Anywhere Else, They Would be Exceptional: Can you Succeed at this Yosemite Valley Scavenger Hunt?

I've been privileged to visit Yosemite Valley dozens and dozens of times over the years, often dragging students, and sometimes with just me and Mrs. Geotripper. We always revel in the beautiful sights, and study the various moods of iconic features like Yosemite Falls, Half Dome, and El Capitan. But there are many times when I notice other unique geological features that in any other setting on the planet would probably be the centerpiece of a national or state park. They get lost in the grandness of this extraordinary landscape. That is the reason for today's post. If you are ever lucky enough to visit Yosemite Valley, take your pictures of Half Dome and Bridalveil Falls, but keep an eye out for some of these other exceptional rocks and waterfalls.

First up is North Dome (above). Just think about it...aren't you just settling for less when you concentrate on Half Dome? Why not a whole dome? It's there if you know where to look (or you know how to read a map!).

Elephant Rock (above) is tucked away on the canyon rim somewhere where the park service didn't even worry about powerlines spoiling the view of the rock. Even more important: can you see the elephant? After 30 years I finally figured it out...

Silver Strand Falls suffers from "backwards distraction". Some sights in Yosemite are so awesome that you can't do anything but stare. And never turn around to see what is happening behind you. There is an epic sight in the opposite direction and thus you might never notice it...a 574 foot high waterfall! It's especially spectacular in winter when the waterfall may be entirely frozen.

Another sight that gets lost in the shuffle of the big views in Yosemite Valley is Sentinel Dome. It's another "whole dome", and while it is not as imposing as Half Dome, it's a great deal easier to climb. In fact, the trail to the summit is only a mile long, and the view is stunning.

Is it possible to simply not see a 1,180 foot high waterfall? It seems like it would be hard to miss, but that's the case with Lehamite Falls. It has the distinction of the only feature in Yosemite Valley that retains its original Ahwaneechee name. It's not behind some other feature. In fact, it often appears on the edge of shots of one of the iconic waterfalls of Yosemite.

There is another waterfall that can be easy to miss. Staircase Falls can be heard splattering down the cliffs behind a well-known pizza shack in Yosemite, but it often gets missed in the shuffle. It's 1,300 feet high, just short of Upper Yosemite Falls (although it descends in a series of...stairs).

Finally, can you guess the location of this stunning example of exfoliation in action? Exfoliation is the tendency of newly exposed rocks to break in planes that are parallel to the surface of the rock, causing the monolith to eventually take a dome-like shape.

Do you know Yosemite well? What features do you think don't get enough attention by park visitors?

If These Cliffs Could Talk: Tis-sa-ack and Tu-tok-a-nu-la (A Geologic Love Story Redux)

I've been to Yosemite Valley twice in the last month, including a day when the Merced River was still at flood stage. I was reflecting on the many journeys I've made there with my students and with Mrs. Geotripper, and what a stunning place it truly is. I was thinking of a new angle to present some pictures of the latest trips, but then my good friend @phaneritic on Twitter asked a question about quotes concerning the valley that don't involve the writings of John Muir (as wonderful and poetic as his words were). I realized I had written about some of the legends of Yosemite a few years ago, and decided it was time to bring some of them back, in case they were missed before.

These stories also have relevance to the moment because of the decidedly stupid legal war over trademarks being waged between the National Park Service and the recently departed Delaware North concessionaire. One current sign of the ongoing legal battle is the new name for the Ahwahnee Hotel ("Majestic Yosemite") and Curry Village ("Half Dome Village"). Half Dome is a very plain name for such a stupendous rock, and I am thinking the park service missed an opportunity. Tis-sa-ack Village might have been a mouthful to pronounce, but it gives the rock a history and an air of mystery.

And so here it is, the story of Tis-sa-ack and Tu-tok-a-nu-la, a geologic love story, first published in November 14, 2014:

Tis-sa-ack (Half Dome) from near Yosemite Falls

A love story...

