You could keep tracing back to a few earlier generations until you come up with evidence and you may want to also do some DNA testing to go much further back.
My understanding is that in going back thousands of years, that American Indians and Europeans had a common ancestor in Asia. Some descendants went East and eventually into what is now Alaska and others went West into Europe.
I don't know about mtDNA, but my Y-DNA, R1b shares a lot of elements that are also found in native Americans.
You may want to check out "Deep Ancestry" ...DNA Quest to Decipher Our Distant Past, by Spencer Wells. Pages 99-100 and other sections of the book could be worth reading.