Where such authorization is given, the board of supervisors of the county desiring the construction may:
(a)
Expend, through its own officers or agencies, the amounts authorized by section 1624.
(b)
By resolution transfer such amounts to the account of the commission or to the account of the Secretary of Agriculture of the United States, and may by such resolution specify and determine the location and type of construction of such highway. The amount thus transferred shall, if accepted by the Commission or the Secretary of Agriculture, be expended exclusively for the purpose specified and determined in the resolution.