The grades given and shown in detail upon the plat of the City, as prepared by C.H. Mull, City Engineer, under certificate of said Engineer, dated May 20, 1909, as subsequently amended, and on file in the office of the City Clerk, be and the same are hereby adopted and declared to be the established grades of said City upon the streets and alleys as shown thereon.
The City Engineer shall establish grades for all new streets and alleys taken into the City and for all streets and alleys not now graded and shall file records of the same in the form of profile drawings with the City Clerk. Such grades shall become official upon filing with the City Clerk.
The elevation figures shown upon maps and profile drawings or set forth in ordinances refer to Local Datum which is hereby established by the monument at the corner common to Sections 15, 16, 21 and 22, Township Ten (10) South, Range Seventeen (17) East, B.M., the top of said monument being at elevation 3812.07 feet above sea level. (1958 Code, ch. IV, art. 1)