Obsidian Cliff is a vertical cliff, 150 - 200 feet high, rising above a marshy area containing a small lake formed by a beaver dam. The cliff lies about halfway between Norris Junction and Mammouth Hot Springs. While it is not known exactly what conditions are required for obsidian, a volcanic glass, to form in rapidly cooling lava, it has formed at several locations within Yellowstone. At Obsidian Cliff, the concentration of obsidian is greatest at the base of the cliff while farther toward the top of the cliff weathered pumice is found.
Obsidian was a highly valued trade commodity among the native peoples of North America for many centuries. It is easily shaped and forms sharp edges. It was used for cutting tools, projectile points and decorative items. Its use for decoration was due to its luster and its variation in color from jet black through yellowish brown, purplish brown and olive green.
That the obsidian from Yellowstone was widely traded has been established by analyses that place the source of the obsidian found in the Hopewell Mounds (east of the Mississippi River) as the Yellowstone lava beds. Before the "discovery" by Columbus and the arrival of the Spanish, which disrupted trade routes, Yellowstone obsidian was traded as far as Mexico and Guatamala.