Soils of the Rocky Mountain and Inland Pacific Northwest Region: LRRs B and E

Abstract

The Rocky Mountain and Inland Pacific Northwest Region is made up of two Land Resource Regions (LRRs)—the Rocky Mountain Range and Forest Region (LRR E) and the Northwestern Wheat and Range Region (LRR B). Soils of these LRRs encompass 694,130 km² in eight western states and have formed in an extremely wide range of parent materials, vegetation, climate, and terrain attributes. As a result, soil properties across the region vary considerably. The climate throughout much of this region is generally dry but can change dramatically with elevation. Overall, precipitation is limited during the growing season and most soils have aridic, xeric , or ustic soil moisture regimes . Temperature regimes are also closely tied to elevation and range from mesic to gelic . Because of the extreme climatic variations, grassland, shrubland, and forest communities may all be found across a relatively small geographic area. This region is home to some of the most dramatic landscapes found in the USA including lava flows, high plateaus, deep canyons, foothills, and rugged mountains. Many of the landscapes were glaciated or affected by periglacial processes and are therefore relatively young. Holocene volcanic eruptions have influenced many soils of the region as well. Mollisols and Aridisols are the dominant soil orders, but Alfisols, Andisols, Entisols, and Inceptisols are also well represented. This chapter describes the general distribution of soils across the Rocky Mountain and Inland Pacific Northwest Region and their characteristics. The role of the soil-forming factors—parent material, climate , organisms, relief, and time —in the development of the region’s soils is emphasized along with the soil and environmental factors influencing land use and management .