Section 31500 Of Article 2. Establishment Of System From California Government Code >> Division 4. >> Title 3. >> Part 3. >> Chapter 3. >> Article 2.

. A retirement system is established in any county for eligible officers and employees by the adoption of an ordinance, accepting this chapter, by:
  (a) A majority vote of the electors voting on the proposition at a special or general election; or
  (b) A four-fifths vote of the board of supervisors.