The Sentinels of Yosemite Valley: Giving Them a Bit of Respect

Let's consider for a moment that this is anyplace else in the world. You look up and see a waterfall that is 1,920 feet high, falling in six major steps. In what place in the world would this not be a notable feature with a state or national park designation? In what place would there not be thousands of people visiting every day, snapping pictures and oohing and aahing?

There are no parking lots and viewpoint for this waterfall. As a rule people barely notice that it exists. If that seems astounding, then take this as evidence of the extraordinary nature of Yosemite Valley. 2,000 foot high waterfalls disappear into the scenery. The name of this particular one is Sentinel Falls.

I admit that part of the reason Sentinel Falls is not as celebrated as some is that it is seasonal, flowing principally in the spring season. It's usually dry by the beginning of summer when most tourists visit the valley. But when it is flowing, it is spectacular.

Sentinel Rock suffers the same kind of locational insignificance. In any other part of the world, a 3,000 foot high sheer cliff would elicit awe and wonder. In Yosemite Valley there are so many dramatic cliffs that Sentinel gets lost because people are trying to get a glimpse of Yosemite Falls on the north rim of the valley. Sentinel Rock and the adjacent Sentinel Falls are on the south side of Yosemite Valley, almost directly across from Yosemite Falls. Yosemite is the waterfall that catches their attention.

That's not to suggest that Yosemite Falls doesn't deserve the adulation it receives. The waterfall is 2,425 feet tall, somewhere around the fifth to seventh highest in the world. It always has more water than Sentinel does, and in many ways it is more dramatic. But when I was taking pictures of Sentinel last week in the rainstorm, I was the only person standing in my little corner of the floor of Yosemite Valley. I didn't have to share my moment with throngs of tourists all staring at the same feature and snapping the same pictures from the same angle. It was just me and a quiet moment in an often crowded and hectic place.

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?

El Capitan Rockfall: Alternate Views, and a Realization That This Wasn't the First TIme

El Capitan and the September rockfall from Taft Point on Oct. 29, 2017

Yosemite Valley changed geologically on September 27 and 28, and as I noted in my previous post, the valley will never look the same again. A series of rock falls resulted in a new scar on the east face of the east wall of the El Capitan cliff that can be seen from many points within the valley, including the iconic Tunnel View.

September rockfall from Taft Point on Oct. 29, 2017

I finally got to Yosemite Valley on Saturday, and got a few photos from the Tunnel View that I posted yesterday, but I was with students on a bus. Buses aren't allowed to stop just anywhere in the valley, so I was anxious to get back to the valley in my own car, and Mrs. Geotripper was all for visiting the valley, so we went back up there yesterday. The question, of course, was where to go for a good look? I definitely wanted an aerial view, so we headed up Glacier Point Road, the only route that allows for views from the rim of Yosemite Valley. Glacier Point offers views beyond belief, but only of the upper end of the valley. For a view of El Capitan, the "easy" choices are to hike to the top of Sentinel Dome, or to hike to Taft Point. Both hikes are about a mile and are not overly difficult. Sentinel is farther to the east and doesn't provide as good an angle on the cliff face that fell, so I headed out to Taft Point as the sun approached the western horizon.

The view is striking. The rocks let loose from well over a thousand feet over the valley floor. According to Greg Stock, geologist for Yosemite National Park, the biggest slab (out of seven total), was 394 feet long, 148 feet wide, and between 8 and 28 feet thick. That's bigger than a football field. It had a volume of 10,250 cubic meters, and weighed about 27,675 metric tons. If these numbers and dimensions seem incredibly exact, there's a reason. As Greg Stock explains, in an informative research paper, the walls have been mapped in three dimensions by a form of radar (lidar), and in the aftermath of the rockfall, the walls at the site of the fall were mapped again. The difference in volume could then be calculated.

El Capitan from Taft Point in 2005

I was at Taft Point in 2005, taking pictures of course, and one can compare the appearance of the cliff prior to the event in September.

