"[Obsidian Cliff] is an imposing escarpment of black volcanic glass, the lower part of which is in the form of great pentagonal columns. The Indians made heads for their arrows and spears from this material, which they found not only vert effective but easy to work. In building the road around the base of the cliff, the obsidian was heated with huge fires and then cold water taken from Beaver Lake was thrown on it. This broke the block of Volcano Glass into pieces that could be conveniently handled."