The board of supervisors, in addition to hearing protests against the proposed work and the extent of the district to be assessed therefor, shall hear and pass upon all protests against the formation of the maintenance district and against the extent thereof, and shall hear and pass upon all protests against the annexation of the territory within which the improvements are to be constructed to an existing maintenance district, and its decision shall be final and conclusive.
Ca. Sts. and High. Code § 5825