Vehicle Code § 35251

(a) A boom or mast which is designed to be raised and lowered by hydraulic mechanisms and which is a constituent part of or an attachment to a vehicle or machine, shall be securely chained or otherwise restrained to ensure compliance with Section 35250 while the vehicle or machine is being transported as a load or driven upon any highway.

(b) Subdivision (a) does not apply when the configuration and design of the hydraulic boom effectively restrain the movement of the boom during transit.