The Secretary of the Army is authorized to accept from the State of California the use of any dredger, or appliances owned or controlled by said State, conformably to any offer thereof by the said State; and the Secretary of the Army is authorized to use any such dredger or appliances in any river or harbor improvement that may be prosecuted therein by the United States, either on the part of the United States alone or conjointly with said State: Provided, That nothing shall be paid to the State of California for the use of said dredger, and that nothing herein contained shall create any liability against the United States.