California Elections Code Section 13

(a) No person shall be considered a legally qualified candidate for any office or party nomination for a partisan office under the laws of this state unless that person has filed a declaration of candidacy or statement of write-in candidacy with the proper official for the particular election or primary, or is entitled to have his or her name placed on a general election ballot by reason of having been nominated at a primary election, or having been selected to fill a vacancy on the general election ballot as provided in Section 8806, or having been selected as an independent candidate pursuant to Section 8304. (b) Nothing in this section shall be construed as preventing or prohibiting any qualified voter of this state from casting a ballot for any person by writing the name of that person on the ballot, or from having that ballot counted or tabulated, nor shall any provision of this section be construed as preventing or prohibiting any person from standing or campaigning for any elective office by means of a write-in campaign. However, nothing in this section shall be construed as an exception to the requirements of Section 15341. (c) It is the intent of the Legislature, in enacting this section, to enable the Federal Communications Commission to determine who is a legally qualified candidate in this state for the purposes of administering Section 315 of Title 47 of the United States Code.