Showing posts with label Sentinel granodiorite. Show all posts
Showing posts with label Sentinel granodiorite. Show all posts

Sunday, November 11, 2012

How it was Yesterday: Yosemite Jumps From Fall Right Into Winter

Mrs. Geotripper was a bit disappointed two weeks ago when I visited Yosemite Valley and she wasn't able to tag along. So it wasn't too much of a surprise that we ended up making our way to the valley yesterday, looking to take in some of the fall colors.
California may be a leader in many things, but the fall season is not one of them. When most of the deciduous leaves in the nation have long since fallen, our fall colors are just getting started. I saw precious few fall colors two weeks ago in Yosemite Valley, but one could see they would be changing soon.
We weren't disappointed. The oaks and dogwoods where at their brightest shades of yellow and red (and yes, my readers in the eastern U.S., I know our colors can't come close to the colors out your way!). But there was a twist. We arrived on the heels of the first real snowstorm of the season. There were still occasional flurries of snow and pogonip ice coming down as we arrived in the valley.
It was just stunning to me. Yosemite National Park is one of the most beloved of my favorite places in the world, and I go there every chance I get, but in twenty years, I'm not sure I've seen it prettier than this (although I admit I seem to say that with every new season). In the picture above, the oak tree is framed by the lowest of the three Cathedral Rocks (this is the side of the rocks opposite of Bridalveil Fall). The cliff is supported by the El Capitan granite, which lacks jointing (fractures) so it forms vertical cliffs.

In stark contrast to the cliffs of El Capitan granite, the Diorite of the Rockslides is riddled with fractures, and breaks down easily into talus slopes. It lies just west of El Capitan, and is relatively unremarkable unless new snow covers Bridalveil Meadow.
In the picture above, Yosemite Point is almost ignored for much of the year, because the attention of most people is drawn to Yosemite Falls, which normally plummet off the cliff just left of the center of the photo. The cliff is composed of El Capitan granite (102 million years old) and Sentinel granodiorite. The Lost Arrow is a jointed spire just to the left of the point.
Looking at Yosemite Falls, one can also miss one of the other prominent cliffs of Yosemite Valley, Sentinel Rock (above). It's on the south wall of the valley, opposite of Yosemite Falls. It is composed of Sentinel granodiorite, which is about 93 million years old.
Upper Yosemite Falls was not flowing, but enough melting snow collected in the basin below to provide a wispy flow of water to Lower Falls (320 feet).

In the photo above, one can see the cliffs near Taft Point. If you ever need to conquer your fear of heights, you can walk to Taft Point from Glacier Point Road (about a mile) and look straight down for thousands of feet through the Taft Fissures. Needless to say (but I always do anyway), you can't get there right now by road.
The prominent tower in the picture above (on the right side) is one of the Cathedral Spires. I used to get them mixed up; the Cathedral Rocks are just to the west, and are much larger, providing the frame for Bridalveil Falls.
Sentinel Rock looks quite different from another vantage point.

I have no idea if this storm was "it", the final closing down of the high country. If this is another drought year, the snow could all be gone in a few days, and we could be driving over Tioga Pass in January like we did last year. Or, it could be the beginning of the buildup of a nice snowpack that could ease our drought worries here in California. All I know is that it was an indescribably beautiful day (despite my efforts to describe it anyway...).
Next up: the birds of the day, and the sunset...

Monday, April 21, 2008

Under the Volcano: Changing the Emphasis -Part 5

We continue our week's tour of the less famous parts of Yosemite Valley. The Lost Arrow is a fairly familiar sight if you know where to find it, tucked into the cliff just east of Yosemite Falls (see Under the Volcano: Changing the Emphasis -Part 4 ). It is tricky to get some sky behind the rock for pictures, but the clouds cooperated for me in April of 2006. The rock once again is Sentinel granodiorite, and the Lost Arrow is outlined by some prominent vertical joints. As can be seen, the spire is a popular technical climb.

I've not had the pleasure (I'm getting a bit too old and fat to even contemplate this kind of exercise), but if you are wondering what the view is like looking down, check out http://www.100megsfree.com/dew4theq/rock/yosemite/yosemite02.htm.

Thursday, April 17, 2008

Under the Volcano: Changing the Emphasis -Part 2

Once again, I continue a tour of the rocks and other features that sometimes get lost in the shuffle of an iconic view from a famous spot: the Wawona Tunnel View of Yosemite Valley (Standing Underneath Volcanoes). Today, we use a bit of well-placed cloud to blot out Half Dome, and snowy slopes for a backdrop, and suddenly a stunning spire comes into focus: Sentinel Rock. This rock is composed of the Sentinel granodiorite, a coarse-grained, dark-gray, biotite-hornblende granodiorite with abundant sphene that was intruded during the Cretaceous period, about 93 Ma. Another reason that Sentinel Rock receives less attention is that stands across the valley from Yosemite Falls, and many people, entranced by the play of water over the cliffs, never look behind to see this beautiful spire (Yosemite Falls tumbles over a cliff of Sentinel granodiorite as well).

Can you imagine the singular fame of the rock if it were any place in the world besides Yosemite Valley? Tomorrow: one of the lesser known waterfalls....