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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. 

Forty years ago, Knut Fladmark (1979) argued that the Pacific Coast offered a viable alternative to the ice-free corridor model for the initial peopling of the Americas—one of the first to support a “coastal migration theory” that remained marginal for decades. Today, the pre-Clovis occupation at the Monte Verde site is widely accepted, several other pre-Clovis sites are well documented, investigations of terminal Pleistocene subaerial and submerged Pacific Coast landscapes have increased, and multiple lines of evidence are helping decode the nature of early human dispersals into the Americas. Misconceptions remain, however, about the state of knowledge, productivity, and deglaciation chronology of Pleistocene coastlines and possible technological connections around the Pacific Rim. We review current evidence for several significant clusters of early Pacific Coast archaeological sites in North and South America that include sites as old or older than Clovis. We argue that stemmed points, foliate points, and crescents (lunates) found around the Pacific Rim may corroborate genomic studies that support an early Pacific Coast dispersal route into the Americas. Still, much remains to be learned about the Pleistocene colonization of the Americas, and multiple working hypotheses are warranted.