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I was thinking in terms of Rhyolite in the areas I've been around like Mammoth, which look like they have a lot of larger masses from post explosive eruptiion rewelding.

For good crystals in dikes, I'm going to try to hit the Morgan Pass area again this spring\summer, the peak just northwest of the pass is striped with aplite dikes and in the lower talus debris I picked out some good plates of mica (~2X2 inches) and a little aquamarine in some of the debris. Might be an emerald or two up there!

Just south of the pass is the Pine Creek Tungsten mine, one of, if not the, largest in the world. There's a couple of them up there, if you wanted a really cool resort\TEOTWAWKI site the Strawberry was for sale last I saw. A practically new facility (1980's), subsequently closed when the Chinese began dumping concentrate on the market. It's in scheelite at the metamorphic roof pendant contact.

I've been working with dirt (ahem...soil!) and water for too long!!!

in the lower talus debris I picked out some good plates of mica (~2X2 inches) and a little aquamarine in some of the debris. Might be an emerald or two up there!

The mica book and aqua are excellent signs of gem vugs in pegmatite! Well worth further exploration -- let me know how you do. As for emerald, maybe but I doubt it. Most emerald deposits I know of are metamorphic. The famous Colombian occurrences are in shale IIRC. They've been finding some big ones lately near Hidden, N.C. and I'm not sure about that geology. The entire region is known for emerald, Hiddenite (green spodumene), corundums and gem garnets. They're using ground penetrating radar to locate emerald-bearing vugs.