Assessing the Results of the 2006 and 2007 Investigations at Sunken Village Wet Site

Abstract

The Sunken Village site is situated in a major flood plain basin, at the confluence of the Willamette and Columbia rivers – a geographical position that made it highly attractive as a cross-roads for ancient and current human occupation – known as a trade center supporting large populations for millennia. Major paleoenvironmental events formed the current Portland Basin, including Holocene floods 13–15,000 year ago, scouring the Columbia River channels from massive releases of glacial ice dams in Missoula, Montana, U.S.A., and more recently, a directly upriver release of the massive Bonneville Landslide floods through the Portland Basin region approximately 700 years ago. This last, and no doubt catastrophic event for the ancient Multnomah Peoples, probably sheared and/or buried earlier sites throughout the Portland Basin, and may account for the earliest dates of approximately 700 years BP for the Sunken Village site. The site is located on the Multnomah Channel/Slough which may have once been a main channel of the Willamette River as it flowed northward into the Columbia River, but currently the main Willamette River discharge moves northeastward into the Columbia River, forming Sauvie Island. The Multnomah Channel/Slough forms the west side of the island (see Figures 2.2 and 3.6). As a slough the channel has limited current flow, explaining the fine silt clay matrix of the Sunken Village beach, and its flow is influenced by the tidal action (though it is fresh water at this location). The site is on the outer convex curved edge of the channel point bar, therefore the depositional side, contributing to a slow build up of the original point bar levee at this location (see Figure 2.2). Therefore the beach deposits were progressively accreting out, with organic debris mats being deposited, along with the discarded cultural debris, in vegetal layers along the lee slope of the ancient bar, as revealed in TU4 excavations and deep-cores 5 and 6 at the site (see Punke, above). Two paleoenvironmental conditions no doubt contributed to the ideal conditions at the Sunken Village location for its primary use as an acorn leaching pit station: (a) the non-aggressive currents of this protected slough, forming dense silt/clay point bar deposits for secure construction of hemlock bough-lined pits for the acorn harvest, and, more importantly, (b) the shallow aquifer flow from the island under the natural levee and surfacing along this section of the point bar, creating the underground water flow needed to affectively leach the potentially millions of acorns processed at this prime location. Journal of Wetland Archaeology 9, 2009, 185–201