Sediment Analysis of Two Archaeological Sites in the Deception Pass Area, Fidalgo Island, Washington: A Geoarchaeological Approach

The Western Washington University’s Field School (1999 and 2000 seasons) excavated two prehistoric shell midden sites located on Lighthouse Point in the Deception Pass area, Washington. A geoarchaeological approach was taken in studying site depositional processes; grain size analysis and study of sedimentary structures present in excavation profiles provided information about both natural and cultural deposition at site SK-144 and SK-46. Grain size analysis shows that angular, unconsolidated and poorly sorted colluvial sediments compose the lower beds of SK-46. While it is thought that colluvial sediments also underlie SK-144, difficulty relocating where samples were taken from makes testing this impossible. Regressing beach berms evident in excavation profiles of SK-144 show that changing sea level most likely altered the sedimentation rate and tombolo formation at SK-144; the surface area of the tombolo and therefore the site was larger in the past than it is today. A recent rise in local sea level and possible subsidence of the tombolo has caused erosion of the site evident today.