LOCATION ROBBSCREEK IDEstablished Series
TAXONOMIC CLASS: Fine-loamy, mixed, superactive, mesic Ultic Argixerolls
TYPICAL PEDON: Robbscreek fine gravelly coarse sandy loam -- on a 25 percent convex south-facing slope at 4,280 feet elevation in rangeland. When described on July 19, 1994, the soil was dry throughout. (Colors are for air-dry soil unless otherwise noted.)
A1--0 to 2 inches; grayish brown (10YR 5/2) fine gravelly coarse sandy loam, very dark grayish brown (10YR 3/2) moist; weak fine granular structure; soft, very friable, slightly sticky and slightly plastic; many very fine and fine, common medium and coarse roots; many very fine and fine irregular pores; 20 percent gravel; slightly acid (pH 6.2); clear smooth boundary. (2 to 8 inches thick)
A2--2 to 6 inches; grayish brown (10YR 5/2) fine gravelly coarse sandy loam, very dark brown (10YR 2/2) moist; weak medium platy structure parting to moderate fine and medium subangular blocky; slightly hard, very friable, slightly sticky and slightly plastic; many very fine and fine, common medium and coarse roots; many very fine and fine tubular pores; 15 percent gravel; slightly acid (pH 6.3); clear wavy boundary. (3 to 11 inches thick)
BA--6 to 13 inches; brown (10YR 5/3) fine gravelly coarse sandy loam, very dark brown (10YR 2/2) moist; moderate medium subangular blocky structure; hard, very friable, slightly sticky and slightly plastic; common very fine and fine, few medium and coarse roots; common very fine and fine tubular pores; 15 percent gravel; slightly acid (pH 6.3); clear wavy boundary. (0 to 9 inches thick)
Bt1--13 to 19 inches; yellowish brown (10YR 5/4) fine gravelly sandy clay loam, dark brown (10YR 3/3) moist; strong medium subangular blocky structure; very hard, friable, slightly sticky and slightly plastic; common very fine and fine, few medium and coarse roots; common very fine and fine tubular pores; common distinct clay films on faces of peds and in pores; 15 percent gravel; slightly acid (pH 6.5); gradual wavy boundary. (3 to 10 inches thick)
Bt2--19 to 26 inches; brown (7.5YR 5/4) fine gravelly sandy clay loam, brown (10YR 4/3) moist; strong medium and coarse subangular blocky structure; very hard, friable, slightly sticky and slightly plastic; few very fine and fine roots; common very fine and fine tubular pores; common distinct clay films on faces of peds and in pores; 20 percent gravel; neutral (pH 6.6); abrupt wavy boundary. (6 to 13 inches thick)
Bt3--26 to 30 inches; light brown (7.5YR 6/4) fine gravelly sandy clay loam, dark yellowish brown (10YR 4/4) moist; weak medium prismatic structure parting to strong medium and coarse subangular blocky; very hard, friable, slightly sticky and slightly plastic; few very fine and fine roots; common very fine and fine tubular pores; common distinct clay films on faces of peds and in pores; 30 percent gravel; neutral (pH 6.8); abrupt wavy boundary. (0 to 7 inches thick)
R--30 inches; unweathered granodiorite.
TYPE LOCATION: Boise County, Idaho; about 7.5 miles south and 2.5 miles west of Horseshoe Bend; 850 feet west and 1,500 feet north of the southeast corner of section 32, T.6 N., R.2 E.; USGS Cartwright Canyon Quadrangle; Latitude - 43 degrees, 48 minutes, 40 seconds N. and Longitude - 116 degrees, 14 minutes, 16 seconds W.; NAD 83.
RANGE IN CHARACTERISTICS:
Thickness of mollic epipedon - 7 to 14 inches
Depth to bedrock - 20 to 40 inches
Base saturation - 50 to 75 percent in some part of upper 30 inches
Particle-size control section - 18 to 27 percent clay; more than 25 percent medium or coarser sand; 15 to 35 percent rock fragments
Moisture control section - dry 60 to 90 consecutive days following the summer solstice
Average annual soil temperature - 47 to 53 degrees F.
