Very interesting Peter, especially -

"Language and technology, specifically in canoe construction, indicate Polynesian impacts on southern California some 1,500 years ago, according to American Antiquity. Terry Jones and Kathryn Klar point out that "three words used to refer to boats, including the distinctive sewn-plank canoe used by Chumashan and Gabrielino speakers, appear to correlate with East Polynesian terms associated with woodworking and canoe construction". These were adopted between AD400 and 800."

Although the Japanese belong to the Tibetan-Mongolian-Korean group of peoples there is also a proto-Malayo-Polynesian element in the Japanese which manifests in both their language and their culture; an example of the latter is the special techniques the Japanese developed in papermaking which I'm convinced have their origin in Polynesian tapa making - tapa is made from the bast fibres of certain plants and was used as both a kind of 'paper' and for articles of clothing.*

* http://www.art-pacific.com/artifacts/nuguinea/barktapa.htm