Seasonality of Late Prehistoric Clamming on San Francisco Bay: Oxygen Isotope Analyses of Macoma nasuta Shells from a Stege Mound, CA-CCO-297

Abstract

Using oxygen isotope ratios in terminal growth rings, we estimate the month of harvest of 32 Macoma nasuta shells from a single component Late Phase II (450–200 cal BP) assemblage from CA-CCO-297. Results suggest that clamming occurred throughout the year, but was most pronounced during two pulses in early summer and early winter. We relate the former to longer daylight in early summer that facilitated access to tidal flats and clamming, while the latter may relate more to a lack of other foraging opportunities. We compare the results to Macoma seasonality studies at two other Late Period sites (CA-SFR-171 and CA-SMA-6) and one Middle Period site (CA-ALA-17) on San Francisco Bay. The patterns at all four sites are similar in many regards, but differ in the details and highlight new information on ancient settlement patterns in the region.