Cal. Elec. Code § 13208

(a) In the right-hand margin of each column light vertical lines shall be printed in such a way as to create a voting square after the name of each candidate for partisan office, voter-nominated office, nonpartisan office (except for Justice of the Supreme Court or justice of a court of appeal), or for chairperson of a group of candidates for delegate to a national convention who express no preference for a presidential candidate. In the case of Supreme Court or appellate justices and in the case of measures submitted to the voters, the lines shall be printed so as to create voting squares to the right of the words “Yes” and “No.” The voting squares shall be used by the voters to express their choices as provided for in the instruction to voters.

(b) The standard voting square shall be at least three-eighths of an inch square but may be up to one-half inch square. Voting squares for measures may be as tall as is required by the space occupied by the title and summary.