Sunday, October 28, 2012
Up a Creek in Yosemite Valley, and a Wee Mystery For You......
It's not like I was exploring a virgin wilderness, mind you. The picture above was the wide beach in front of the Curry Village canvas tent village. Had this been a summer day, this spot would have resembled a crowd on southern California beach. But today it was deserted; the village is closed down, either for the season or for the hantavirus scare.
A look at a geologic map of the region shows a variety of rocks that formed the same way that granite does (magma cooling slowly deep in the crust), but which have a variety of names based on the proportions of feldspar, quartz and dark iron-bearing minerals like biotite mica: diorite, quartz monzonite, granodiorite, tonalite, and gabbro. The "average" Sierra rock is more like granodiorite than granite. The area upstream of Curry Village is dominated by the Half Dome granodiorite, which at 86-88 million years is one of the younger intrusive rocks of the Sierra Nevada.
What is wrong with the following two images???