Cal. Elections Code § 2220

(a) The county elections official shall conduct a preelection residency confirmation procedure as provided in this article. This procedure shall be completed by the 90th day immediately before the primary election. The procedure shall be initiated by mailing a nonforwardable postcard to each registered voter of the county preceding the direct primary election. Postcards mailed pursuant to this article shall be sent “Address Correction Requested, Return Postage Guaranteed,” and shall be in substantially the following form: “We are requesting your assistance in correcting the addresses of voters who have moved and have not reregistered. “1. If you still live at the address noted on this postcard, your voter registration will remain in effect and you may disregard this notice. “2. If the person named on this postcard is not at this address, please return this postcard to your mail carrier.” (b) The county elections official, at the county elections official’s discretion, shall not be required to mail a residency confirmation postcard pursuant to subdivision (a) to any of the following: (1) A voter who has voted at an election held within the last six months preceding the start of the confirmation procedure. (2) A voter who has confirmed the voter’s voter registration records on the internet website of the Secretary of State within the last year preceding the start of the confirmation procedure. (3) A person under 18 years of age who has submitted a properly executed affidavit of registration pursuant to subdivision (d) of Section 2102 and who will not be 18 years of age on or before the primary election.