PERGELIC SOILS OF THE WESTERN CONTIGUOUS UNITED-STATES - DISTRIBUTION AND TAXONOMY

Pergelic soils have a mean annual soil temperature (50-cm depth) lower than 0-degrees-C and may have permafrost. Although the distribution of these soils in the western contiguous United States is poorly understood, pergelic soils are common in alpine areas of the Rocky Mountains. In alpine areas, permafrost may be a poor diagnostic feature of pergelic soils because it commonly exists below 50 cm, is difficult to detect in hand-excavated pits, and may be relict. The use of ground-ice features to identify pergelic soils is problematic because they may reflect seasonal frost effects or be relict. Soil temperature data are needed to definitively classify pergelic soils. In the United States Soil Taxonomy, pergelic soils are identified at the subgroup level within cryic great groups (e.g., Pergelic Cryorthents). To avoid this mixing of soil temperature classes, pergelic soils should be identified at the great group level (e.g., Geliorthents). Soils containing "dry" permafrost and ice-cemented permafrost could be separated as subgroups.