Sts. & Hy. Code, § 100.6

The department may, on behalf of the State of California, enter into agreements with any adjoining state, or any proper agency of such state, for the construction, reconstruction, operation and maintenance, by any party to such agreement, in the manner and by such means as may be provided in the agreement, of bridges over interstate waters and may enter into like agreements with respect to construction, reconstruction, operation and maintenance of highways within this State or such adjoining state, when such highways are at or near the common boundary of the states. Payment for work done pursuant to such agreements may be made from any fund available to the department for highway purposes.