From page 6, California FTB Publication 1032:
"The nonmilitary spouse of a military servicemember who is domiciled in California, but leaves the state with the military spouse on PCS orders outside California, becomes a nonresident upon leaving California. The MSRRA does not alter this result. All income received or earned while a California resident is subject to tax. While a nonresident, only income from California sources is subject to tax."
https://www.ftb.ca.gov/forms/2021/2021-1032-publication.pdf
The income you earn by working in Guam is not "from California sources" and therefore is not subject to California state income tax. Therefore there is no reason for California taxes to be withheld from your pay.
**Answers are correct to the best of my ability but do not constitute tax or legal advice.
