Mountaintops with rhyolite mantles of light grey or, more commonly, pinkish to reddish brown are a common sight in Arizona. But this tough volcanic rock is rare in the East. During its formation, vapors were trapped in the viscous rhyolite, creating frothy areas that gradually pit and erode to form weird and grotesque shapes. The rhyolite on Haw Orchard Mountain is bluish gray to purple. The rock was prized by various Indian tribes as a raw material for tools because of its property of making a very sharp edge when flaked.
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