The existing California, entirely ruled by Democrats, has effectively already seceded, denying the federal government's authority over immigration, air quality, water rights, energy, drugs, food processing, "fair" housing, and countless other matters. They'd be much happier on their own, and God knows the country would be far better off without them. Let's wave them a fond adieu.
We can sweeten the deal by giving them eastern Oregon and Seattle, too. We'd want a great big, beautiful wall between the two countries, of course.