California Code, Public Utilities Code - PUC § 130053.5

(a) The Riverside County Board of Supervisors shall establish a procedure by which a member of that board may appoint an alternate member of the board of supervisors to represent the member for one meeting of the Riverside County Transportation Commission.  Notice of the alternate appointment shall be made in writing to the clerk of the commission 24 hours prior to the meeting.

(b) Each incorporated city in Riverside County shall appoint one alternate member to the commission who shall represent the regular member of the commission who serves on behalf of the city, if the regular member is not in attendance at a meeting.  Notice of the alternate appointment shall be made in writing to the clerk of the commission 24 hours prior to the meeting.  If an incorporated city appoints an alternate member, the alternate member shall be either the mayor or a city council member of that incorporated city.