tenaya Creek, the glacier made a path into Yosemite Valley. Along the way, the glacial scouring smoothed over domes, ripped up boulders, and tore rocks from the base of cliffs, steepening them, most spectacularly at Half Dome.

One of Yosemite's finest vistas can be had from Olmsted Point, up the Tuolumne Road about eight miles southwest of Tuolumne Meadows. If Yosemite Valley lacks easily accessible features of glaciation, Olmsted Point has an embarrassment of riches. To the north (top photo), Tenaya Lake and Mt. Conness provide a nice example of a glacial tarn (lake) and a horn (a mountain peak "sharpened" by having rock plucked from the base of the cliffs below). The valley containing the lake has a broad U-shaped profile.

To the south, Tenaya Creek plunges deep into the gorge below Clouds Rest and Half Dome. The vast granitic face of Clouds Rest (center of second photo) is scored by dozens of avalanche chutes where masses of snow constantly clear off the rock and prevent trees from gaining root. Farther downstream, Half Dome looms over Yosemite Valley. Glaciers never covered the dome. It took its shape instead from the expansion of the granitic rock as it was exposed by erosion. The expansion took the form of fractures that ran parallel to the surface of the rock (exfoliation), which tends to remove corners and edges. Massive vertical fractures called joints allowed the glaciers below the dome to quarry the rocks from below, forming the stunning vertical face of the dome.

Up close, the evidence of the passage of glaciers is plentiful. Hundreds of large boulders, derived from somewhere upstream, litter the landscape (glacial erratics). The surface of the granitic rock has been scraped and scoured to produce glacial polish, striations, grooves and chatter marks (third photo). If you are more interested in the petrology, the glacial polish reveals incredible details in the granite: flow patterns, dikes, and pegmatite veins are visible everywhere, not to mention huge crystals of feldspar.

Olmsted Point is all about spectacular scenery, but there is much in the way of geological learning opportunities as well. On a field trip, it is not to be missed!