Protect against water drainage and erosion

Some sections of the city of Manitou Springs have hills of varying degrees of slope. To protect against water drainage and erosion, the city adopted a hillside zoning ordinance that required homes on hillsides to be surrounded by more open land than in the balance of the city. Sellon owned land on a hillside and claimed that the hillside ordinance was unconstitutional because it did not treat all homeowners equally. Was the ordinance valid? [Sefton v. City of Manitou Springs, 745 P.2d 229 (Colo.)]