Obsidian
 

Smokey Bear Flat - Volcanic activity in Mono Basin produced valued and intensely exploited obsidian. Obsidian, or volcanic glass, was the most important tool stone for Native inhabitants. Obsidian can be easily chipped to make an edge exceedingly sharp - sharper than any steel knife. Obsidian from eastern California, in its raw form as big chunks or shaped into bifaces and projectile points (darts, arrowheads), was highly prized and traded by the Paiute and ancestral Native Americans.

The chemical composition of each lava flow is unique, containing different proportions of trace elements, providing a fingerprint of sorts. Through the process of obsidian source analysis (X-Ray fluorescence), each flake or tool of obsidian can be matched to the quarry where it originated, based on the varying amounts of trace elements in the piece. Using this technique, archaeologists have traced obsidian found at prehistoric sites throughout California to quarries in this region. Pieces found great distances from the quarry were transported there via trade.

Another technique, obsidian hydration analysis, can help date artifacts, and thus the sites where they occur. Chipping off flakes, leaving a newly exposed surface shapes obsidian tools. Over time, the once freshly chipped surface hydrates, or absorbs moisture from the environment. The moisture forms a small "hydration band" on the surface. Using obsidian hydration analysis techniques, the thickness of the band is measured with the aid of a microscope. The measured thickness, or reading, of the band translates into a relative age for when the obsidian was last flaked or shaped (a thicker band = older, thinner = younger). Using these two analytical techniques, the archaeologist can determine what quarry a piece of obsidian came from, and when the piece was worked last.