LOCATION ARROWROCK IDEstablished Series
The Arrowrock series consists of shallow, excessively drained soils with rapid permeability that formed in colluvium and residuum from granitic rocks. Slopes range from 35 to 90 percent in foothills and canyons. The average annual precipitation is about 14 inches and the average annual temperature is about 50 degrees F.
TAXONOMIC CLASS: Mixed, mesic, shallow Xeric Torripsamments
TYPICAL PEDON: Arrowrock fine gravelly loamy sand -- on a south-facing slope of 47 percent at 3,400 feet elevation in rangeland. When described on May 13, 1998, the soil was moist to 7 inches and dry below. (Colors are for air-dry soil unless otherwise noted.)
A1--0 to 2 inches; grayish brown (10YR 5/2) fine gravelly loamy sand, dark grayish brown (10YR 4/2) moist; weak fine granular structure; soft, very friable, nonsticky and nonplastic; many very fine roots; many very fine irregular pores; 30 percent fine gravel; neutral (pH 6.8); clear smooth boundary.
A2--2 to 7 inches; brown (10YR 5/3) fine gravelly loamy sand, brown (10YR 4/3) moist; weak fine and medium subangular blocky structure parting to single grain; soft, loose, nonsticky and nonplastic; many very fine roots; many very fine irregular pores; 20 percent fine gravel; neutral (pH 6.8); clear smooth boundary. (combined A horizon - 5 to 12 inches thick)
C--7 to 12 inches; yellowish brown (10YR 5/4) fine gravelly loamy sand, brown (10YR 4/3) moist; single grain; loose, nonsticky and nonplastic; many very fine roots; many very fine irregular pores; 30 percent fine gravel; neutral (pH 6.7); clear wavy boundary. (3 to 8 inches thick)
Cr--12 to 15 inches; weathered granodiorite; gradual wavy boundary. (2 to 6 inches thick)
R--15 inches; unweathered granodiorite.
TYPE LOCATION: Boise County, Idaho; about 2 miles northeast of the U.S.F.S. Lucky Peak Nursery; 250 feet north and 700 feet west of the southeast corner of section 10, T.3 N., R.4 E.; USGS Arrowrock Dam Quadrangle; Latitude - 43 degrees, 36 minutes, 15 seconds N. and Longitude - 115 degrees, 57 minutes, 30 seconds W.; NAD 83.
RANGE IN CHARACTERISTICS:
Ochric epipedon thickness - 5 to 12 inches
Depth to paralithic contact - 10 to 18 inches
Depth to lithic contact - 15 to 20 inches
Particle-size control section - 2 to 8 percent clay; 15 to 35 percent rock fragments
Moisture control section - moist less than 90 consecutive days when the soil temperature is greater than 47 degrees F.
Average annual soil temperature - 50 to 54 degrees F.
A horizon
Value - 3 or 4 moist
Chroma - 2 or 3 dry or moist
Rock fragments - 15 to 35 percent fine gravel
C horizon
Value - 5 through 7 dry, 4 or 5 moist
Chroma - 3 or 4 dry or moist
Texture - LS, LCOS, S or COS
Clay content - 1 to 7 percent
Rock fragments - 15 to 35 percent fine gravel
COMPETING SERIES: These are the Canebrake, Glenbrook, and Solarview series. Canebrake soils are 20 to 40 inches to a lithic contact (hard granite).. Glenbrook soils are greater than 24 inches to a lithic contact and have a base saturation of more than 75 percent throughout. Solarview soils do not have a lithic contact within 60 inches.
GEOGRAPHIC SETTING: Arrowrock soils are on steep and very steep, south-facing canyon walls, hill backslopes and shoulders at elevations of 2,500 to 4,850 feet. These soils formed in colluvium and residuum from granodiorite or related granitic rocks. Slopes range from 35 to 90 percent. The average annual precipitation is 12 to 16 inches. The average annual temperature is 48 to 52 degrees F. The frost-free period is 120 to 155 days.
GEOGRAPHICALLY ASSOCIATED SOILS: These are the Borid and Painter soils. Borid soils are loamy-skeletal and do not have a paralithic contact. Painter soils are moderately deep to a paralithic contact. These soils are on similar geomorphic positions.
DRAINAGE AND PERMEABILITY: Excessively drained; very rapid runoff; rapid permeability.
USE AND VEGETATION: Arrowrock soils are used mainly for rangeland and wildlife habitat. Native vegetation is antelope bitterbrush, basin big sagebrush, needle and thread, and bluebunch wheatgrass.
DISTRIBUTION AND EXTENT: West-central Idaho. MLRA 10. Arrowrock soils are not extensive.
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:
Ochric epipedon - zone from the soil surface to 7 inches (A1 and A2 horizons)
Paralithic contact - at 12 inches (Cr horizon)
Lithic contact - at 15 inches (R)
Particle-size control section - zone from the soil surface to 12 inches
Soil moisture regime - aridic bordering on xeric
These soils are drier than other soils in the region under similar precipitation due to very low water holding capacity, early runoff and extended period of high evapotranspiration.