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. 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).

Obsidian Cliff was designated as a National Historic Landmark in 1996.