The official city base or plane of reference for elevations in the city is hereby fixed at a point at mean low tide referred to as the official bench mark of the United States geological survey, bearing the Red Lodge datum.
The rectangle set out in the stone footing wall of the Pioneer Building, which seat is at a point north 15.8 feet from the southwest corner of block nine and at 1.7 feet above the sidewalk level, is hereby declared to be the primal bench mark of the city, and the elevation thereof is four thousand nine hundred ninety and eighty three one-hundredths feet (4,990.83') above the mean low tide.
All official elevations hereafter established in the city shall be described with reference to their elevation as compared with the official base in feet and decimal parts of a foot. No grade or official elevation shall be established other than by ordinance, and in the manner described in this section. (1960 Compilation § 15-104)