California Code, Public Resources Code - PRC § 5786.21

(a) A county employee holding a classified civil service position for which eligibility has been established by a competitive examination and certification, and which is similar in grade or class to a district position, shall, at the district's request, be certified by the county civil service commission as being eligible to transfer to and hold that position in the district with the same status and without further examination.

(b) A district employee holding a classified civil service position for which eligibility has been established by a competitive examination and certification, and that is similar in grade or class to a county position, shall, at the county's request, be certified by the county civil service commission as being eligible to transfer to and hold that position in the county with the same status and without further examination.

(c) Any person entitled to participate in promotional examinations for classified civil service positions in either the county or the district shall be entitled to participate in promotional examinations for classified civil service positions for both the county and the district, pursuant to the civil service commission's rules, and to be certified for those positions by the county civil service commission or board of supervisors, and to be appointed to those positions.