Cal. Elections Code - ELEC § 9290. Section 9290.
Whenever the elections official is required to mail official matter, as provided in Sections 9223, 9280, 9281, 9282, and 9285, only one copy of each piece of 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 city adopts this section and the election official conducting the election approves of the procedure.