Mark,
The tax people go by what they call "domicile" which is determined by where you vote, have doctors, attend church, have your primary residence (you can own homes in other states), register vehicles, and the like. Every state is different so you have to check the tax rules of each state. Some states also are "tougher" as to what they consider domicile. As long as you continue to "live" in WA and only "visit" in CA, you should not owe taxes to CA - unless you start working there as previously mentioned. When we left CA we told the Registrar of Voters that we were no longer residents, changed to doctors in our new state, changed health care insurance to our new state, changed vehicle registrations to our new state, and everything else we could to make sure we were no longer considered residents.
If you search here in the forum you'll find other threads pertaining to domicle and residency.
ArdraF