Cal. Pub. Res. Code § 5159

If these funds at any time exceed the sums necessary for immediate expenditure on the park grounds, or if it is advisable to invest them and make them productive, the park commissioners may invest them or any portion, in interest-bearing bonds of the government of the United States, or the State of California, and the commissioners may use the interest and income. The commissioners may, if necessary, sell and dispose of the bonds.