Obsidian Cliff, also known as 48YE433, was an important source of lithic materials for prehistoric peoples in Yellowstone National Park near Mammoth Hot Springs, Wyoming, United States. The cliff was named by Philetus Norris, the second park superintendent in 1878. It was declared a National Historic Landmark in 1996.
The cliff was formed from thick rhyolite lava flow that occurred about 180,000 years ago. The vertical columns are cooling fractures that formed as the thick lava flow cooled and crystallized. The Cliffs stand at an elevation of nearly 7,400 feet above sea level and go on for about half a mile. The cliffs also extend between 150 and 200 feet above Obsidian Creek. The flow consists of obsidian, a dark volcanic glass. The obsidian is most abundant at the base of the cliff and slowly tapers off to larger concentrations of pumice at the top. Obsidian from this site was first quarried here about 12,000 years ago.