Horsetail Falls area and future site of rockfall in 2005

The rockfall is also apparent from many spots on the valley floor. We headed to El Capitan Bridge, which offers an excellent straight-on view with the Merced River in the foreground. The white scar is unmistakable.

The Horsetail Falls cliff on Oct. 29, 2017

The difference between before and after couldn't be clearer. It's easy to miss the scale on cliffs this grand...remember, the missing slab of rock was bigger than a football field.

The cliff near Horsetail Falls in 2016

Another way to get a sense of scale is to add the 3,000 foot cliff of El Capitan to the scene...

El Capitan and the Horsetail Falls cliff on October 30, 2017

As I was going through my old pictures, I came to realize that slides have come off this particular cliff in the past. I actually witnessed one of them in 2010 when I was lounging on the granite near the top of Sentinel Dome across the valley. When I say "witnessed" I mean I heard the commotion first, took a moment to realize what I was hearing, jumped up, scanned up and down the valley, and finally thought to turn on the camera and take a few pictures of the rising dust plume.

Dust plume from the 2010 rockfall east of El Capitan

My account of that event can be found here: http://geotripper.blogspot.com/2010/10/rock-fall-near-el-capitan-in-yosemite.html. One can see in the picture below that the 2010 fall was just below the slab of rock that came down in 2017. One can imagine that the stresses on the cliff above were complicated by the event several years earlier.

A Series of Fortunate Events: Why Settle for Half a Dome When You Can Have a Whole One?

Imagine standing at one of the most famous park viewpoints in the world. Ask people standing in that place, the Wawona Tunnel Overlook at Yosemite National Park, how many granite domes they see, they might say just one. If they're feeling humorous, they might even say not just one, but half of one (let's discuss that point). But there are actually two of them. Sentinel Dome is the other somewhat less prominent dome, off to the right of Half Dome (see above).

The hike to the summit of Half Dome is the stuff of legend. One must start very early in the day, hike seven or so miles to the summit pitch (climbing 4,000 feet in the process), and then trudge up a terrifying set of cables and steps on an impossibly steep flank of the dome. People have even fallen off the trail to their deaths. I've not yet had the privilege (of hiking, not falling), but hope springs eternal!

Sentinel Dome is also climbable, but it is not nearly as taxing to the body and soul. It's only a few hundred feet shorter than Half Dome in elevation, but it is also close to the Glacier Point Road, so hiking to the summit is more of a short stroll than an all-day expedition. And it has a marvelous perspective on Yosemite Valley and the surrounding territory.

The official trail starts at the parking lot for Taft Point and Sentinel Dome trails. Get there early in the day because the parking lot fills quickly. These are popular trails. The hike to Sentinel is a mile, but if you are good with topographic maps, you can find an alternate route that is only half as long, and the parking area for the alternate way is almost always empty.

Which ever way you go, the trail passes through an open forest of Ponderosa and fir trees. As you near the ridge top, the sky opens wide and one can sense the huge chasm that lies beyond.

The summit area of Sentinel Dome is relatively barren of vegetation, and is instead an island of granitic rock rising out of the forest. The dome was not formed by the shaping effect of glaciation, and indeed glaciers never covered the summit. The rounding occurred because of exfoliation, the tendency of slabs of granite to break off of edges and corners. Walking the summit pitch one steps over the slabs like a stairway (below).

Exfoliation slabs on the summit pitch of Sentinel Dome

The exfoliation occurs because the granitic rock forms by the slow, slow cooling of silica-rich magma deep in the Earth's crust. The rock expands as it is exposed by erosion near the surface and fractures outward. The process still occurs in the region today. I've witnessed rockfalls from this very spot (see here for the story), and I posted last year about an exfoliation event in Twain Harte.

The view from the summit of Sentinel Dome is nothing short of spectacular. The Cathedral Rocks and El Capitan dominate the view west, while the Sierra Nevada foothills slope away in the distance towards the Great Valley.

East and south, the view takes in the high peaks of the Sierra Nevada Crest and the Clark Range.

