Obsidian Source Use in the Greater Yellowstone Area, Wyoming Basin, and Central Rocky Mountains

Using x-ray fluorescence (XRF) analysis from nearly 2,300 sourced obsidian artifacts in western Wyoming, southwestern Montana, and eastern Idaho, we demonstrate regional diachronic changes in access to and preference for particular obsidian sources throughout the West. We focus on both (I) long-term patterns of obsidian use that may inform us about the timing of precontact migrations of Numic (Shoshone) speakers into the Rocky Mountains and (2) the extent to which later contact among Native inhabitants and European immigrants was a mechanism for reducing elements of precontact mobility and exchange in the postcontact era. We view indigenous responses to contact in the study area as an active, strategic process with measurable material consequences. Despite a well-documented increase in mobility among local Native groups as a result of the introduction of the horse, our study demonstrates a restriction and reduction in Historic period source use in western Wyoming. We propose that changes in obsidian source use are a reflection of ethnogenesis and development of ethnographic bands as a response to culture contact among indigenous inhabitants and with Europeans.