Are you in the military?  If so, and if your SLR/HOR is Guam, and you relocated to CA due to military orders, then for state tax purposes you remain a resident of Guam until you officially change your SLR with the military.  If your SLR is Guam, then your active duty military pay is not taxable by CA.

If you're not in the military, and if you literally moved from Guam to CA in 2018 (you abandoned your home in Guam), then you became a resident of CA on the day you began living in your new home in CA.  If that's the case, all your income since then has been and is subject to CA taxation.

Your state of residency for tax purposes is not a matter of "registering"; it is determined by tax law.  This reference gives all CA's rules on determining residency:  https://www.ftb.ca.gov/forms/2019/2019-1031-publication.pdf