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Originally Posted by Dean
Unless I am mistaken, the Sierras are tectonic in origin, not volcanic.
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Yes thats true. The sierras are a result of the Pacific plate and North American plate colliding. There is volcanic activity as mentioned due to previous or currently active hot spots, and well since technically there is magma under everywhere anyway theres bound to be volcanos here or there that manage to seep up through the plates. The pacific rim (ring of fire) which im sure all of us learned about some time in school includes Lassen, Mamoth, etc. and is a result of tectonic activity. Granite, being a Plutonic Igneous rock type is actually directly formed from magma however Granite unlike extrusive volcanic rock, stays under ground for quite some time before reaching the surface.
Oh, I just found this on the usgs website, shows all the recent california activity:
http://earthquake.usgs.gov/recenteqs...-125.-115.html