Oregon Water Science Center Studies

Geomorphic Context of Archeological Sites near Ridgefield, Washington (OR 179)

PROJECT CHIEF: James E. O'Connor

LOCATION: Lower Columbia River near Ridgefield, Washington

BACKGROUND

Several key Chinook archeologic sites are located on flood plains along the lower Columbia River in northestern Oregon and southwestern Washington. The Cathlapotle site near Ridgefield, Washington, has been subject to intensive excavation and investigation during the last several years.

Sites seem to be preferentially located along side channels where there was access to the main-stem Columbia River. Additionally, the chronology of sites such as the Cathlapotle site are thought to be affected by the sequence of large Columbia River floods. The February 1996 flood on the Columbia River caused extensive bank erosion along the lower Columbia River, exposing additional archeological sites as well as producing clean exposures of late Holocene alluvial stratigraphy.

OBJECTIVES

1. Describe the stratigraphic and geomorphic context of archeologic sites on the Columbia River floodplain near Ridgefield, Washington.

2. From examination of alluvial stratigraphy, determine the late Holocene history of large floods on the lower Columbia River.

APPROACHES

1. Reconnaissance-level field, map, and aerial photograph examination of stratigraphy and geomorphology of the Columbia River floodplain near Ridgefield, Washington will be used to broadly evaluate overall geomorphic and stratigraphic context of known archeologic sites.

2. Detailed stratigraphic analysis, including sedimentology and radiocarbon dating to two stratigraphic sections near Ridgefield will allow detailed reconstruction of local Columbia River flood history.