I read that some creation myths of American Indians stated they came from "across the ocean". What other creation myths from indigenous people has relevancy to their actual lineage?
Well coastal people often have origin myths that involve deities or origins across the ocean, and mountain people often have origin myths and deities that come from mountains and so on. The problem you have with trying to apply mythology to prehistory is that the sub disciplines study different media. The subject of archaeological enquiry is artifacts and combinations of artifacts (features, sites, site clusters). You just can't use the myths to interpret artifacts. There are connections between folklore and other branches of anthropology but I believe they would be best explored at /r/AskAnthropology.