Cal. Elections Code - ELEC § 9360. Section 9360.
Whenever the elections official is required to mail official matter, as provided in Sections 9312, 9315, and 9317, only one copy of each such official matter shall be mailed to a postal address where two or more registered voters have the same surname and the same postal address.
This section shall only apply if the legislative body of the district adopts this section, and the elections official conducting the election approves of the procedure.