ABSTRACT
In practice, the concept of a geomorphic surface has been used in two ways: a first portion of the land surface, which is specifically defined in space and time, is composed of an erosion surface and the contemporaneous, adjacent and depositional surface. A second portion of a land surface, which is underlain by laterally continuous, well-expressed soil, is dependent upon the continuous nature of the soil to provide the general unifying character for its recognition and mapping, such as the Yarmouth-Sangamon surface of Iowa. For the purposes of a soil–geomorphic analysis, geomorphic surfaces can be ranked into two categories. The higher rank is given to the geomorphic surface that is underlain by soil profile. The lower rank is given to a geomorphic surface that is not underlain by a soil profile. The Sangamon is dominated by soils developed in lllinoian till and ice-contact deposits. Only localized erosion and deposition effected the Sangamon surface on the flat upland portions of area.
