SCA Proceedings, Volume 23 (2009) Eerkens, Rosenthal, Spero, Stevens, Fitzgerald, and Brink, p. 1 THE SOURCE OF EARLY HORIZON OLIVELLA BEADS: ISOTOPIC EVIDENCE FROM CCO-548 JELMER W. EERKENS DEPARTMENT OF ANTHROPOLOGY, UNIVERSITY OF CALIFORNIA, DAVIS JEFFREY S. ROSENTHAL FAR WESTERN ANTHROPOLOGICAL RESEARCH GROUP, DAVIS, CA HOWARD J. SPERO DEPARTMENT OF GEOLOGY, UNIVERSITY OF CALIFORNIA, DAVIS NATHAN E. STEVENS DEPARTMENT OF ANTHROPOLOGY, UNIVERSITY OF CALIFORNIA, DAVIS RICHARD FITZGERALD CALIFORNIA STATE PARKS, SACRAMENTO, CA LAURA BRINK DEPARTMENT OF ANTHROPOLOGY, UNIVERSITY OF CALIFORNIA, DAVIS Hundreds of thousands of Olivella beads have been found over the last 100 years of archaeological investigation in central California. Strangely, no bead production sites are known from the region. Whether such sites once existed and were destroyed prior to archaeological investigation, or whether bead production was largely decentralized, is unknown. Lacking direct evidence for bead production, this study turns to geochemical information from conveyed beads in an attempt to track their original source. Our multiproxy approach combines measurements of the carbon, oxygen, and strontium isotope ratios in aragonitic shell. Initial data show promise for bead “sourcing” or provenance analysis. We focus on a small sample of beads from a recently excavated Early Horizon (ca. 4000 B.P.) site on Marsh Creek in the California Delta, CA-CCO-548, as a test case. Results suggest production, not on the Pacific Coast, but in a protected bay or estuary with significant influx of freshwater. Beads made out of the purple olive shell, Olivella biplicata, are one of the most commonly formed artifact types found in archaeological sites in California. In some areas, such as San Francisco Bay, they are by far the dominant type of shaped artifact found. Indeed, Olivella beads, made from a variety of species in this genus, are found archaeologically throughout much of North America (Kozuch 2002; Nelson 1991; Thomas 1988). In central California, Olivella beads have received considerable attention from scholars (e.g., Bennyhoff and Hughes 1987; Chagnon 1970; Gifford 1947; Hartzell 1991; Hughes and Bennyhoff 1986; Milliken and Bennyhoff 1993). Much of this research has been directed at seriating different bead forms and using them to identify different temporal units in the archaeological record, an approach that is still commonly used. For example, recent radiocarbon dating of large numbers of beads has shown that these seriations are generally correct, but has led to some restructuring of the basic chronology (Groza 2002; Milliken et al. 2007; Vellanoweth 2001). Chronology-building is clearly an important line of research and forms the backbone of much of our analyses. However, considerable anthropological and environmental information remains to be extracted from Olivella beads. For example, in southern California, scholars have undertaken considerable research on Olivella bead production and spatial distributions (e.g., Arnold 1987, 1991; Arnold and Graesch 2001; Arnold and Munns 1994; Graesch 2004; Erlandson et al. 2005; King 1990;