Cal. Water Code § 12604

As to any matter involving the United States, its departments or agencies, which is within the scope of the powers and duties of the department, the department may represent the interests of the State or any county, city, state agency or public district, and to that end may correspond, confer and cooperate with the United States, its departments or agencies, and where necessary the director, or his authorized representative, may travel either within or without the State.