The Chumash people, who lived both on the mainland and on Santa Rosa island, had a myth, if I remember correctly, that their people had come from somewhere else across a rainbow bridge. Of course I don't believe that there was a literal rainbow bridge, but I interpret it as a cultural subconsciousness of having originally come across the ocean. Their seafaring practices and boat construction were actually fairly advanced in contrast to other tribes on the west coast. If the Polynesians traveled as far through the Pacific as they did, it doesn't seem farfetched that humans could have reached the Americas without crossing the Bearing Strait. Just my hypothesis.