EARLY POSTGLACIAL BIOGEOGRAPHY, SUBMERGED LANDSCAPES AND ARCHAEOLOGICAL POTENTIAL, SAN JUAN ISLANDS AND SOUTHERN VANCOUVER ISLAND, NORTHWEST NORTH AMERICA

Fossil Bison antiquus and other megafauna on the San Juan Islands, Washington, and southern Vancouver Island, British Columbia, document an early postglacial filter dispersal corridor with narrower straits and with lands more extensive than those of today. Isostatic rebound brought relative sea level below modern datum ca. 11,700 ¹⁴C yr BP, reaching or exceeding – 15 m by the earliest Holocene. Exposed areas were later resubmerged by eustatic sea-level rise. Holocene lateral cutting by wave and current action widened water barriers such as Haro Strait. Butchering evidence on an Orcas Island B. antiquus skeleton suggests human presence nearly 12,000 ¹⁴C yr BP. Palynology indicates open pine parkland with localized grasslands before Younger Dryas cooling, suggesting an environment attractive to human groups in quest of large ungulates and other megafauna. Undated lanceolate projectile points may also document such groups. Fossil bone finds on land are mostly in taphonomic windows afforded by wetland environments with calcareous sediments, or aeolian sediments minimally affected by forest soil development. Such windows must exist also in resubmerged lands, so megafaunal bones and artifacts made by Late Pleistocene and Early Holocene hunters are to be expected in dredged or trawled sediments from depths to 15 m, if not more, much as suggested for other locations along the northern Pacific Coast of North America.