California, like many states in the U.S., has legalized marijuana. The use and sale of marijuana under Federal Law, however, remains illegal. Immigration is governed by Federal Law. As such, possessing, using or selling marijuana can make a noncitizen of the U.S. inadmissible, deportable, or ineligible for Naturalization.
It has been reported that in some jurisdictions, immigration officers at USCIS field offices are beginning to ask specific and detailed questions regarding marijuana. If an applicant admits to use of marijuana this can lead to the USCIS Officer obtaining a sworn statement from the Applicant during the interview in regards to marijuana use. The statement is then used as a basis to deny the applicant for the benefit he or she seeks as it can be used to support inadmissibility charges. Remember, even if the Applicant has no convictions relating to marijuana use, a sworn statement admitting to possession or use of marijuana, can be used to support inadmissibility charges and the like.
This something that needs to be prepped for and non citizens need to be aware of when applying for an immigration benefit.