The information in the soils subsection was extracted from Exploratory Soil Survey of Alaska(Rieger, Schoephorster, and Furbush, 1979). In addition, the soil classification in the Northwest NPR-A Planning Area is identical to that in the Northeast NPR-A Planning Area. See the Northeast NPR-A IAP/EIS for additional information.
Exploratory survey and field mapping of the Northwest NPR-A Planning Area was initiated in 1967 and completed in 1973. Field mapping was done at a scale of 1:500,000 (1 inch = 8 mi). All existing soil maps and reports were used, but the exploratory soil map was based largely on observations made from a small helicopter that landed frequently in roadless areas. Distinctive landscape patterns were identified from the air and delineated on the map. Soils within each landscape segment were described and classified; relationships between the soils, the native vegetation, and landforms were noted; and the proportion of the area occupied by each major type of soil was estimated. Each map unit in this survey was an association of soils arranged in a consistent pattern.
Two major land resource areas (MLRA's) have been identified in the Northwest NPR-A Planning Area: the Arctic Foothills and the Arctic Coastal Plain (Sec. III.A.1.b and Map 28 
). Each MLRA has a unique pattern of topography, climate, vegetation, and soils.
The Soil Taxonomy of the National Cooperative Soil Survey, adopted in 1965, defines soils by their properties rather than by external environmental factors such as climate and vegetation. In the Exploratory Soil Survey of Alaska(Rieger, Schoephorster, and Furbush, 1979), the soils of Alaska are classified at the subgroup level and placed in distinct map units. Five map units occur in the Planning Area (Map 32
).
Map Unit IQ2 occupies most of the northern part of the AFP. It is extensive and widespread in all regions of the permafrost zone. Although the dominant soils have similar characteristics, there are some differences in associated soils of relatively minor extent, soil patterns, landforms, and landscape features. This unit occupies broad valleys, basins, foot slopes, and low rolling piedmont hills. Most areas are patterned with polygons, stripes, and some circular frost scars. Elevations range from 300 ft above sea level near the coastal plains to 3,000 ft on foot slopes of the Brooks Range. Most of the soils are silty colluvial and residual material weathered from fine-grained, nonacid sedimentary rocks. The vegetation consists of tundra dominated by sedges, mosses, lichens, and low shrubs.
Map Unit IQ8 occupies most of the southern part of the AFP featuring the hills and ridges of the Planning Area. It also occupies extensive parts of the foothills north of the Brooks Range. Broad sloping valleys, separated by steep ridges, hills, and knolls dominate the landscape. Elevations range from near sea level on a few foot slopes to about 3,000 ft on hills and ridges near the Brooks Range. Permafrost underlies all areas. The dominant soils in valleys and long foot slopes were formed from loamy colluvial sediment. Most of the soils on hills and ridges consist of very gravelly material weathered from sedimentary rock. A few soils near the Brooks Range were formed from very gravelly glacial drift. The vegetation consists of tundra made of mosses, sedges, lichens, grasses, dwarf shrubs, and small forbs. Vegetative patterns commonly stripe the long slopes and many frost-scarred areas mar hills and ridges. A few windswept peaks are nearly bare. Caribou and other wildlife use the vegetation that is also suitable for reindeer grazing.
Map Unit IQ6 occupies most of the eastern part of the ACP occurring in the Planning Area. With few exceptions, the soils of this unit are shallow and constantly wet as they lie over the area's thick permafrost. Elevations range from sea level to about 400 ft. Many small thaw lakes characterize this treeless area. Low terraces, broad shallow depressions, and floodplains are typical. It is common to find frost features, including polygons, hummocks, frost boils, and pingos. The dominant poorly drained soils have developed principally in deep loamy sediment under a thick cover of sedge tussocks, low shrubs, forbs, mosses, and lichens. Very poorly drained fibrous peat soils, commonly under a cover of sedges, occupy broad depressions, shallow drainage ways, and lake borders. These types of soils are cold and wet. Caribou and a few moose, wolves, and small furbearing animals use the area. It is also a major nesting ground for migratory birds.
Map Unit IQ21 occupies most of the western part of the ACP in the Planning Area. The landscape is dominated by nearly level, low tundra, dotted by shallow thaw lakes. There are many undulating and rolling sand dunes, especially in areas bordering the floodplains of major streams and some of the larger lakes. Most of the dunes are stabilized by vegetation, though some dunes adjacent to streams are active. Elevation ranges from a few feet above sea level near the coast to about 150 ft inland. Sedges, mosses, grasses, lichens, and low shrubs and forbs dominate the arctic tundra in the area. Most of the soils consist of sandy aeolian, alluvial, and marine deposits, but a few were formed in loamy material. Poorly drained soils with a shallow permafrost table occupy most of the nearly level areas and the broad swales between dunes. The soils on dunes consist of aeolian sand and, although they are perennially frozen below a depth of 30 to 40 inches, they seldom retain enough moisture to form large ice crystals. Soils of this unit provide wildlife habitat for species frequenting the arctic tundra, including migrating herds of caribou and nesting waterfowl. The area is potentially suitable for reindeer grazing.
Map Unit IQ22 occupies much of the area along the Colville River through the Arctic Foothills and the ACP. It occupies low terraces, braided floodplains, and broad alluvial fans bordering the Colville River. Elevations range from sea level on the plains bordering the coast to about 2,000 ft in the Brooks Range. The dominant soils consist of very gravelly stream deposits underlain by permafrost. Low parts of the unit are commonly flooded by runoff from spring snowmelt and heavy summer rainstorms in the mountainous watershed areas. The vegetation consists of arctic tundra dominated by sedges, mosses, and low shrubs. Soils of the association provide habitat for wildlife on the arctic tundra and they are potentially suitable for reindeer grazing.