Cal. Elec. Code § 2120

If the county elections official receives a letter from a voter stating that the voter has moved to a new address in another county in the state, the elections official shall immediately notify the elections official of the county to which the voter has moved. Upon receipt of the notice, the elections official of the county to which the voter has moved shall send to the voter a voter registration card, and shall instruct the voter that in order to record a change of address, the voter must reregister on a new affidavit of registration. The elections official shall cancel the old registration for any election occurring at least 29 days after the receipt of the letter.