A Series of Hopefully Fortunate Events: Saying Goodbye to Yosemite's High Country (for now)

Our field studies trip to Yosemite National Park reached a climax when we reached Tioga Pass (9,943 ft / 3,031 m) at the east end of the park. The pass is the highest highway route in the state (a paved road in the White Mountains and the Bristlecone Forest reaches just a few feet higher, at 10,075 feet). The scenery at this elevation is spectacular. The surrounding peaks reach over 13,000 feet (nearly 4,000 meters), and glaciers have scoured much of the terrain to barren rock. Few trees can survive in this harsh environment.

There is not much in the way of granite east of the pass. The white expanse of plutonic rock in Tuolumne Meadows has given way to older, darker rocks that began their existence as volcanic rocks and oceanic sediments more than 200 million years ago. They have been baked and deformed by deep burial in the crust. There is also the remains of a caldera, a giant collapse depression similar to the one that formed Yellowstone or Long Valley, but in this instance we are seeing it from the base, the part that was once a mile or two underground.. 

This was the source region for the glaciers that scoured the Grand Canyon of the Tuolumne and Yosemite Valley. Numerous cirques, horns and aretes can be seen along the Kuna Crest and the main Sierra Crest. There are even a few small glaciers tucked into the high canyons (Dana Glacier is accessible by trail).

It was the end of our field studies course, and I fervently hope that it will be the last chance of seeing Tioga Pass. For a while anyway. I had the fascinating but unfortunate privilege of seeing Tioga Pass on an early January day in 2012, because there had been no snow. It was strange walking across a solidly frozen Tenaya Lake (visible in the top picture) in a t-shirt and jeans when there should have been 10-15 feet of snow everywhere. We've had a disastrous run the last four years with an unprecedented drought, the worst in many generations, even centuries. There is hope that El Nino conditions in the Pacific Ocean will bring on more than the normal amount of rain and snow, but that remains to be seen. There have been a few weak storms already, and another system coming in Monday. Some hopefully fortunate events, as it were.

As beautiful as it is, I hope I won't have another chance to see Tioga Pass until May at the earliest.

Driving Through the Most Dangerous Plate Boundary in the World: The "Dr. Who" of Mountain Ranges

The Whitney Crest of the High Sierra. Mt. Whitney is just out of sight to the right.

I was torn over the title for this addition to the "Driving Through" blog series. I thought of taking the zombie approach and calling them the living dead mountains ("they keep coming at you"), or the crazed killer angle ("they're never truly dead"), but these seemed...um...overly negative for a mountain range that I love. Then it occurred to me that there is a well-loved media character who is regularly mortally wounded and is regenerated with a new body. And Doctor Who is certainly loved by millions of rabid fans. And that seemed a good analogy for the Sierra Nevada of California. The mountain range has been uplifted, deeply eroded, rejuvenated, eroded, and risen yet again, and the mountains have been different each time.

Tenaya Lake and Mount Conness in Yosemite National Park

The are at least three different mountains that occupied this part of California in the last 400 million years, and most of them were related in some way to convergence, the subduction of sea-floor lithosphere beneath the western edge of the continent. The most recent incarnation of the Sierra Nevada has an enigmatic origin, and many uncertainties remain about the specific mechanics of uplift. But rising they are, even to the present day.

Highly deformed calc-silicate metamorphic rocks in Kings Canyon near Boyden Cave.

The earliest mountains were related to the collision of exotic terranes with the western edge of North America. Some of the rocks had their origins in early Paleozoic time, and were severely deformed during the Devonian period roughly 400 million years ago. Some researchers have related the deformation to the Antler Orogeny that is best revealed in central Nevada. Had one been there at the time, the scene might have been reminiscent of some of the complicated island arcs in Indonesia.

Highly folded slate near Dial's Rock Shop near Mariposa, west of Yosemite National Park

By Triassic time, about 250 million years ago, subduction zones were directly active along the west coast of North America, and chunks and bits (the exotic terranes) became incorporated into the continent itself. Mountains were pushed up along the coast in much the same way as mountains have formed in southern Alaska, but without the glaciers. The edge of the continent was located closer to the equator than today.

Mt. Shasta, in northern California, as a stand-in for the Ancestral Sierra Nevada

By late Jurassic time, about 150 million to 85 million years ago, the so-called Ancestral Sierra Nevada mountains pierced the sky. Subduction was feeding vast batholiths of granitic rock deep in the crust, and large volcanoes and calderas caused mayhem at the surface. These mountains may very well have resembled today's Andes Mountains, and indeed, the margin at that time is referred to as the Andean-style plate margin. And then...the mountains died away again. A massive erosional unroofing began that removed 5-6 miles of overlying rocks, exposing the granitic rocks. Evidence strongly suggests that the mountains had been laid low, to mere hills (although contradictory research exists). Sedimentary rocks from 40-50 million years ago show a system of coastal marshes and estuaries, sandy beaches, and large rivers with sources in at least central Nevada, and possibly farther inland.