A horizon
Value - 4 or 5 dry, 2 or 3 moist
Chroma - 2 or 3 dry or moist
Clay content - 12 to 18 percent
Rock fragments - 15 to 25 percent fine gravel
Reaction - moderately acid or slightly acid
Bt horizon
Hue - 10YR or 7.5YR
Value - 5 or 6 dry, 3 or 4 moist
Chroma - 2 through 4 dry or moist
Texture - L or SCL
Clay content - 18 to 27 percent
Rock fragments - 15 to 30 percent gravel, 0 to 5 percent cobbles and 15 to 35 percent total
Reaction - slightly acid or neutral
COMPETING SERIES: These are the Alderpoint (T), Annum, Brownlee, Chirpchatter, Dryfalls (T), Ebadlow, Felton, Fisherhill, Goldendale, Hellake , Lompico, Lorena, Meland, Mendian (T), Meystre, Quiden, Rehfield, Schumacher, Stacker, Stardust, Updegraff and Van Horn series. Annum soils have a mantle of loess, buried Bt horizons and are deep to a paralithic contact. Brownlee soils are deep and very deep. Boyleston soils are very deep and have 0 to 5 percent rock fragments in the particle-size control section. Chirpchatter, Quiden and Stardust soils are very deep and have O horizons. Dryfalls soils are deep and have O horizons. Ebadlow soils are very deep and have 50 to 70 percent rock fragments in the lower part of the particle-size control section. Fisherhill and Goldendale soils are very deep and have less than 5 percent rock fragments. Felton soils have more than 50 percent shale fragments and are deep. Lompico soils are moderately deep to a paralithic contact and have an average annual soil temperature of 56 to 58 degrees F. Hellake soils are very deep and average 0 to 10 percent rock fragments and less than 25 percent medium or coarser sand in the particle-size control section. Lorena and Stacker soils contain less than 5 percent rock fragments and have less than 15 percent medium and coarser sand in the particle-size control section. Meland soils have less than 25 percent medium and coarser sand in the particle-size control section, are dry from 45 to 70 consecutive days and have rock fragments of basalt origin. Mendian soils are very deep and have buried Bt horizons. Meystre are very deep, have O horizons and average 0 to 5 percent rock fragments in the particle-size control section. Rehfield soils are very deep and are dry for 90 to 120 consecutive days. Schumacher have less than 25 percent medium and coarser sand in the particle-size control section and are deep. Updegraff soils have O horizons and are deep. Van Horn soils have average annual soil temperatures greater than 52 degrees F., are micaceous throughout and very deep. Alderpoint soils are not in the database and cannot be competed.
GEOGRAPHIC SETTING: Robbscreek soils are on hill backslopes, summits and shoulders, canyon walls and butte escarpments at elevations of 2,500 to 5,800 feet. Slopes range from 8 to 65 percent. These soils formed in colluvium and residuum from granitic rocks. The average annual precipitation is 13 to 22 inches. The average annual temperature is 45 to 51 degrees F. The frost-free period is 90 to 150 days.
GEOGRAPHICALLY ASSOCIATED SOILS: These are the Brownlee, Cartwright, Dobson, Shimo and Whisk soils. Brownlee and Cartwright soils are greater than 40 inches deep and on similar geomorphic positions. Dobson and Whisk soils are shallow and on summits, shoulders and more convex backslopes. Shimo soils are sandy-skeletal and on similar geomorphic positions.
DRAINAGE AND PERMEABILITY: Well drained; medium to very rapid runoff; moderate permeability.
USE AND VEGETATION: Robbscreek soils are used mainly for rangeland. Small areas are used for irrigated hayland/pasture. Native vegetation is xeric big sagebrush, antelope bitterbrush, bluebunch wheatgrass and Idaho fescue.
DISTRIBUTION AND EXTENT: West-central Idaho. MLRA 10. Robbscreek soils are of moderate extent.
MLRA SOIL SURVEY REGIONAL OFFICE (MO) RESPONSIBLE: Portland, Oregon
SERIES ESTABLISHED: Boise County Area, Idaho, Parts of Ada and Boise Counties, 2005.
REMARKS: Diagnostic horizons and features recognized in this pedon:
Mollic epipedon - zone from the surface to 13 inches (A1, A2 and BA horizons)
Argillic horizon - zone from 13 to 30 inches (Bt1, Bt2 and Bt3 horizons)
Particle-size control section - zone from 13 to 30 inches
Lithic contact - at 30 inches (R)
Soil moisture regime - xeric