Geology of National Parks, 3D and Photographic Tours
Obsidian Cliff is located about six miles north of Norris Geyser Basin along Highway 89 to Mammoth Hot Springs. Because it can be chipped into very sharp edges, obsidian is an excellent rock for making stone tools and arrowheads. Obsidian Cliff was an important prehistoric source of obsidian for indigenous tribes of the Midwest and Great Plains. Note the columnar jointing of the two different lava flows preserved in the cliff. The lower obsidian-bearing cliff is an early Quaternary lava flow (called the Obsidian Creek Member of the Plateau Rhyolite). The upper unit in the cliff is the Roaring Mountain Member (Christiansen and Blank, 1972).
Obsidian forms from rapidly cooling lava that has a very low volatile content (i.e. water, carbon dioxide, etc).