Much of the western Sierra Nevada is composed of gently sloping, deeply eroded metamorphic rock, covered here and there by volcanic mudflow deposists (lahars), and ash tuff.

It's only been in the last few millions or tens of millions of years that the present-day Sierra Nevada began rising to their present-day prominence. The mountains rose as a westward tilted block, outlined by major faults on the east side, and the Great Valley of California to the west. As the mountains rose, deep valleys were carved by the westward flowing rivers like the Kings, Merced and Tuolumne. In the last two million years, global cooling brought about a series of ice ages, and glaciers scoured the upper parts of the river valleys, giving rise to the spectacular gorges that we visit today, Yosemite Valley being the epic example.

Yosemite Valley from the vicinity of Turtleback Dome.

So, our drive through the most dangerous plate boundary in the world will continue, following pathways into the heart of this mountain range that is both ancient and youthful at the same time.

Out of the Desert and Back to the Green Hills of Home

Today wraps up the story of a week-long journey through the deserts of the southwest. I've been telling the story as if in real time, so it sounds like I'm just now arriving home, but actually we finished the trip just over a month ago. It's a time warp of sorts. I'm about to leave on another trip, this time to British Columbia and Alberta.

Coming home. You can live in a boring place, a place that is the worst in the country even, but coming home is coming home. There is the familiar kitchen, the television, the well-worn couch. The weeds. The office. To me, home is something bigger. It's the landscape that surrounds my home region. Basically those places within a day's drive that I've seen over and over. My home starts at the summit of Tioga Pass in Yosemite National Park. It's a three hour drive from my house, but a trip doesn't really begin until we've gone over the summit, and on the return trip we feel home the moment we get there.

Compared to the dry lands we had just explored, the mountains have a richness of moisture. It's not nearly what it should be, for we are still in the grip of a horrendous drought, but some late spring snow was still lingering in the high places. We felt such a relief at the sound of babbling creeks.

Tuolumne Meadows is the accessible part of the Sierra Nevada crest in Yosemite National Park. The meadows lie at 8,000 feet, and the surrounding mountains reach elevations of just over 13,000 feet. This region was the source of glaciers that scoured the deep U-shaped valleys of Yosemite and Hetch Hetchy. At one time there was an ice cap at Tuolumne that was more than 2,000 feet thick that spilled out in several directions, including Tenaya Creek which holds beautiful Tenaya Lake (top picture).

John Muir talked about the Sierra Nevada high country as the "gentle wilderness", and that's been my experience most of the time. I've seen violent storms across the Basin and Range and Colorado Plateau, and some have been terrifying because we were camped out there and had nowhere to hide or take shelter. If a storm blows in while I'm exploring Yosemite, well, we just jump in the car and go home. We can come back the next day.

We had already driven three hundred miles this day, so the sun was getting close to the horizon. Photographers say that evening and morning are the best times for good shots, given the nice contrasting shadows instead of the washed out colors from a noonday sun.

There was a storm over the Basin and Range that we had just skirted. We got a few drops, almost enough to turn on the wipers. From a distance it looked menacing. But all was calm for us in the meadow.

We made a last stop at Olmsted Point for a look at the sunset on Half Dome. We then headed down the hill, and returned to our home. It was nice to be back, but of course a few days of sloth and we wanted to get on the road again. We are restless souls sometimes!

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.

The Right Place at the Wrong Time: A January Day at Tioga Pass

If anyone had told me anytime in all the years that I have lived here in Central California that I would be where I was today, I would not have believed them. It just doesn't happen. Tioga Pass in Yosemite National Park always closes in November or early December. Always (ok, in 2000 it was open for one day in January). Everyone in the Sierra knows that the pass closes and no one gets to go up there except for the hardy cross-country skiers until May or June. But that's the kind of year we are having here in California; water managers should be terrified. The snowpack is at 15% of normal, and after today, I'm saying "What snowpack?"

So off we went today, to see what we could see. There have been few storms yet this year or last, but it is plenty cold. Cold enough that Tenaya Lake and all the other high country lakes and ponds are completely frozen over. If you click on the photo above, you'll see ice-skaters out on the lake. It is a strange sight to see; frozen lakes, but no snow to speak of on the surrounding peaks.

Being a Californian born and bred, I admit to not knowing much about the dynamics of lakes freezing over, but I am pretty sure that these are pressure ridges caused by expansion of the surface of the lake as it freezes. It was a fascinating thing to see.

Oddly enough, the temperatures were in the forties and fifties, and I wore a short-sleeved shirt all day. We drove past Tenaya Lake and made our way to Tuolumne Meadows. Again, there was ice everywhere, but no snow other than scattered patches in the forest. The moon rose over Cathedral Peak (or is that Unicorn?)

