California Code, Elections Code - ELEC § 10261

The city elections official, or a canvassing board appointed by him or her, shall count the votes cast by vote by mail voters. The city elections official or board shall commence this count as soon as the polls close on the day of election, and the count shall continue, for not less than six hours each day providing ballots remain to be counted, until all vote by mail voter ballots have been received within the time provided by law. The result of the vote by mail vote count shall be included with the canvass of returns from the precincts.

The canvassing board, if any, shall be appointed, and the vote by mail vote count shall be conducted in the manner prescribed by Chapter 1 (commencing with Section 15000) of Division 15, insofar as that chapter is not inconsistent with this section.