A Generalized Investigation of Potentially Poor Soil Support by Regional Geomorphic Units within the Adjacent 48 States : Preprint

This report qualitatively assesses the potential for poor soil support within the adjacent 48 states. For each of 97 physiographic sections, an estimate was made of: (a) the frequency of occurrence of organic deposits, and (b) the combined frequency of occurrence-severity rating of clayey deposits. In order to assess the regional character of the poor support problem, a national soil textural map was developed. Frequency of occurrence ratings for organic deposits were determined directly from this map for each section. For clayey deposits, a severity scale, based upon a relationship between the soil texture and the Unified Soil Classification System, was combined with the frequency of occurrence rating of clayey deposits obtained from the national soils map. The poor support potential was rated at five levels: (VW) very widespread, (M-W) medium to widespread, (L-M) limited to medium, (N-L) non-existent to limited, and (NE) non-existent. The study indicated the limited regional distribution of organic terrain in the Adjacent 48 States. This distribution is concentrated in youthful (geomorphic) glacial and coastal terrain due to the rather poorly integrated drainage system often associated with these regional geomorphic areas. Although clayey deposits occur throughout the Adjacent 48 States, the greater concentration of them is east of the Rocky Mountains. The climatic, topographic and parent material factors are generally more favorable in the latter areas for the development of clay minerals.