I can't remember the name, but we have the articles about what could very well have been celts (or picts) crossing the atlantic from possibly spain or Libya, and colonizing the east coast of america sometime after the end of the ice age.
I have surmised in at least one of those posts about the possibility ( logical assumption ) that a sea-faring race that could make it to the east coast would not stop there..
They would follow the coast north, and South, around the florida penensula, along the gulf coast, possibly continue up the Rio Grande, and find themselves well within range of the Pacific coast..
Or, following the coast of Mexico, find one of those narrow stretches of land that would give access by land crossing to the pacific.. ( also creating legends about strange men in boats coming to fullfill prophecy..)
Or, simply moving west from the gulf into california..
The weather was different then, the land probably had sufficient water, and plenty of game..
They had several thousand years without competition from bering straits immigrants... more than enough time..
They would have been there to "greet" the first wave..
Likewise, Pacific immigration is plausible as well, either from Siberia, or from Northern Japan..( Ainu )
Either way, we can surmise they were a sea-faring race..
The "Coracle" is probably very ancient, much older than presently thought.. ( common to Ireland and the British Isles )
My mind wanders.. I will stop now..