I just want to say that I have identified the stone. "Rhyolite" This pink Rhyolite {high grade} is high in silica which makes knapping possible. It is a volcanic stone. If you look carefully you can see holes where gas has escaped. These holes are known as "Vugs" I am sure you needed to know that.
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http://www.thudscave.com/petroglyphs/knappable.htm