Unnumbered snows have come and gone since The Great Spirit led a band of his favorite children into the mountains, and bade them rest in this beautiful Valley of Ah-wah-nee. They were weary and footsore, and were glad to rest after their long journey. Here they found food in abundance. The streams held swarms of fish, meadows were knee-deep in sweet clover, great herds of deer roamed the forests in the Valley, and on the high mountains, oak trees were bending under the weight of their acorns, grass seeds and wild fruits and berries grew in bountiful profusion. Here they stayed and built their villages. They were happy, and multiplied, and prospered and became a great nation.

North Dome, Washington Column, and Half Dome in the clouds

How many stories begin in paradise?

I find the myths of different cultures to be fascinating. They provided their people with an explanation of the unexplainable, a comforting story that suggests there is order in the apparent chaos of the universe. In the perspective of geology, we can sometimes see the whispers of eyewitnesses to significant geologic events: the eruption of Mt. Mazama, for instance, which resulted in the formation of Crater Lake, is described in Native American oral histories. In this post we see one of the legends of Yosemite Valley, with all the embellishments and cultural biases of a 1922 narrative. Still, it's a good story

To their chief came a little son to gladden his heart. They wanted this son to become a great chief, capable of the leadership of a great people. He was made to sleep in the robes of the skins of the beaver and the coyote, that he might grow wise in building and keen of scent. As he grew older he was fed the meat of the fish, that he might become a strong swimmer, and the flesh of the deer, that he might be light and swift of foot. He was made to eat the eggs of the great crane, that he might be keen of sight. He was wrapped in the skin of the monarch of the forest, the grizzly bear, that he might grow up fearless and strong in combat. 

So many stories come with the hero, and the most interesting stories have heroes with flaws...they had everything. But then things happen. The world and the people who live in it are not perfect. And frankly, life would not be interesting.

And, when he grew to manhood, he was a great chief and beloved of all the people. His people prepared for him a lofty throne on the crown of the great rock which guards The Gateway of the Valley, and he was called Tu-tok-a-nu-la, after the great cranes that lived in the meadow near the top. The people of Ah-wah-nee were happy, for Tu-tok-a-nu-la was a wise and a good ruler. From his high rocky throne he kept watch over the Valley and the people whom he loved. He called on The Great Spirit who sent timely rains, so that the acorns grew in abundance, the hunters returned from the forests with game, and the fishermen from the streams with fish. There was peace and plenty throughout the Valley of Ah-wah-nee, and when Tu-tok-a-nu-la held speech with his people from his high throne his voice was deep and strong like the deep sound of the waterfall.

Tis-sa-ack from Sentinel Bridge

But paradise can't last forever. Trouble was coming, or more to the point, the trouble lay hidden in the heart of the hero, and it was about to be made manifest. There were no doubt all kinds of communications between the many Native American bands in California, and the trading of knowledge and technology. I'm sure this led to problems at times as well.

One day as Tu-tok-a-nu-la sat gazing into the glowing colors of the west, he saw approaching his valley a strange people, led by a maiden of wondrous loveliness. He called to them and the maiden answered him, saying, "It is I, Tis-sa-ack. We have come from the land of my people in the far south to visit with you. We have heard of the great and good chief, Tu-tok-a-nu-la, of his great people and his wonderful valley. We bring presents of baskets and beads and skins. After we have rested we will return to my people in the far south." Tu-tok-a-nu-la welcomed the fair visitor from the land to the
south and had prepared for her and her people a home on the summit of the great dome at the eastern end of the Valley. There she stayed and taught the women of Ah-wah-nee the arts of her people. Tu-tok-a-nu-la visited her often in her mountain home. He was charmed by her wonderful beauty and sweetness, and begged her to stay and become his wife, but she denied him, saying: "No, I must soon return with my people to their home in the far south." And, when Tu-tok-a-nu-la grew importunate in his wooing, she left her home in the night and was never seen again.
 

