Well, I lived there for 6 months and could only find Rhyolite. There is flint in the mountains but, the lens are very small and the surrounding limestone is very dense and thick. I was there doing archaeological fieldwork and most of the artifacts we found were "exotic" materials... so if the old guys brought in rock... there's nothing worth while there.
Also, watch out for the dang mesquite thorns!
Later,
Michael