LOCATION RIGGINS IDEstablished Series
TAXONOMIC CLASS: Loamy-skeletal, mixed, superactive, mesic Lithic Ultic Argixerolls
TYPICAL PEDON: Riggins very gravelly silt loam, rangeland. (Colors are for dry soil unless otherwise noted.)
A--0 to 8 inches; dark grayish brown (10YR 4/2) very gravelly silt loam, very dark grayish brown (10YR 3/2) moist; moderate fine granular structure; slightly hard, friable, slightly sticky and slightly plastic; many very fine and fine roots; many fine irregular pores; 30 percent gravel and 10 percent cobblestones; neutral (pH 6.8); gradual wavy boundary. (4 to 10 inches thick)
Bt--8 to 13 inches; brown (10YR 4/3) very gravelly clay loam, very dark grayish brown (10YR 3/2) moist; weak subangular blocky structure; hard, firm, sticky and plastic; common very fine and fine roots; many very fine and fine tubular pores; 35 percent gravel and 10 percent cobblestones; distinct nearly continuous clay films on faces of peds and in pores; neutral (pH 6.8); clear wavy boundary. (4 to 12 inches thick)
R--13 inches; basalt.
TYPE LOCATION: Idaho County, Idaho; about 7 1/2 miles southwest of Boles; about 2,000 feet east and 750 north of the southwest corner of sec. 17, T.29N., R.2W.
RANGE IN CHARACTERISTICS:
Thickness of the solum and depth to bedrock - 10 to 20 inches
Rock fragments in the particle-size control section - average 35 to 75 percent
Average annual soil temperature - 47 to 51 degrees F.
Average summer soil temperature - 61 to 66 degrees F.
Soil moisture control section - dry 45 to 75 days in late summer and fall
Base saturation - 60 to 75 percent
A horizon
Value - 4 or 5 dry, 2 or 3 moist
Chroma - 1 to 3 dry or moist
Bt horizon
Hue - 7.5YR or 10YR
Value - 3 or 4 dry, 2 or 3 moist
Chroma - 2 or 3 dry or moist
Texture - GRV-L, GRV-CL
Rock fragments - dominantly gravel but may contain up to 15 percent cobblestones
Reaction - neutral or slightly acid
COMPETING SERIES: These are the Lacy and Ragpie series. Lacy soils are slightly acid to strongly acid in the Bt horizon and the rock fragments in the particle-size control section are dominantly cobbles and stones. Ragpie soils have lime accumulations at the contact between the argillic horizon and the bedrock and have average annual precipitation of 14 to 16 inches.
GEOGRAPHIC SETTING: Riggins soils are on south-facing slopes and have gradients of 4 to 75 percent. They formed in loess mixed with residuum and colluvium from Columbia River basalt or Seven Devils volcanics. Elevation is 2,000 to 5,000 feet. The subhumid climate has moderately dry summers. Average annual precipitation is 16 to 22 inches. Average annual temperature is 45 degrees to 50 degrees F. Frost-free season is about 110 to 140 days.
GEOGRAPHICALLY ASSOCIATED SOILS: These are the Bluesprin, Meland, Lithic Xerorthents and Ferdinand soils. Bluesprin, Ferdinand and Meland soils are deeper than 20 inches to bedrock. Lithic Xerorthents are less than 10 inches deep to bedrock.
DRAINAGE AND PERMEABILITY: Well drained; medium to very rapid runoff; moderately slow permeability.
USE AND VEGETATION: Used mainly for rangeland. Vegetation is mainly Idaho fescue, bluebunch wheatgrass and Sandberg bluegrass.
DISTRIBUTION AND EXTENT: Northern Idaho. The series is moderately extensive.
MLRA SOIL SURVEY REGIONAL OFFICE (MO) RESPONSIBLE: Portland, Oregon
SERIES ESTABLISHED: Idaho County, Idaho, 1976.
REMARKS: Diagnostic horizons and features recognized in this pedon are:
Mollic epipedon - the zone from 0 to 13 inches (A and Bt horizons)
Argillic horizon - the zone from 8 to 13 inches (Bt horizon)
Particle-size control section - the zone from 0 to 13 inches (A and Bt horizon). In soils that are 14 to 20 inches to bedrock the particle-size control section is the argillic horizon.