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Named stone

Bear Gulch obsidian

Also called Camas Dry Creek obsidian, Camas obsidian, Centennial obsidian, West Camas Creek obsidian, Big Table Mountain obsidian, FMY-90 (the Field Museum's first label)

A kind of obsidian

Bear Gulch obsidianObsidianRockies & Great Basin

Description

Bear Gulch is one of the most used and most widely traded obsidians in the Greater Yellowstone region. The source is a small area of about 28 square kilometers on the Idaho side of the Centennial Mountains, near Kilgore. Its glass comes as angular to rounded pieces 15 to 30 cm across, made of densely sintered black volcanic ash. The broken surface is matte to sub-glassy and even, and it has none of the little crystals or spherulites found in other sources nearby. People used it from about 11,000 years ago. Hopewell burial mounds at Seip, Ohio, and Naples, Illinois, held Bear Gulch obsidian more than 1,500 miles from the source. Researchers first noticed it in Hopewell grave goods, and only later found where it came from.

How to identify it

Colour
Black.
Texture
Matte to sub-glassy, uniform fractured surface; entirely free of spherulites and phenocrysts (Pink 2023).
Inclusions
None: free of spherulites and phenocrysts.

Geology

Obsidian pyroclasts from a small rhyolite dome associated with ring-fracture volcanism at the edge of the Kilgore caldera (Heise eruptive center), still poorly mapped. Deposits are limited to about 28 km2 northeast of West Camas Creek and occur in the stream alluvium. The exact eruptive unit has not been formally described.

Where it comes from

Rockies & Great Basin

States

Quarries and outcrops

  • Bear Gulch / West Camas Creek, Centennial Mountains, near Kilgore, Idaho
  • Obsidian procurement area workshops and quarries (hundreds of sites recorded)

Used by

  • Paleoindian (about 11,000 years ago) and later
  • Hopewell: grave goods at Seip, Ohio, and Naples, Illinois, and in contexts several centuries older (Hughes and Fortier 2007)
  • Wyoming and northern Colorado sites: one of the three most important sources (Smith 1999)

Look-alikes

Stones that are easy to confuse with Bear Gulch obsidian.

  • Obsidian Cliff obsidian (similar chemistry, which is why the Field Museum first guessed a Yellowstone origin)
  • Kelly Canyon rhyolite obsidian (nearby)

Sources

  1. Pink, Jeremias. 2023. The geology, geochemistry, and geographic distribution of southern Idaho obsidian: A provisional context for archaeological provenance research at the INL CRMO. INL/RPT-23-73575, Idaho National Laboratory.inldigitallibrary.inl.gov (opens in a new tab)
  2. Raley, Patrick Martin. 2011. Obsidian Procurement Area Studies: Excavations at Bear Gulch, Idaho. M.A. thesis, California State University, Chico.deschutesmeridian.com (opens in a new tab)
  3. Smith, Craig S. 1999. Obsidian Use in Wyoming and the Concept of Curation. Plains Anthropologist 44(169).archaeologycolorado.org (opens in a new tab)

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