The Pacific Coast Migration Model is a theory concerning the original colonization of the Americas that proposes that people entering the continents followed the Pacific coastline, hunter-gatherer-fishers traveling in boats or along the shoreline and subsisting primarily on marine resources.
The PCM model was first considered in detail by Knut Fladmark, in a 1979 article in American Antiquity which was simply amazing for its time. Fladmark argued against the Ice Free Corridor hypothesis, which proposes people entered North America through a narrow opening between two glacial ice sheets. The Ice Free Corridor was likely to have been blocked, argued Fladmark, and if the corridor was open at all, it would have been unpleasant to live and travel in.
Fladmark proposed instead that a more suitable environment for human occupation and travel would have been possible along the Pacific coast, beginning along the edge of Beringia, and reaching the unglaciated shores of Oregon and California.
Support for the Pacific Coast Migration Model
The main hitch to the PCM model is the paucity of archaeological evidence for a Pacific coastal migration. The reason for that is fairly straightforward--given a rise in sea levels of 50 meters (~165 feet) or more since the Last Glacial Maximum, the coastlines along which the original colonists might have arrived, and the sites they may have left there, are out of present archaeological reach.
However, a growing body of genetic and archaeological evidence does lend support to this theory. For example, evidence for sea-faring in the Pacific Rim region begins in greater Australia, which was colonized by people in water craft at least as long ago as 50,000 years. Maritime foodways were practiced by the Incipient Jomon of the Ryukyu Islands and southern Japan by 15,500 cal BP. Projectile points used by the Jomon were distinctively tanged, some with barbed shoulders: similar points are found throughout the New World. Finally, it is believed that the bottle gourd was domesticated in Asia and introduced into the New World, perhaps by colonizing sailors.
Sanak Island: Redating Deglaciation of the Aleutians
The earliest archaeological sites in the Americas--such as Monte Verde and Quebrada Jaguay--are located in South America and date to ~15,000 years ago. If the Pacific coast corridor was only truly navigable beginning around 15,000 years ago, that suggests that a full-out sprint along the Pacific coast of the Americas had to have occurred for those sites to be occupied so early. But new evidence from the Aleutian Islands suggests the sea coast corridor was opened at least 2,000 years longer ago than previously believed.
In an August 2012 article in Quaternary Science Reviews, Misarti and colleagues report on pollen and climatic data that provide circumstantial evidence supporting the PCM, from Sanak Island in the Aleutian Archipelago. Sanak Island is a small (23x9 kilometers, or ~15x6 miles) dot about the midpoint of the Aleutians extending off Alaska, capped by a single volcano called Sanak Peak. The Aleutians would have been part--the highest part--of the landmass scholars call Beringia, when sea levels were 50 meters lower than they are today.
Archaeological investigations on Sanak have documented more than 120 sites dated within the last 7,000 years--but nothing earlier. Misarti and colleagues placed 22 sediment core samples into the deposits of three lakes on Sanak Island. Using the presence of pollen from Artemisia (sagebrush), Ericaceae (heather), Cyperaceae (sedge), Salix (willow), and Poaceae (grasses), and directly tied to radiocarbon-dated deep lake sediments as an indicator of climate, the researchers found that the island, and surely its now-submerged coastal plains, was free of ice nearly 17,000 cal BP.
Two thousand years seems at least a more reasonable period in which to expect people to move from Beringia southward to the Chilean coast, some 2,000 years (and 10,000 miles) later. That is circumstantial evidence, not unlike a trout in the milk.
Also see the competing and complimentary theories:
for additional hypotheses concerning the population of the Americas.
Balter M. 2012. The Peopling of the Aleutians. Science 335:158-161.
Erlandson JM, and Braje TJ. 2011. From Asia to the Americas by boat? Paleogeography, paleoecology, and stemmed points of the northwest Pacific. Quaternary International 239(1-2):28-37.
Fladmark, K. R. 1979 Routes: Alternate Migration Corridors for Early Man in North America. American Antiquity 44(1):55-69.
Gruhn, Ruth 1994 The Pacific Coast route of initial entry: An overview. In Method and Theory for Investigating the Peopling of the Americas. Robson Bonnichsen and D. G. Steele, eds. Pp. 249-256. Corvallis, Oregon: Oregon State University.
Misarti N, Finney BP, Jordan JW, Maschner HDG, Addison JA, Shapley MD, Krumhardt A, and Beget JE. 2012. Early retreat of the Alaska Peninsula Glacier Complex and the implications for coastal migrations of First Americans. Quaternary Science Reviews 48(0):1-6.