HOLOCENE-AGED LOESS DEPOSITS IN THE UPLANDS OF THE PORTLAND BASIN

Two archaeological sites discovered near Battle Ground, Washington, challenge the accepted view of the depositional history of the Portland Basin since the late Pleistocene. The Gee Creek sites are located in the uplands of the Columbia River Basin near Portland, Oregon, at an elevation of 76 meters above mean sea level. Intact archaeological deposits dating to as early as 8,000 years ago were found buried under nearly one meter of wind-deposited sediment that blankets the hills surrounding the sites. The archaeological and stratigraphic records at the sites suggest that sediment accumulation in upland areas of the region did not cease after the deposition of alluvial sediment during the catastrophic, late Pleistocene Missoula Floods. Rather, deposition continued in periodic episodes through the Holocene. Periods of decreased eolian accumulation and relative landscape stability are recorded in the form of archaeological deposits that indicate human occupation of the landscape. These eolian deposits appear to be loessal in origin and closely resemble the Portland Hills Silt loess deposits that are geologically mapped in many of the upland areas within the Portland Basin.