Obsidian projectile point conveyance patterns in the lower Humboldt Valley, Nevada

Despite their ubiquity, surface occurrences of obsidian artifacts at archaeological sites throughout western North America have traditionally been viewed as unworthy of serious attention because of the difficulty in dating them. In the past 40 years, the time sensitivity of certain Great Basin projectile point types has been established, which brings the importance of surface collections more center stage. With the coming of age and refinement of geochemical methods, obsidian artifacts from these surface sites can now be analyzed using nondestructive instrumental methods and matched to their geological eruptive origin on the basis of congruence in trace and rare earth element chemistry. Many of these surface assemblages in the Great Basin contain considerable numbers of obsidian projectile points that, when matched to their chemical source of origin, open up entirely new ways to investigate change and continuity in past land use and social relations. The present study was conducted in the lower Humboldt Valley of western Nevada, where large numbers of obsidian projectile points have been collected by professional archaeologists over the past century and housed in academic institutions and museums. In this study, more than 900 obsidian projectile points and bifaces were analyzed from 24 sites and localities within the lower Humboldt Valley using energy-dispersive X-ray fluorescence (EDXRF) to bring data to bear on the question of whether changes in obsidian source use occurred there over the past 5000 years (as determined by time-sensitive projectile points). Significant changes were identified in the direction and distance-to-source of arrow points vs. dart points, and in the source and direction of Humboldt series points and of Humboldt Basal-notched bifaces, which implicate directional shifts through time in social relations among peoples using—and during some periods living at sites in—the lower Humboldt Valley. These results provide independent data to evaluate current views about land use, artifact conveyance, social relations, and technological change in the western Great Basin and beyond.