Implications of a freshwater radiocarbon reservoir correction for the timing of late Holocene settlement of the Elk Hills, Kern County, California

Uncertainties regarding the magnitude of freshwater radiocarbon reservoir effects can introduce random errors into dates on archaeological freshwater carbonates. As a result, many archaeologists avoid dating freshwater shells unless no other datable materials are available. The chronology of prehistoric occupation of the former Naval Petroleum Reserve No. 1 (NPR-1) at Elk Hills, Kern County, has been established with 50 radiocarbon dates on freshwater mussels (Gonidea and Anodonta sp.). Characterization of any freshwater radiocarbon reservoir effect is crucial for the accurate interpretation of inferred settlement and subsistence changes on the Elk Hills. Paired charcoal and freshwater mussels sampled from closely associated contexts were dated to identify a freshwater reservoir effect. Paired Anodonta and Gonidea sp. shells were dated to investigate interspecific differences in fractionation. Results indicate that a 340 ± 20 ¹⁴C yr correction should be applied to conventional ¹⁴C dates on freshwater carbonates in the Buena Vista Basin before calendar calibration. Evidence of interspecific differences is inconclusive. Dates recalibrated with the reservoir correction indicate that widespread occupation of the Elk Hills is correlated with increasing precipitation towards the end of the Medieval Climatic Anomaly and during the Little Ice Age, suggesting that slough resource exploitation may have been driven by regional population pressure rather than drought-related declines in aquatic productivity.