Cal. Elections Code - ELEC § 9180. Section 9180.
Whenever the county elections official is required to mail official matter, as provided in Sections 9119, 9120, 9160, 9162, and 9167, only one copy of each 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 board of supervisors adopts this section.