The Ida Grove, Iowa, datum plane or permanent bench mark, having an elevation of 1,235.63, is the top of a brass plate in a concrete monument, southeast corner of Lot E, Southeast Quarter (SE 1/4), of the Southeast Quarter (SE 1/4), Section 15, T-87-N, R-40-W, city of Ida Grove, Ida County, Iowa. Said bench mark was established by a U.S.G.S. survey. [Code 1975 § 8-1.0601.]