California Code, Government Code - GOV § 16470

The Pooled Money Investment Board shall, at such times as it deems necessary, determine whether any portion of the money then on deposit in the State Treasury to the credit of any fund, exclusive of the General Fund, is not necessary for immediate use; and if so, it shall determine the amount thereof in each such fund, which amount shall thereupon be designated as “surplus money.” This article does not apply to any fund included within subdivisions (b), (c), (d), (e), and (f) of Section 16475, or the State Highway Fund, the Public Employees' Retirement Fund, Legislators' Retirement Fund and State Teachers' Retirement Fund, or the Unemployment Compensation Disability Fund.

Any special fund excepted from this article may elect, by filing with the Pooled Money Investment Board a notice of election, to come under the provisions of the Surplus Money Investment Fund; which election shall be revocable by such special fund effective as of December 31st or June 30th of any year upon 30 or more days' notice prior to either of said dates.