Archaeological Geology of Upper Pleistocene and Early Holocene Landforms of the Pacific Northwest, USA: Identifying the Colonizer Landscape

While it is generally accepted that the initial Pleistocene human colonizers of the Americas likely entered the continents via the Pacific coast, formal models of their entry and dispersion into the continental interior are scarce. The ability to identify colonizer period archaeological sites for development of such models requires that researchers identify landforms of appropriate age and depositional character to target for large-scale archaeological survey. Well-preserved Upper Pleistocene and Early Holocene landforms are present across the Pacific Northwest. From coastal environs to the Palouse, these landforms represent a remnant landscape which initial colonizers explored at some point subsequent to the last glacial maximum. The types of landforms suitable for deposition and preservation of colonizer period archaeological sites include a broad array of settings, including: Coastal environments, characterized by relict Pleistocene-age landscape features shoreward of the submerged continental shelf; Continental ice-marginal and ice-distal depositional environments, where a variety of glaciomarine and long-standing glacial lakes formed behind the retreating Puget Lobe of western Washington State; Interior Scablands where cataclysmic outburst floods created scoured topographic lows that acted as local depositional basins—often holding paleo-lakes and marshes; and the Palouse loess within the Columbia Basin province, where eolian deposition has buried and preserved the Pleistocene and early Holocene landscape. Along the major drainageways, Upper Pleistocene to Early Holocene alluvial chronologies vary locally, but overall regional trends indicate that climate-controlled aggradation initiated between 12.0 to 11.0KBP, forming distinct terraces in the major river systems and their tributaries. Regional soil formation is evidenced by the Bishop Geosol which dates between 13.5KBP and 11.2KBP, present in a broad variety of depositional environments. Upper Pleistocene archaeology is sparse but present across the region; initial colonizers were broad-spectrum foragers whose toolkit included distinctive stemmed and shouldered bifaces, macroblade tools and crescents.