To-ko-ya (North Dome), Nangas (Washington Column) and Tis-sa-ack (Half Dome) from Glacier Point. The Ahwiyah Point rockfall scar is visible just right of center below Half Dome.

The perfect women, the Helen of Troy, the Eve. Of course, perfection is a tricky concept, subject to many biases and assumptions. It doesn't much take into account the actual relationship between those involved. As Mr. Spock mentioned in a famous episode of Star Trek: "After a time, you may find that having is not so pleasing a thing after all as wanting". Bad things are about to happen.

I admit, I've never heard the word importunate before. 

When the great chief knew that she was gone, a terrible loneliness and sorrow came to him, and he wandered away through the forests in search of her, forgetting his people in Ah-wah-nee. So strong was his love for her, and so deep his sorrow, that he forgot to call upon The Great Spirit to send the timely rains. So great was his neglect that the streams grew smaller and smaller and finally became dry. The crops failed. The hunters came back from the forests without meat, and the fishermen returned from the streams empty-handed. The leaves and the green acorns fell from the trees, and the bright flowers and green grasses became dry and brown.

From Washburn Point it is obvious that Half Dome isn't just a boring name, it is a mathematically wrong name. Three-Quarter Dome, maybe. I would just go with Tis-sa-ack

This is where the geologist in me starts paying attention. California has droughts, and there is evidence of mega-droughts that lasted more than a century. Check out this post for some of the striking evidence. These droughts both occurred within the last 2,000 years, recently enough to be remembered in the oral histories of a people.

And then things get interesting in a hurry...

The Great Spirit became very angry with Tu-tok-a-nu-la. The earth trembled with his wrath so that the rocks fell down into the Valley from the surrounding cliffs. The sky and the mountains belched forth smoke and flame. The great dome that had been the home of Tis-sa-ack, was rent asunder and half of it fell into the Valley. The melting snows from the high mountains came down into the Valley in a flood and drowned hundreds of the people. But the wrath of The Great Spirit was quickly spent, and the heavens again grew quiet. The floods receded, the sun shone, and once more peace and calm reigned over Ah-wah-nee. The life-giving moisture from the renewed streams crept into the parched soil. The oak trees put on new leaves and acorns. The grasses again became fresh and green, the flowers lifted their drooping heads and took on their old gay colors. The fish came back to the streams, and the game to the forests.

Wow.

"The earth trembled...so that the rocks fell down into the Valley from the surrounding cliffs". Earthquakes have rocked California for a lot longer than humans have been around, and no doubt played an important part in causing mass wasting within the valley. John Muir experienced the 1872 Lone Pine earthquake while in Yosemite Valley (magnitude 7.8 or higher) and witnessed the collapse of a cliff. I've witnessed a few small rockfalls that I will never forget. Imagine the impact of a really large quake and the accompanying rock falls on the collective memory of a people.

"The sky and mountains belched forth smoke and flame". Yosemite lies just west of the Long Valley Caldera and the Mono Craters, and eruptions have occurred there as recently as a few hundred years ago. Imagine the impact of a fair-sized eruption over the mountains on a people who maybe had never witnessed such a thing, or only heard about it in legends.

"The melting snows from the high mountains came down into the Valley in a flood and drowned hundreds of the people." It's not hard to imagine the impact of a Pineapple Express (an atmospheric river storm) falling onto a thick snowpack in the mountains above Yosemite Valley. Such an event took place in 1997 (be sure to check out the video). Much of the valley floor was covered by as much as 6-8 feet of water, and the event was devastating to the human developments in Yosemite Valley.


Ironically, the natural environment was far less devastated. The ecosystem of Yosemite evolved in an environment of occasional huge floods, and life sprang back quickly.

