Cal. Gov. Code § 31983

In any county in which the predecessor of this chapter has become operative prior to August 4, 1943, the persons employed in positions included in the definition of “county peace officers” by subdivision (b) of Section 31904 shall become members of the system on the first day of the calendar month following the expiration of 30 days after the board of supervisors has adopted by a four-fifths (4/5) vote a resolution providing for the inclusion of such positions in the system. Thereafter each person employed in any position included in that definition shall become a member on the first day of the calendar month following the expiration of 30 days after he is so employed.