January 20, 2020

Geology of the Sierra Nevada

The Sierra Nevada is a huge grantic batholith. It may be "the" classic batholith in the textbooks.

Most of the rock is granodiorite of some sort, although there are plutons that are more felsic (lighter) as well as more mafic (darker). Some plutons are called "quartz monzonite", but these may as well simply be called granite. Other plutons have cute names like "alaskite", which is simply light granite (leucogranite).

Petrologists have been squabbling over names and classifications as long as there have been petrologists. The average citizen may as well, in the light of this uncertainty and confusion, just call the rocks granite and be done with it. Within a given publication, use of names may be consistent and of some use within a limited context.

Owens Valley

Yes, this is strictly speaking the great basin, but coming from the east as I do, I always approach the Sierra by way of Owens Valley, which is fascinating in its own right. The following collection of notes is a wonderful thing:

Yosemite

Maps

It is my intent on my next backpack trip to the Sierra to take a geologic map or maps along in some form and pay attention to different rock units and contacts.

The same maps used in the mosaic above are also available in other forms from the USGS. The following links are my index to the maps. Apparently the USGS once had something called "MapView", but it depends on Adobe Flash, which has almost gone the way of the dinosaur, for better or worse (in this case worse I guess). With the "chrome" browser, you can make the builtin flash work by first changing a setting so it will ask you about every flash site. Then when you visit mapview, be sure to say OK. Then it will try to launch mapview but tell you the flash player is out of date. But there is a button to tell it to go ahead anyway and then you are in business. These links offer the maps in four forms:

Print Optimized PDF (13Mb)
Compressed GeoTiff (25Mb)
Browse Graphic (JPG) (1Mb) - makes a nice "thumbnail" and the text is readable.
Google Earth KMZ (1Mb) - handy to overlay, but no legend.

These are all 15 minute quadrangles (1:62500)


Feedback? Questions? Drop me a line!

Tom's Geology Info / tom@mmto.org