And, when the Valley was once again clothed in beauty and plenty, there appeared on the rent face of the dome which had been her home, the beautiful face of Tis-sa-ack, where it can still be seen to this day. And the dome was named Tis-sa-ack, in memory of the fair visitor who had been loved by all the people of Ah-wah-nee. At the same time, that all might hold his memory in their hearts, there appeared on the face of the great rock supporting his throne, the majestic figure of the great chief, dressed in a flowing robe and pointing a finger to where he had gone, to El-o-win, the happy land beyond the setting sun.

And thus we have the story of how Half Dome, Washington Column, and North Dome came to be. I am struck by how lifeless these names actually are, and I wish we could see their names changed to reflect the very interesting stories of their origins.

We have stories too of the formation of how these rocks came to be. They involve the formation of granitic magma deep in the hellish regions of the Earth's crust, the intrusion and cooling of the granite, the uplift and erosion of the rocks by rivers and glaciers, and the shaping of the rocks by the working of jointing, exfoliation, ice, and mass wasting. It's a good story, based on careful observations, but the ancient legends? They were based on careful observations as well. The Native Americans maybe didn't have the technology we have today, but they did a pretty good job of describing the phenomena, and designing models to explain their observations. 
 
This version of the Half Dome story is from The Lore and the Lure of The Yosemite by Herbert Earl Wilson, published in 1922. Another legend of Half Dome involves an argument between a husband and wife, with thrown baskets and other unpleasantness. I like the story above better!

Perhaps a Last Look at Some Yosemite High Country (for the Winter, Anyway)

"Half" Dome from Washburn Point

I made the trek up the hill to see Yosemite last weekend, with a field trip on the valley floor on Saturday with my students, and a quieter tour in the high country with Mrs. Geotripper on Sunday. We headed up Glacier Point Road to gain a unique perspective on Yosemite Valley and the higher country above. With a fairly powerful storm arriving tonight, it is at least conceivable that the road could close for the winter due to snow. There was certainly a mood of closing down. The road was uncrowded, and so were the parking lots. The curio shop at Glacier Point was closed for the season.

Yosemite high country, with Mt. Broderick, Liberty Cap, and Nevada Fall in the foreground.

Many people who travel to Glacier Point tend to be single-minded in their quest, and often miss one of the truly spectacular viewpoints the road has to offer: Washburn Point. It is perched at the 7,400 foot level above the Merced River directly across from "Half" Dome. It is from this point that the misnomer is most obvious. If anything, Half Dome should have been named "Four-fifths Dome".

Nevada Fall on the upper Merced River

There is a stupendous view towards the high country of Little Yosemite Valley and the headwaters of the Merced River. The effect of glaciation is apparent everywhere. Glacial stairsteps, caused by pervasive vertical fractures in the granite ("joints"), were the origin of the two major waterfalls on the Merced River, Nevada Fall (594 feet, above), and Vernal Fall (317 feet, below). Along the skyline above, the glacially-carved horns, aretes, and cirques can be seen. It's wild and beautiful country.

Vernal Fall from Washburn Point

I imagine Washburn Point gets less traffic than Glacier Point because it doesn't look down on the main part of Yosemite Valley. That's okay with me. It's notable that not a single road is visible from Washburn. One is looking at wilderness, something that is sorely lacking in the more populated parts of Yosemite National Park.

North Dome and Basket Dome on the north side of Yosemite Valley. Mt. Hoffman rises in the distance.

Finding Peace in the Nation's Most Crowded Park: A Walk Through Yosemite Valley

If you've read my previous couple of posts, you know I was in Yosemite Valley over the weekend. I was guiding my students on a field trip up the Merced River and into the park on Saturday, and I came back on Sunday seeking some better pictures of the recent rockfall at El Capitan.

We can't park a big bus just anywhere on the floor of Yosemite Valley, so I had to let my students loose to find their way to the upper end of the valley using the free trams. There was enough time that I decided to walk the three or so miles from Yosemite Lodge to Happy Isles, picking whatever winding combination of roads, trails, or sandy river shoreline I could find (there's a direct route, but why stick to that?). I was almost immediately awarded with a nice view of Yosemite Falls, which at 2,425 feet is about the seventh highest waterfall in the world. To my surprise, there was a bit of water flowing, kind of unusual this late in the fall.

