Cal. Elections Code § 2105.7

(a) A state or local juvenile detention facility, including, but not limited to, a juvenile hall, juvenile ranch, juvenile camp, or a facility of the Department of Corrections and Rehabilitation, Division of Juvenile Justice, shall do all of the following: (1) Identify each individual housed in the facility who is of age to register to vote and not in prison for the conviction of a felony. (2) Provide an affidavit of registration to each individual housed in the facility who is of age to register to vote and not in prison for the conviction of a felony by doing either of the following: (A) Providing the individual a paper affidavit of registration. (B) Directing the individual to an affidavit of registration provided on the internet website of the Secretary of State. (3) Assist each individual housed in the facility who is of age to register to vote and not in prison for the conviction of a felony with the completion of the affidavit of registration, unless the individual declines assistance. (b) A facility providing paper affidavits of registration pursuant to subdivision (a) shall do either of the following: (1) Assist the individual who completed the voter registration card in returning the completed card to the county elections official. (2) Accept any completed voter registration card and transmit the card to the county elections official.