Being California-born, i can't help but have a little curiousity about who and what dwells amongst the rainforests and beaches of the west coast of Northern Crown, as well as a few ideas of what it might be like.
I'm guessing the presence of Fou Sang will prove a stumbling block in the formation of an equivalent to Alta California, unless it lies sufficiently north. If that's so, then Espaniard explorers have likely already made some inroads by the time the campaign setting is placed. If these Espaniards follow a similar route to their real world fellows, then they'll miss San Francisco Bay entirely for about a century- perhaps this is where Fou Sang is situated.
The culture of Fou Sang is probably a mix of Cathayan and First Ones culture. The natives which were described in real-world accounts of this legendary nation were said to have picked up elements of Buddhism from missionaries who journeyed centuries ago from what is now Afghanistan, and to have been ruled by "An emperor, or a main chief, with the help of several officials". The arrival of the Cathayan emperor, his family, and servants may have been marked by a show of wealth and power which led to the local government being itself overthrown, at least in part.
I can imagine this as a nation ruled by a Cathayan aristocracy, with a few First Ones or mixed parentage officials placed mainly to keep their fellow citizens from objecting too strongly to foreign rule. The emperor is wary of any threats to his already greatly diminished power, and fiercely protects those resources and riches he managed to escape with. His palace, formerly a single large village which was fortified and decorated to reflect more Cathayan sensibilities, is fiercely guarded; his citizens are taught to distrust non-citizens, who are painted as savage thieves who would love nothing more than to steal away the splendorous paradise his imperial majesty has created.
It may very well be that California is-- at least, in part --an island in the world of Northern Crown, as was believed by many real world scholars in the 17th century. If this is so, perhaps there is an amazonian nation, as described in The Exploits of Esplandian. Ruled by a queen of great beauty and height, this place seems in both appearance and customs a displaced Nyamban nation.
Yet another possible nation comes from the suggested etymology of "California" as being derived from "caliph". Perhaps a Nasrid presence has been established here, Granadan colonists arriving before Espaniards, possibly fleeing the growing strength of EspaÃ±a. This colony has grown to encompass several pre-existing nations, with the citizenry being converted to Islam where possible, and has been declared a new Caliphate.
Of course, this only covers California- there are abundant myths, legends, and odd history of other west coast states and regions, and if i had more time today i'd come up with something for a few of these, too. I'd love to see other people's ideas on this, no matter how small.