The fall colors may not match the technicolor splendor that happens in the hardwood forests of the eastern U.S., but then those forests don't have the backdrop of vertical granite walls that Yosemite has. I was reveling in the splash of color here and there. I often think that fall is my favorite time of year here.

I made my way across the meadow trail to Sentinel Bridge. The cliffs of Glacier Point loomed high above. I didn't realize that I'd be up there looking down the very next day (that will be another post).

Half Dome seems to loom over every meadow view in the valley. It rises 4,800 feet above the valley floor. Although glacial ice filled the valley to the rim, Half Dome stood above the frozen rivers. It was shaped by exfoliation sheeting (corners and edges snapping off), as well as a bit of undercutting from the glaciers below. As you will see in a near future post, Half Dome would better be called Four-fifths Dome, but that doesn't flow so well. Actually I prefer the Native American name of Tis-sa-ack ("Crying Girl").

Because people tend to stare at Yosemite Falls when they are flowing, they find it easy to miss the prominent cliff of Yosemite Point and the Castle Cliffs (below).

I crossed the Merced River at Sentinel Bridge, and got a colorful version of the iconic view of Tis-sa-ack reflected in the still water.

It's the funniest thing...the seven square miles of the floor of Yosemite Valley may very well be the most crowded real estate in the national park system. The park doesn't get the highest number of visitors in the system, but it does get five million, and something like 90% of them spend their visit in the valley. And yet, despite the crowds on the day I was there, the moment I got off the road, I invariably found myself alone. Finding peace in the middle of tourist chaos is a precious gift, and I soaked it in.

Approaching the footbridge near the empty Curry Housekeeping Camp, I had a fine view towards Yosemite Point and the Castle Cliffs reflected on the Merced River.

I quickly walked through the gaggle of people at the stores in Curry Village (I'm not a purist; I stopped for a Gatorade at the store). I headed up the trail to Happy Isles. I started to find more and more Dogwood trees turning shades of pink and yellow. I made it to the Nature Center and met with my students to talk about geology, and then we made our way back to Yosemite Lodge.

While I was talking to the students one last time, I happened to turn and saw the Moon rising along the cliffs off to the southeast. I snapped some zoomed pictures, only to find later that I was aiming directly at Glacier Point. If you look closely, you can see the fencing and people gathered on the edge of the precipice. I was pleased with the effect.

We got on the bus and headed home, and despite the hubbub of running around with students all day, it was one of the most serene experiences I've had in a while. And best of all, I would be up there again the next day!

A Series of Fortunate Events: Glacier Point, Living Up to the Hype

Glacier Point on the rim of Yosemite Valley is hands-down one of the most spectacular places one can stand in the world. There's just no place like it. And it's noisy. It's crowded. There is a busy and often full parking lot. And despite that, it is worth putting up with, because there just aren't that many places where you can look straight down for 3,000 feet, and at the same time see the iconic rocks of the upper valley from a unique angle.

It takes a little effort to get there. One has to drive about 25 miles from the floor of Yosemite Valley up a narrow winding road. One has to wade through the crowds to get the edge of the precipice. But no matter how many times I've stood there, I can never fail to be in awe that such places exist. In one sweeping view one can see the north valley wall from the vicinity of the Three Brothers and Yosemite Falls, past Yosemite Point, on to North Dome and Basket Dome, across the deep trough of Tenaya Canyon to Half Dome. And below your feet there is the floor of Yosemite Valley, the meadows, the forests, the parking areas, the resorts, all from a nearly vertical perch at 3,200 feet (980 m).

