- Obsidian is found in volcanic areas where the magma is rich in silica and lava has cooled without forming crystals, creating a black glass that can be honed to an exceptionally thin edge.
- Unlike most obsidian, which occurs as small rocks strewn amid other formations, Obsidian Cliff has an exposed vertical thickness of about 98 feet (30 m).
- Obsidian was first quarried from this cliff for toolmaking more than 11,000 years ago.
- It is the United States’ most widely dispersed source of obsidian by hunter-gatherers. It is found along trade routes from western Canada to Ohio.
- It is the United States’ most widely dispersed source of obsidian by hunter-gatherers.
- Obsidian Cliff is the primary source of obsidian in a large concentration of Midwestern sites, including about 90% of obsidian found in Hopewell mortuary sites in the Ohio River Valley (about 1,850–1,750 years ago).
About 90% of the forest on Obsidian Cliff plateau burned in 1988. The fire did not damage the cliff face, but it cleared the surface, creating optimal conditions for archeological surveys. Those surveys added substantially to knowledge about how obsidian was mined from the bedrock and collected as cobbles from the overlying glacial till. Staff are now researching the intensity of use of this obsidian, both within the park and across North America.
The kiosk at Obsidian Cliff, constructed in 1931, was the first wayside exhibit in a US national park. It was listed on the National Register in 1982. The site was designated a National Historic Landmark in 1996.