Cal. Rev. & Tax. Code § 1626

The board of supervisors of any county which has created one or more assessment appeals boards may discontinue all of said boards effective on the first Monday in September, subject to any such board continuing to function until matters pending before it have been disposed of. If all of such boards have been discontinued, no new board or boards may be created to function prior to the next succeeding first Monday in September. Notwithstanding the foregoing, the board of supervisors of any such county may increase, or may decrease to not less than one, the number of such boards, effective from and after the next succeeding first Monday in September, provided that any board so discontinued shall continue to function until matters pending before it have been disposed of.