Big Sites—Short Time: Accumulation Rates in Archaeological Sites

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Large, complex archaeological sites are often characterized by only a handful of radiocarbon dates. This practice encourages indiscriminant dating of sites for the sole purpose of determining age. If a more rigorous dating scheme is employed and accumulation rates are calculated, otherwise invisible aspects of human behaviour become apparent. Issues central to settlement pattern analysis, such as abandonment and reoccupation events, population fluctuations, building activities, and activity areas are more easily identified when accumulation rates are calculated. In this study, accumulation rates are calculated for seven shell midden sites found in the San Juan Islands, Washington. The collections are stored at the Burke Museum of Natural History and Culture, University of Washington, Seattle, Washington. Eighty-two charcoal pieces were selected according to a comprehensive horizontal and vertical sampling regime and radiometrically dated. Accumulation rate calculations suggest that large archaeological sites, like these shell middens, do not always represent continuous human occupation characterized by gradual accumulation of material. Rather, these large complex sites accumulated during short-duration occupations that were repeated infrequently in the same area. This research recommends that numerical accumulation rates be calculated using at least two calculations; the excavation unit accumulation rate and the entire site accumulation rate, and that the excavation unit accumulation rate is the more useful scale for interpreting settlement history. Calculations of these rates focus the multifaceted interaction between human behaviour and natural processes in a way that qualitative guesses cannot.