Here is a map of the political divide showing California dividing into two states, not three. Since this was intended for discussion, neither is named California to reduce confusion. Pacifica is the densely populated coastal cities, and Sierra is mostly rural and farming. Pacifica is aimed at liberals and Sierra at conservatives.

https://ibb.co/en6h5w

Sacramento is left in Sierra though currently liberal, but a lot of this would vacate to where ever the Pacifica capital is designated. It would follow the money. San Diego has pockets of liberals, but the large military bases and immigration impact makes most of it conservative.