Upon the presentation of a petition requesting that the District Investigation Law of 1933 be declared inapplicable to the proceedings, the clerk of the board of supervisors shall immediately refer the same to an appropriate county officer, who shall certify to the board the number of owners of taxable property within the boundaries of the proposed district whose names appear on said petition, together with the percentage of the total assessed valuation of all taxable property within the boundaries of the proposed district, which said signatures represent.