Cal. Pub. Util. Code § 102100.10

Each voting entity appointing members to the board in accordance with Section 102100.2 may also select, in the same manner as the primary member or members, one or more alternates, as the case may be, to serve on the board when the primary member or members are not available. Each alternate shall be appointed to serve for a specific member. The alternate shall be subject to the same restrictions and shall have the same powers, when serving on the board, as the primary member. The legislative body of any voting entity appointing an alternate shall provide written notification to the secretary of the board of each appointment of an alternate in order for the appointment to be effective.