California Code, Vehicle Code - VEH § 23113

(a) Any person who drops, dumps, deposits, places, or throws, or causes or permits to be dropped, dumped, deposited, placed, or thrown, upon any highway or street any material described in Section 23112 or in subdivision (d) of Section 23114 shall immediately remove the material or cause the material to be removed.

(b) If the person fails to comply with subdivision (a), the governmental agency responsible for the maintenance of the street or highway on which the material has been deposited may remove the material and collect, by civil action, if necessary, the actual cost of the removal operation in addition to any other damages authorized by law from the person made responsible under subdivision (a).

(c) A member of the Department of the California Highway Patrol may direct a responsible party to remove the aggregate material described in subdivision (d) of Section 23114 from a highway when that material has escaped or been released from a vehicle.

(d) Notwithstanding any other provision of law, a government agency described in subdivision (b), the Department of the California Highway Patrol, or the employees or officers of those agencies, may not be held liable for any damage to material, to cargo, or to personal property caused by a negligent act or omission of the employee or officer when the employee or officer is acting within the scope and purpose of subdivision (b) or (c).  Nothing in this subdivision affects liability for purposes of establishing gross negligence or willful misconduct.  This subdivision applies to the negligent performance of a ministerial act, and does not affect liability under any provision of law, including liability, if any, derived from the failure to preserve evidence in a civil or criminal action.