Energy dispersive x-ray fluorescence (EDXRF) analysis of geological obsidian samples from three localities in the
southern Birch Creek drainage revealed that the vast majority of nodules represent the Walcott Tuff, a widespread
toolstone-caliber volcanic glass in eastern Idaho. XRF data generated from analysis of over 500 obsidian artifacts
from four archaeological sites in the Birch Creek Valley document the reliance of prehistoric peoples on Walcott
Tuff obsidian. Data from newly documented Walcott Tuff exposures lead us to conclude that people who frequented
the Birch Creek Valley could have acquired obsidian from proximate Walcott Tuff exposures without having to
travel over 100 km. south to the American Falls area. These results underscore the importance of documenting, and
geochemically analyzing, locations of artifact-quality ash-flow tuff obsidians prior to advancing archaeological
conclusions about obsidian conveyance and population mobility.