California Code, Government Code - GOV § 19993.1

State-owned motor vehicles shall be used only in the conduct of state business.  State business shall include the operation of state-owned vehicles as commute vehicles in a carpool or vanpool program authorized by a state agency, provided that a daily, weekly, or monthly fee is charged that is adequate to reimburse the state for the cost of providing such vehicles for such purpose.  No state officer or employee shall use, or permit the use of, any state-owned motor vehicle other than in the conduct of state business.