Cal. Gov. Code § 31800.5
Whenever pursuant to the provisions of this article federal old age and survivors insurance provisions of the Social Security Act have been integrated as to members employed by a county or district, the relationship may be converted to a supplementation system under which the social security benefits shall be in addition to unintegrated retirement benefits. The conversion shall take place when the governing body of the county or district adopts by majority vote, a resolution providing that the conversion shall take place; provided, however, the resolution shall have received prior approval by majority affirmative vote of eligible members employed by the county or district in a referendum conducted in accordance with the provisions of Article 2 (commencing with Section 22300), Chapter 2, Part 4, Division 5 of Title 2 of this code. The conversion shall take place and become fully effective and operative on the date specified in the resolution.
In the event that the employees of the county or district are divided into more than one coverage group for purposes of the Social Security Act, the conversion may be with respect to all coverage groups or one or more coverage groups as the governing board may determine in the resolution.
Ca. Gov. Code § 31800.5