CA courts are state courts and should not be involved in deciding federal immigration issues.
If general, all US states accept the validity of divorce decrees legally obtained. That is, if the requirements of Guam are met, the decree issued by a court in Guam should be accepted in all US states.
USCIS may question whether a Guam decree is legally obtained if USCIS has reasons to think that it was not. Petitioner of an immigration proceeding generally bear the burden of proving that the petiitioner meets the statutory requirements to the benefit.
You should be prepared to prove that the Guam decree is obtained properly.
You may want to review your specific facts with your attorney to see what legal options you have. There may not be a need to obtain a decree from Guam.
When dealing with US immigration service, it is wise to be candid in all your dealings including obtaining documents to prove and support your case.
It is more time consuming to undo an error than to get it right the first time.
It is advisable to contact an immigration lawyer to discuss your case and find a way forward that will not run you afoul of the system.
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