It's from a high point like this one that I can best appreciate the work of the glaciers that altered a narrow river-carved canyon into the wide, flat floor we see today. The earliest glaciers filled the valley to the rim (the Pre-Tahoe stage around 800,000 years ago), while the later advances only filled the valley to one-third or so of the total depth (the Tahoe stage at 130,000-65,000 years, and the Tioga stage from 20,000 to 13,000 years ago). The domes, like North Dome, Basket Dome and Half Dome, rose above the ice at all times. Their rounded shapes are the result of exfoliation, the tendency of slabs to break off the edges and corners of solid monoliths of granitic rock as erosion took weight off the surface of the rock. Glaciers helped excavate the rock from the jointed face of Half Dome, but never overtopped the gigantic rock.

One might think that a view like this is unchanging on a human time scale, but that's not exactly true. It's a little tricky to see it in the shadows, but look at the whitish exposure of granite to the left of Half Dome in the picture above. That scar didn't exist prior to 2009. Every visitor prior to March of that year saw something different. The Ahwiyah slide involved thousands of tons of rock that fell 1,800 feet to the floor of Tenaya Canyon. The resulting explosion of rock destroyed hundreds of trees on the valley floor. To see some before and after pictures, click here for a look.

Our class finished at Glacier Point and headed back the vehicles, but we weren't done with standing in dramatic places. That will be in the next post!

A Series of Nearly Unfortunate Events: Fall in Yosemite National Park

Oh jeez, that's not something one likes to see on a field trip...

How many horror movies begin with people ignoring the warning signs, both literally and metaphorically? The doomed characters doggedly soldier on, minor disasters mount, and then major disasters. Today felt a little like that. At our second stop, two CHP units took up positions on both sides of the bus. Uh-oh...

It turned out they were there for the cow which had escaped the nearby pasture. We helped herd the wayward bovine back inside the enclosure.

We passed the continuing effort to contain the huge Ferguson Slide, which collapsed into the Merced River and across Highway 140 nearly ten years ago. It's been completely covered with boulder containment nets, and they are apparently ready to start work on the rock shed that will allow future rocks to roll over the road and into the river.

And then the first of the menacing signs. The rain had started falling, a true blessing in the drought, but why during our field trip? Because it was maybe a metaphorical sign, of course! Don't go on!

But the next sign said not to stop! What were we to do? 

There were fires burning next to the road, and after all the horrific wildfires of last summer, one could hardly resist the urge to call and report the fire. But the signs said not to report! What were they trying to hide?

Sorry for the blur. We couldn't stop!

The actual reason for the fire of course was to try to bring the valley floor back into some kind of reasonable ecological balance. Fires had been suppressed on the valley floor starting when the park was established, but this turned out to be a bad idea. So many trees grew that the forest was too thick and full of fuel that a wildfire could have destroyed all the trees, not just some of them. By burning the forest when conditions are safe, the troublesome trees can be controlled without destroying the mature trees.

So we pressed onward, farther into the valley through rocks, wind, rain and fire, just daring the elements to interrupt our geological field studies. And then we found incredible things! The storm relented for a few moments at at time and the cliffs and towers of Yosemite began to peek out from behind the clouds.

The fall colors were starting to appear here and there...

The clouds provided an interesting contrast to the forests and cliffs...

And at Yosemite Falls, we saw something precious and rare: flowing water. Two days of rain had rejuvenated the iconic waterfall, which had been dry since early summer. All in all, a challenging day, but also a spectacular day. And no crazed axe murderers!

What Lies Beneath Yellowstone? Yosemite, of course!

Upper Yosemite Falls, 1,250 feet high. Taken together the three components of Yosemite Falls amount to the fifth or seventh highest waterfall on the planet, at 1,425 feet (depending on who is measuring).

Okay, it's more fair to ask "what lies beneath Mt. Rainier or Crater Lake?". Yellowstone National Park sits atop a continental hot spot, and the plume of hot material will either explode out in a violent rhyolite tuff eruption, or cool deep underground into a granitic pluton. And Yosemite National Park exposes a great deal of granitic rock. But the origin of the granite at Yosemite is more related to arc magmatism, the formation of volcanic and plutonic rock as a plate of oceanic lithosphere sinks into the mantle beneath the edge of a continent. That's what is happening today in the Cascades, and it's what formed the famous volcanoes of that range: Rainier, Hood, St. Helens, Crater Lake, and more than a dozen others.