Half Dome and Cloud's Rest dominate the scene to the east. Tenaya Canyon and Little Yosemite Valley lie in the shadows below. Yosemite Falls, had it been flowing, would have been visible to the north.

There used to be an iconic tree, a windblown Ponderosa Jeffrey Pine, at the summit. It appeared in many National Park Service photos. A vandal girdled the tree with a knife, killing it. Even here, people can be jerks and worse.

I took a 360 degree panorama with my video camera. It's linked below if you'd like to take a look!

We hiked back down to the cars and drove to the valley floor. The class was about the geology of Yosemite National Park, which encompasses over a thousand square miles. Yosemite Valley covers only about seven square miles, so we spent a surprisingly short period of time down there. We were headed for the high country, which we'll cover the in the next post!

If These Cliffs Could Talk: A Sentinel People Sometimes Miss in Yosemite

If you saw this picture out of context, perhaps in the opening frames of an adventure movie, you might think of this cliff as being an otherworldly precipice full of allure and mystery. Maybe dragons perch on its summit, maybe buried treasure lies in a cave at its base. It's an incredible rock tower.

To back up and look at this cloud filled world from a distance takes away none of the mystery. Here is a spectacularly deep gorge with dark forested slopes and vertical rock cliffs. What kind of place is this? Who's been keeping it such a secret? Shouldn't it be a national park or something?

Well, actually it is, and upwards of four million people look at this cliff tower every year. They just don't quite see it as it gets lost in the multitudes of other more iconic cliffs like Half Dome, El Capitan, and Cathedral Rocks. Half Dome would be in the picture above were it not for the clouds.

We are looking at Sentinel Rock, and it is the hard-to-see tower in the dead center of the picture below. Can you see how easy it is to lose it in the grandeur of the cliffs that surround it on all sides? I was taking advantage of the cloud cover to get a photo from Tunnel View that highlights the cliff.

How could you miss it? It's in the dead center of the photograph! (May 2014)

Sentinel Rock is composed of the Sentinel Granodiorite, which was intruded about 95 million years ago, making it one of the younger intrusive rocks exposed in Yosemite Valley.It is a gray colored rock composed mostly of plagioclase feldspar with lesser amounts of orthoclase feldspar and quartz. The black specks in the rock are biotite mica and hornblende.

As pointed out in the previous posts of this short series on the cliffs of Yosemite Valley, joints are vertical or nearly vertical fractures that can result from stresses on the rock at shallow depths in the crust. Rocks like the Half Dome granodiorite and El Capitan granite are sparsely jointed and stand as bold cliffs that stand out from the valley walls. The Sentinel granodiorite is somewhat more jointed, so it stands more as a tower than a large cliff. It is surrounded by spires and fissures, including the Taft Fissures that can be accessed by trail above the rim of the valley.

Sentinel Rock soars 3,000 feet above the valley floor with an elevation of 7,038 ft (2,165 m). It is a popular climbing challenge. No trails reach the summit, but the Four-Mile Trail to Glacier Point winds across the slopes below. There is a separate peak called Sentinel Dome behind the rim above Sentinel Rock that is a popular hiking destination.

Sentinel stands out in the boldest relief when viewed from Cook Meadow where most everyone stares at Yosemite Falls directly across the canyon. If you are ever lucky enough to visit Yosemite and are standing in awe below the falls, don't forget to look behind you!

There are several other pullouts on the valley loop road that offer good viewpoints, especially with the Merced River in the foreground. If you've been up the Four-Mile Trail or the trail to Yosemite Falls, I'd love to see some of your pictures! I hate to say it, but I've been halfway up the falls trail, snapping pictures right and left, but I didn't get a single shot of Sentinel. Half Dome, yes. Yosemite Falls, upper, middle and lower, yes, selfies, yes, but no Sentinel. It hides in plain sight.

A wonderful rock!

