California Code, Elections Code - ELEC § 15112

When elections are consolidated pursuant to Division 10 (commencing with Section 10000), and only one form of ballot is used at the consolidated election, the ballots cast by vote by mail voters shall be counted only in connection with elections to which vote by mail voter privileges have been extended by law.

Whenever the period of time within which vote by mail voters' ballots shall be received by the elections official in order to be counted, as provided for any election by this code or any other law of this state, is different from that period of time provided for another election, and the elections are consolidated and only one form of ballot used for both elections, all vote by mail voters' ballots issued for the consolidated election may be counted for both elections if received by the elections official within whichever period of time is longer.