Cal. Sts. & Hy. Code § 2009
The board of supervisors shall act as the policymaking body with respect to county highway matters and shall by appropriate action establish the general policies to be followed by the road commissioner in the administration of his department. The road commissioner shall administer his department and carry out the general policies of the board in conformity with the estimates of expenditures fixed in the budget as finally adopted by the board or as thereafter revised by appropriate action of the board. The commissioner shall employ such assistants and employees as may be necessary, in conformity with the budget and county policies and procedure with respect to personnel and subject to the approval of the board of the salary or other compensation to be paid. The commissioner shall have sole supervision and jurisdiction over personnel and over the assignments of personnel engaged in work on county roads. The commissioner may purchase, lease, or hire such equipment as may be necessary for county road purposes, in conformity with the budget and policies of the county with respect to purchases and rentals and subject to approval of the board as to the price or rental. The commissioner shall have sole jurisdiction over the assignment of equipment used for county road work.
Ca. Sts. and High. Code § 2009