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The presence of well-documented sites in the Americas predating and south of the opening of an ice-free corridor in the North American ice sheets lends credence to a Pacific coastal migration theory (CMT) explaining the route for the initial peopling of the Americas. This theory has been informally discussed for more than 50 years, but until recently, has been largely ignored and never properly defined as a result. We provide a formal definition of the CMT which, briefly stated, is that Upper Paleolithic populations moved from Asia to coastal regions along the northwestern Pacific Rim between ~45-30 ka. By ~30 ka these coastal populations developed a mixed maritime, nearshore, and terrestrial adaptation involving the use of boats, shell fishhooks for deep-water fishing, and a stemmed point and macroblade core technology. About 25-24 ka a subset of these coastal populations became isolated somewhere in the vicinity of the Japan/Paleo-Hokkaido, Sahkalin, Kuril (PSHK) region, developing genetically into the ancient Native American (ANA) populations that eventually settled the Americas. Between ~22-16 ka these ANA people began migrating by foot and boat along the southern Beringian coast and down the Alaskan and Canadian coastline into the Americas south of the continental ice sheets before eventually expanding inland. We develop a series of testable hypotheses through which the CMT can be examined. 

Radiocarbon dating of the earliest occupational phases at the Cooper’s Ferry site in western Idaho indicates that people repeatedly occupied the Columbia River basin, starting between 16,560 and 15,280 calibrated years before the present (cal yr B.P.). Artifacts from these early occupations indicate the use of unfluted stemmed projectile point technologies before the appearance of the Clovis Paleoindian tradition and support early cultural connections with northeastern Asian Upper Paleolithic archaeological traditions. The Cooper’s Ferry site was initially occupied during a time that predates the opening of an ice-free corridor (≤14,800 cal yr B.P.), which supports the hypothesis that initial human migration into the Americas occurred via a Pacific coastal route.