The map of total alkalinity of surface waters in the western region illustrates the general patterns of the relative potential sensitivity of surface waters to acidic deposition. As with geology and physiography, surface water alkalinity in the West varies widely. Most all low-alkalinity lakes and streams occur in the glaciated, high-elevation alpine and sub-alpine zones of the numerous mountain ranges. These watersheds are small with steep slopes and thin acidic soils. The lowest alkalinity waters are associated most often with granitic and gneissic rock types, but may also be found in volcanic and certain sedimentary areas. Alkalinity concentrations are generally greater in surface waters at lower elevations and often are extremely high in the intermontane valleys, basins, and plateau areas. (Copyright (c) 1986 Soil Conservation Society of America.)