Tuolumne Meadows was pretty as always, maybe even more so. I was happy to be able to visit in January, an absolutely new experience for me. I just worry about what this means for our water supply this year. These are Texas kinds of numbers, drought-wise, and no storms are in the long-term forecast.

We stopped at the top of Tioga Pass. On January 5. It was beautiful. And weird. Standing at 10,000 feet in the dead of winter and not dying of hypothermia. The last time my ancestors did something like this, very bad things happened (hint: my ancestors included the Donner family...look it up if you don't know the story).

Heck, we came this far, why not cross the Sierra? We headed a few miles down the road towards Lee Vining. We were tempted to hit the Whoa Nellie Deli for dinner, but we realized that an incredible sunset might be developing. We turned around and headed back towards Tioga Pass, but not before snapping a picture of Ellery Lake (also completely frozen over).

We stopped to walk on the Dana Fork of the Tuolumne River (below). The silence of the frozen landscape was eerie. No water was flowing anywhere.

 A lenticular cloud formed over the Sierra Crest. Or was it a UFO?

One more oddity. We did have an unusual storm earlier this year. It involved no rain or snow, but it did include hurricane force winds. Driving down from Tioga Pass I noticed hundreds of Lodgepole Pines that had been literally ripped from the ground. They were all pointing west. Again, an eerie day.

We headed back to Tenaya Lake and Olmsted Point to see how sunsets differ when the sun is setting far to the south of where it sets in summer or fall. Look for it in my next post.

Friday's Fun Fotos: the Fluvial Forest Discussed

I posted some pictures of a "fluvial forest" this morning (fluvial=river) asking for an explanation about how these trees came to exposed in the river channel, and in short order got three excellent answers. I've provided a larger format picture above to give some perspective on the setting (click on the image to see the bigger picture). This is the West Walker River, a few miles downstream from the junction of Highway 395 and Highway 108 from Sonora Pass in California's Sierra Nevada.

It's rather striking and strange to see so many trunks of mature trees sitting in the active channel, as Jeffrey pine really can't tolerate soaking for more than a few weeks a year. They otherwise do quite well on the shady slopes to the right in the picture above (and not so well on the dry slopes to the left). I have to admit that this was my thesis area, but I didn't really give the trees much thought 25 years ago, yet they reveal an interesting story.

Anne had a great idea, saying that mining wastes could have caused the filling of the channel, smothering the trees. This would be a great explanation, and such a thing indeed happened in the Sierra Nevada during the hydraulic mining era of the Gold Rush (I posted a picture of a tree trunk formed this way some time back). The problem is that no mines of any consequence were present in the area.

Rob provides a glacial explanation, in which glacial outwash buries a forest, and then a surging glacier planes off the trunks. This is an appealing explanation because this part of the canyon was very close to the terminus of the Tioga and Tahoe glaciers. Glaciers would explain it, except the age of the trees are wrong. One set of the trees in this fluvial forest grew between AD 900 and 1100, while another set grew between AD 1210 and 1350. Smaller glacial episodes in the last two thousand years never approached the area.

Lockwood comes the closest to explaining what happened here, suggesting that a debris flow filled part of the canyon, killing and burying the trees, and then the river exhumed the forest. But there is an interesting twist: the valley is really narrow here (look at the top photo; there is barely enough room for the river and the highway, and when the river floods, there is no room for the highway at all. It disappears and has to be rebuilt, most recently in 1997). The trees, and there are dozens of them, were pretty much filling the entire canyon bottom. There was almost no room for a river channel when these trees were growing. This suggests that the river was much smaller in the two time periods the trees represent. In other words there were two crippling droughts that lasted 200 and 140 years respectively. Once the droughts ended, the river filled the channel with sediment again, and debris flows, as Lockwood suggests, undoubtedly had a role. Outwash from the Matthes glaciation may have been a factor as well.

There is confirming evidence for such mega-droughts in other areas of the Sierra Nevada. Tenaya Lake, Lake Tahoe, and Fallen Leaf Lake all have submerged forests that grew to maturity during these periods when the lakes didn't have enough water to breach their outlets. Oral histories of California's Native Americans also hint at terrible droughts.

In human time frames, droughts are a fact of life here in California. We had extended droughts from 1928-1934, 1960-61, 1976-77, and 1988-92. We may or may not be ending a three year drought this year as well. Our population has grown so large that each drought becomes more problematic, and we muddle through on the strength of a few extraordinary precipitation years that fill reservoirs for a time. What would we do if another century-long drought were to come? And what role will anthropogenic global warming play? I, for one, wouldn't particularly care, because I will be dead, but my grandchildren might have a real struggle.

Stine, S., 1994. Extreme and persistent drought in California and Patagonia during mediaeval time. Nature 369:546-549. I can't find a copy of Stine's paper on the web, but Stine's findings are discussed briefly here (page 15-16), and here (page 296)