Just a Regular Day on Sentinel Dome

Just a picture today, of an entirely normal day hike up Sentinel Dome on the brink of Yosemite Valley. Well, ok, not an ordinary day. My wife and I got to witness the largest rock fall in Yosemite this year, and then as we made our way down the granite dome, we saw a huge bird (I presume a Redtailed Hawk; I'm open to corrections) perched in a tree at the edge of the cliff. It seemed rather unconcerned about our presence, and I guess was waiting for an unwary chipmunk to come wandering about. I've photographed hawks before, but not from twenty feet away. It was a beautiful creature!

Rock Fall Near El Capitan in Yosemite Today

Your on-the-spot geological reporter was on the scene and on the job today when a rock fall occurred on the cliff just east of El Capitan in Yosemite Valley. Well, ok, I was almost on the scene, and almost on the job...to be honest, I was near the top of Sentinel Dome on the south rim of the valley, eh, dozing on the smooth granite slope. I was listening to what I thought was an odd-sounding jet off in the distance, but when the sounds abruptly stopped, I thought "rockfall!". I ran to the edge of the cliff just in time to see the dust rising from the tumbling boulders.

There has been little in the way of official information as of yet, but it seems to have originated in the vicinity of the cliff at Horse Tail Falls, the high vertical wall just east of the main cliff of El Capitan. I only had time for a cursory examination, but I think the impact point is the white rock on the cliff just above the tips of the trees.

There are white streaks on the dark gray cliffs above the white rock that may be impact scars(click on the photo below for a larger image), and lots of fresh looking boulders on the slope below. I can't tell if trees were snapped off or not. I would appreciate any reports or additional from climbers, hikers, or anyone who was in the meadow below. I will gladly post any pictures, too!

Once a big chunk of rock breaks off a cliff, nearby rocks may be destabilized, and subsequent rock falls are possible. Clearly the climbers know this...

Taking the High Ground: Yosemite as you (maybe) haven't seen it

If the last few entries in the Yosemite series have left you with a fear of cliffs and steep drop-offs, I suggest today a slightly different point of view. Between Taft Point (7,500 ft) and Glacier Point (7,214 feet) stands the barren expanse of Sentinel Dome, which at 8,122 feet is one of the highest easily accessible points on the rim of Yosemite Valley. The normal hike (a bit over a mile) begins at the Taft Point parking area, although anyone who is savvy with a topographic map will note the presence of a service road about 2/3 mile northeast on Glacier Point Road that vastly shortens the hike (maybe a half-mile or less). Unlike the previous viewpoints, the exfoliated dome is set back from the rim, and although there is a short stiff upgrade at the end, there is no place to fall off of. The summit of Sentinel Dome seems to be an outlier of El Capitan granite, although it is surrounded by the granodiorite of Kuna Crest and the Sentinel granodiorite.

The view from the summit of Sentinel is superb, although it reveals little of the valley floor. Instead, it provides a sweeping view of the valley walls and the surrounding region of glaciated peaks, cirques, aretes, domes and cliffs. It stands only 700 feet shorter than Half Dome. It is visible from the classic view of Yosemite Valley, just behind the lowest of the Cathedral Rocks, and just to the right of Sentinel Rock.

Today's picture is looking west towards the portal of the valley, framed by the Cathedral Rocks and El Capitan. The granite that forms both of these edifices is mostly unjointed, and the glaciers that scoured the valley were unable to quarry deeply beneath the cliff faces. The sediment between the portal cliffs is only about 300 feet deep. At the upper end of the valley, in the vicinity of the stables and Stoneman Meadow, the sediments may be as much as 2,000 feet thick!

One may notice the near lack of cliffs beyond the portal formed by El Capitan and Cathedral Rocks. These are the Rockslides, and are composed of diorite of the Rockslides, which is Jurassic-Cretaceous in age, somewhat older than the other rocks in the valley. The rocks have been intruded by mafic dikes and joint more closely than other plutonic rocks in the valley, causing them to easily break down and form talus slopes. Roads built across this slope have been abandoned over the years due to constant rockslide damage.