There used to be an excellent timeline on the web called How the West was Weird, although I can't seem to find it anymore. Essentially, successful Bear Flag revolt in California in 1846, treaty of union with the USA fails primarily due to Douglas' jerking around the treaty in the Senate to mess with Mormons, then there's a Civil War and Reconstruction, and by the time Reconstruction is over, California has been a sovereign nation for 30 years...covering OTL's California, Nevada, Arizona and Baja California, with Deseret also an independent country.