Wednesday, March 9, 2011

Where in the West: Half Dome from Olmsted Point

Yes, it's Half Dome, as Cole Kingsbury of Chaotically Flow-Banded so astutely (and quickly) noted. I figured this month's WITW would be easy, but thought perhaps Half Dome would be overlooked for a while longer, off there in the distance down the upper reaches of the Merced River drainage basin, beyond a hanging valley above Tenaya Canyon. Half Dome is a classic exfoliation dome, one that has been partly cut away along a regional joint system by the glaciations that formed Yosemite Valley. See this excellent picture of the exfoliation of Half Dome at EPOD.

It's a good thing that Ron Schott came up with the location from which the photo was taken — that location being Olmsted Point or, more likely, somewhere near the Olmsted Point pullout on Highway 120, the Tioga Pass Road. I'm sure I would have eventually found the point using Google Earth, but Google Street View just shows fog. Unhelpful.
I don't see a name for the particular side canyon or creek below Olmsted Point, but both the side canyon and main canyon are U-shaped drainages carved by glaciers. The topo map is from MSRMaps, courtesy of the USGS. It's a little messed up as far as the splicing goes, but the north-south dividing line between Sections 31 and 32 is about a mile.

Besides the glacial pavement, glacial polish, glacial striations, and glacial erratics (lower left of the WITW photo) already noted in the comments of WITW: March 2011, there is a nice criss-crossing of joint sets, sets that are roughly orthogonal. One joint set, as seen in my photo, is parallel or sub-parallel to the direction of glacier movement indicated by the striations. Larger, more regional fracture patterns can be seen in the Google Map view above. The regional fracture pattern at N30E is parallel to the hanging valley below Olmsted Point.

Too bad I didn't have my Brunton with me while on this summer, 2000, roadtrip. It mostly wasn't that kind of a trip, more of a family thing with roadtripping and geology added. The particular family involved (mine) has difficulty dissociating roadtripping from geology, and indeed, why should we?!

Roadside Geology of Yosemite Valley by Garry Hayes of Geotripper.
Roadside Geology of Yosemite Valley at Geotripper Images.


Gaelyn said...

Seen from an overlook named after my ancestor.

Silver Fox said...

Very neat, Gaelyn. Here's the history. :)

Silver Fox said...

The Wikipedia entry on Olmsted Point shows a picture nearly identical to the one I took.