Lower Yosemite Falls, 320 feet high. Note the people for scale.

In a way, today's post is a sneak preview of the ending portion of my certain blog series on "Driving Through the Most Dangerous Plate Boundary in the World". The Franciscan subduction zone that was active during the Mesozoic Era was responsible for forming the Sierra Nevada batholith (batholith is a term for large bodies of magma, or a combination of numerous plutons in a region). The neat thing one can consider when visiting a Sierra Nevada park like Yosemite is that not only are you standing on the underside of former volcanoes and calderas, but you can also imagine the dinosaurs that once tromped around on the slopes of said volcanoes (we have even found fossils of a few of them, down in the sediments of the Great Valley)!

The Cathedral Rocks. Bridalveil Falls lie hidden on the other side.

I was in the valley again on Saturday, working through the onerous chore of dragging students around on a geology field trip. Somebody has to do it, after all. Buses can only stop in a couple of places around the valley floor, so we got off the bus and used the valley tram system to make a series of appointments at several spots in the valley to discuss the very cool geology.

The Middle Brother slide, from 1987. It is the largest slide in Yosemite's recorded history

Given a choice, I usually fore-go the tram in favor of walking to the appointment spots. It's not that I don't like the trams; they make a big difference in traffic congestion on the valley floor (you think it's crowded today? Imagine all the people on the trams in individual vehicles...). But because the trams make around thirty stops while traveling the loop of 8 or 9 miles, I can progress as fast or faster on foot. So I hoofed it from Yosemite Lodge to Happy Isles, a distance of about four miles. I had an hour and twenty minutes to get there, and I arrived with not a second to spare. But I saw marvelous sights along the way!

Yosemite Falls was at what may be the best flow it will have all year (top two photos). The drought left the park with 5% of its normal snowpack, and much or most of the ice is already flowing down the creeks and rivers. The falls will be dry in early summer.

I walked south from Yosemite Lodge where I had some very nice views of the Cathedral Rocks and the Middle Brothers Slide. The slide took place in 1987, and was the largest slope failure in Yosemite's recorded history, with over a million tons of rock.

Washington Column, the Royal Arches, and Clouds Rest

Washington Column, the Royal Arches, and Clouds Rest make for an awesomely steep gorge from the perspective of Swinging Bridge. The Bridge doesn't swing anymore, darn it! But it makes a nice platform for viewing Yosemite Falls and Yosemite Point from some distance away. The Merced River should be a bit more riotous at this time of year.

Yosemite Falls and the Merced River from Swinging Bridge

I added one small new section of trail to my experience this day. The Yosemite Loop trail travels the length of the valley on both sides, and I have walked most of it, but the section from the chapel to the LeConte Memorial Building was new to me. Despite the dry conditions, the forest floor was green and bursting with small white flowers.

From the south side of the valley, Washington Column stands as a bold cliff like the prow of a mighty battleship. It is shaped by joint fissures, large vertical cracks formed when the rock was exposed by erosion and expanded. North Dome, high above the Column, was formed by a similar process called exfoliation, where the rock expanded outwards, breaking off slabs that are parallel to the surface of the rock. The process tends to form domes all across the Sierra without the action of glacial erosion. The slabs formed by exfoliation can be dangerous to humans. In 1996, a slab the size of a football field came off the valley rim near Glacier Point, and collapsed on the valley floor near Happy Isles. The rocks killed one person and severely injured another. I was racing to the appointment at Happy Isles to show the students the site.

It was a beautiful day on the valley floor, and it was the first time some of my students had ever visited the park. That is one of the great privileges I have as a teacher of geology, introducing them to such a wonderful place, and providing an in-depth story explaining how the place came to exist. And dinosaurs!