Cal. Public Contract Code § 20419

If any local, state or national agency or authority contributes the labor, or labor and any portion of the materials, supplies or equipment necessary for the construction of any improvement authorized under this division, the contract shall be for only those items which are not contributed by any such agency or authority. If proposals or bids are invited only for the furnishing of materials, supplies and equipment or any portion thereof not furnished by such agency or authority, the notice shall contain a statement to the effect that the legislative body may cancel the order for any undelivered materials, supplies or equipment by giving the successful bidder 24 hours notice of the cancellation, in which event the successful bidder will be entitled to compensation for only so much of the material, supplies and equipment as has been used prior to the giving of such notice of cancellation at the prescribed unit rates stated in the contract, and that the contractor shall agree to accept the return of any and all materials and supplies not used prior to the giving of such notice.