California Code, Government Code - GOV § 31680

(a) A member retired for service or disability shall not be paid for any service rendered by him or her to the county or district after the date of his or her retirement, except:

(b) As herein used the term “services rendered” shall refer to service rendered as an officer or employee of the county or district and shall not refer to services performed by a retired officer or employee as an independent contractor engaged by a county or district under a bona fide contract for services within the purview of Section 31000 of this code.

(c) Beginning January 1, 2013, if any provision of this section conflicts with the California Public Employees' Pension Reform Act of 2013, the provisions of that act shall prevail.