It wasn't a very long time ago that California was red. You don't have to imagine. It was only after Pete Wilson decided to crackdown on latinos that the state shifted into solid D.
Much of the potential 2018 shift in Congress may come from CA, for example: http://thehill.com/homenews/state-watch/369254-perfect-storm...
Eg for the Central Valley districts: "Walters’s district has grown by 33,000 residents, according to U.S. Census Bureau figures. Of those new residents, 30,000 are nonwhite. The white population actually declined in Royce’s district while the overall population grew by 10,000 residents. In Denham’s district, 17,000 of the 21,000 new residents are nonwhite."
(Not to mention the new tax plan was hugely unpopular in CA in general.)
It wasn't a very long time ago that California was red.
Even then, the Legislature was consistently Democrat-controlled (in recent years, Democrat supermajorities).
Without looking it up: when do you think was the most recent time that Republicans controlled both houses of the Legislature?
I looked it up.
The answer?
1970. And that just 1 2-year term and with bare single-seat majorities in both houses.
Before 1969? Next most recent: 1956.