One of the neat things about my wandering as a geologist is finding the occasional archaeological site. There is an area in Nevada, north of Elko, that has a beautiful welded tuff. It's fairly distinctive, but I have found flakes of it on the flanks of Whistler Mountain, roughly 100 miles away. Really good knapping stone is not all that common, wars were fought over quarries, and it would not be unusual for bifaces and preforms (tools worked down enough to reduce weight and prove the absence of flaws, but not in finished form) to be transported or traded. Finished tools would be at a premium, if well made.
Obsidian is some of the very best material, and the sharpest when flaked right.