California Code, Education Code - EDC § 35034

(a) Where the entire area of a county is included within one unified school district or where the entire area of a county is included within one unified school district except for the portions of the county that are included in a school district that is under the jurisdiction of the county superintendent of schools of another county, the county superintendent of schools may be employed as the superintendent of schools of the unified school district;  provided he or she is the holder of a certification document authorizing him or her to perform those services.  If a county superintendent of schools is employed as the superintendent of schools of a unified school district, he or she may be paid the salary, in addition to that provided by law for his office of county superintendent of schools, that he or she and the governing board of the unified school district may agree upon.

(b) Any county superintendent of schools who was employed as a district superintendent of a unified school district on or before September 20, 1963, may continue to perform those services without possessing the certification document otherwise required so long as he or she remains continuously employed or reemployed in his or her position.

(c) Where the entire area of a county is included within one unified school district except for the portions of the county that are included in a school district that is under the jurisdiction of the county superintendent of schools of another county, the person who was county superintendent of schools at the time the unified school district was formed may be employed as the superintendent of schools of the unified school district without possessing the certification document otherwise required so long as he or she remains continuously employed or reemployed in his or her position.