ArrowPoint

Named stone

Mount Taylor obsidian

Also called Grants Ridge obsidian, Horace Mesa / La Jara Mesa obsidian, Mount Taylor Volcanic Field obsidian

A kind of obsidian

Mount Taylor obsidianObsidianTexas & Southwest

Description

Mount Taylor obsidian comes from the Grants Ridge rhyolite in the Mount Taylor Volcanic Field of west-central New Mexico. Two flavours matter to artifact people. East Grants Ridge glass is somewhat vitrophyric, meaning it has crystals, and is only an adequate toolstone, though formal tools including points were made of it. Horace and La Jara Mesa glass is aphyric, with nodules up to 8.5 cm, and was the better medium that Zuni and Hopi-area knappers preferred. The mesa deposits date to about 3.3 million years. Nodules also wash into the Rio Salado. Mount Taylor glass appears in Clovis assemblages: a point at Mockingbird Gap and all three flakes excavated there came from Mount Taylor, about 180 km away.

How to identify it

Texture
East Grants Ridge: somewhat vitrophyric (with crystals), adequate for tools. Horace and La Jara Mesa: aphyric, nodules up to 8.5 cm, a better medium (Shackley).
Inclusions
Crystals (vitrophyric fabric) at East Grants Ridge.

Geology

Grants Ridge rhyolite of the Mount Taylor Volcanic Field (late Tertiary). The Horace and La Jara Mesa ash flow (ignimbrite) dates to 3.26 million years by argon dating; East Grants Ridge glass was dated at 3.34 million years by an older potassium-argon method. The mesas are separated by a normal fault, but the two are one ash flow and one magma source.

Where it comes from

Texas & Southwest

States

Quarries and outcrops

  • East Grants Ridge, Mount Taylor Volcanic Field
  • Horace Mesa and La Jara Mesa (aphyric nodules)
  • Rio Salado alluvium (secondary nodules)

Used by

  • Clovis: Mount Taylor obsidian in the Mockingbird Gap surface collection and in all three excavated flakes (Hamilton and others 2009)
  • Cody complex: two Grants Ridge artifacts in the sourced set (Dolan and others)
  • Zuni and Hopi areas: archaeological obsidian preferred the aphyric glass (Shackley)

Look-alikes

Stones that are easy to confuse with Mount Taylor obsidian.

  • Cow Canyon (Arizona) and Jemez obsidians (other Clovis-era sources in the region)

Sources

  1. Shackley, M. Steven. Geoarchaeological XRF Laboratory, University of California, Berkeley. Southwestern obsidian source description: Grants Ridge and Horace/La Jara Mesa, Mount Taylor Volcanic Field.swxrflab.net (opens in a new tab)
  2. Hamilton, Marcus J., Bruce B. Huckell, and M. Steven Shackley. 2009. Clovis Obsidian Sources in the Central Rio Grande Rift Region of New Mexico. Current Research in the Pleistocene 26:62-65.unm.edu (opens in a new tab)
  3. Dolan, Sean G., Judy Berryman, and M. Steven Shackley. 2016. The Source Provenance of an Obsidian Eden Point from Sierra County, New Mexico. PaleoAmerica (accepted manuscript, Los Alamos National Laboratory LA-UR-15-28702). https://doi.org/10.1080/20555563.2016.1138822osti.gov (opens in a new tab)

Points made from this stone

All materials