What do you think makes you a WA resident?
If live and work in CA, you are a CA resident and file a CA resident state tax return.
If for some reason, you do qualify as a WA resident, you file a non-resident CA return and pay tax on your CA income.
Whether you're a CA resident or not for tax purposes isn't up to you; it's determined by California tax law.
Even if you still maintain a home in Washington, California may still consider you a resident for tax purposes. You can read CA's rules on determining residency here: https://www.ftb.ca.gov/forms/2018/18_1031.pdf
Regardless of whether you are a resident or non-resident of CA, CA can tax any income you have from work actually performed within CA.
The difference is that, if you are a CA resident, CA can tax ALL your income. If you are a CA non-resident, CA can only tax income you earn in CA.