Cal. Gov. Code § 31559

Whenever a county or district subject to the provisions of this chapter takes over and assumes any of the functions of any other public agency, and because of such assumption all or any employees of such other public agency become employees of such county or district, any such employee whose principal duties consist of active law enforcement or active fire suppression, as defined in Sections 31469.3, 31470.2 and 31470.4, who, because of such transfer of functions, is employed in such a position in such county or district, shall become a safety member on the first day of the calendar month following his entrance into service.