California Code, Streets and Highways Code - SHC § 2106.5

(a) Each county and any of its incorporated cities may enter into an agreement regarding the base sum established by paragraph (1) of subdivision (c) of Section 2106, providing for expenditure of the amounts apportioned to the county and apportioned for expenditure within the cities participating in the agreement upon roads and streets within the county and the cities participating in the agreement.

(b) Any of the incorporated cities within a county may enter into an agreement among themselves regarding the amount apportioned to them pursuant to paragraph (3) of subdivision (c) of Section 2106 for expenditure upon city streets within the cities participating in the agreement.

(c) Any such agreement shall be filed with the State Controller. After verification of the agreement by the State Controller, the State Controller shall make disposition of the apportionments to the parties participating in the agreement in accordance with terms of the agreement.