Gypsum Soil Morphology and Interpretations: An Interim Report from the NCSS Gypsum Soils Task Force

The assessment of gypsum soils has increased in importance with progressive soil mapping in the western United States. Unique challenges associated with high-gypsum soils include soil mapping, description of soil morphology, taxonomic classification, soil interpretations, and laboratory analyses. Equally important is an understanding of soil genesis and soil-landscape processes, particularly in relation to hydrology, surface stability, and landscape evolution. Soil characterization data from the National Soil Survey Laboratory indicates that about 40 percent gypsum content is a valid separation between high-gypsum soils and lower content gypsum soils, based on measured 1500 kPa water content. This critical value was used in proposals to revise mineralogy class, new terms in lieu of texture, and new substitutes for particle-size class for soils that have their physical and chemical properties dominated by the presence of gypsum. Additional proposals include revisions on describing the morphology of gypsum accumulations. The impact of gypsum presence on soil interpretations, specifically gypsum dissolution and removal, has prompted revisions to several soil interpretations related to subsidence.