LOCATION MOUNTAINBOY IDEstablished Series
TAXONOMIC CLASS: Loamy-skeletal, carbonatic, shallow Calcic Duricryolls
TYPICAL PEDON: Mountainboy gravelly silt loam - on an east-facing slope of 2 percent, rangeland, at 7,150 feet elevation. (Colors are for dry soil unless otherwise stated. When described on May 13, 1981, the soil was moist throughout.)
A--0 to 6 inches; brown (10YR 5/3) gravelly silt loam, dark brown (10YR 3/3) moist; weak fine subangular blocky structure parting to weak fine granular; soft, friable, slightly sticky and slightly plastic; many very fine and fine, and common medium and coarse roots; many very fine and fine irregular pores; 20 percent gravel; calcium carbonate coatings less than 1 mm thick on undersides of rock fragments; strongly effervescent; slightly alkaline (pH 7.8); clear smooth boundary. (3 to 6 inches thick)
AB--6 to 11 inches; brown (10YR 5/3) gravelly loam, dark brown (10YR 3/3) moist; weak medium subangular blocky structure; slightly hard, friable, slightly sticky and slightly plastic; common very fine, fine, and coarse and few medium roots; many very fine and fine irregular pores; 25 percent gravel; calcium carbonate coatings, less than 1 mm thick, on the underside of rock fragments; strongly effervescent (55 percent calcium carbonate equivalent); moderately alkaline (pH 8.1); clear wavy boundary. (3 to 6 inches thick)
Bk--11 to 16 inches; light gray (10YR 7/2) very gravelly loam, pale brown (10YR 6/3) moist; weak fine subangular blocky structure; slightly hard, friable, slightly sticky and slightly plastic; few very fine, fine and coarse roots; common very fine and fine irregular pores; 40 percent gravel; calcium carbonate coatings, about 1 mm thick, on rock fragments; violently effervescent (65 percent calcium carbonate equivalent); moderately alkaline (pH 8.4); abrupt wavy boundary. (4 to 8 inches thick)
2Bkq--16 to 19 inches; light gray (10YR 7/2) discontinuous weakly cemented extremely gravelly coarse sand, light yellowish brown (10YR 6/4) moist; massive; hard, firm, nonsticky and nonplastic; common fine and medium irregular pores; 60 percent of horizon is weakly cemented with calcium carbonate and silica, 40 percent is not cemented; 60 percent gravel; violently effervescent (70 percent calcium carbonate equivalent); very strongly alkaline (pH 9.1); abrupt wavy boundary. (3 to 12 inches thick)
2Bkqm--19 to 20 inches; light gray (10YR 7/2) strongly cemented duripan, light yellowish brown (10YR 6/4) moist; root mat on top of pan; abrupt wavy boundary. (0.5 to 1 inch thick)
2B'kq--20 to 60 inches; multicolored extremely gravelly loamy coarse sand; single grain; loose; many fine and medium irregular pores; calcium carbonate and silica pendants, 1 to 2 mm thick, on undersides of rock fragments; 80 percent gravel, 5 percent cobbles; violently effervescent (75 percent calcium carbonate equivalent); very strongly alkaline (pH 9.1).
TYPE LOCATION: Lemhi County, Idaho; 1 mile east of Charcoal Kilns; about 1,900 feet east and 500 feet south of the northwest corner sec. 5, T. 11 N., R. 28 E. Latitude - 44 degrees, 19 minutes, 13 seconds North; Longitude - 113 degrees, 09 minutes, 06 seconds West.
RANGE IN CHARACTERISTICS:
Average annual soil temperature - 39 to 41 degrees F.
Average summer soil temperature - 55 to 58 degrees F.
The soil is dry throughout the moisture control section for 90 to 120 consecutive days following the four months following the summer solstice (Xeric).
Mollic thickness - 8 to 13 inches
Depth to duripan - 15 to 20 inches
Depth to calcic horizon - 8 to 13 inches
Particle-size control section:
Percent clay - 10 to 18;
Rock fragments - 35 to 65 percent
Calcium carbonate equivalent - 55 to 65 percent
A horizon
Value - 4 or 5 dry, 2 or 3 moist
Chroma - 2 or 3 dry or moist
AB and Bk horizons
Value - 5 through 7 dry, 3 through 6 moist
Chroma - 2 or 3 dry or moist
Texture - GR-L, GRV-L, GR-SIL, or GRV-SIL
2Bkq horizon
Value - 6 or 7 dry or moist
Chroma - 2 through 4 dry or moist
2B'kq horizon
Texture - GRX-LCOS, GRX-COSL
Rock fragments - 65 to 85 percent
COMPETING SERIES: There are no other series in this family.
GEOGRAPHIC SETTING: Mountainboy soils are on outwash fans, fan terraces, and fan remnants and have slopes of 2 to 8 percent. Elevations are 6,800 to 8,000 feet. The soils formed in mixed alluvium from sedimentary and metamorphic rock with some loess influence in the surface. The climate is cold and moist in winter and spring and cool and dry in summer. Average annual precipitation ranges from 12 to 16 inches. Average summer temperature is 53 to 55 degrees F and average annual temperature is 37 to 39 degrees F. Frost-free period is 30 to 60 days.
GEOGRAPHICALLY ASSOCIATED SOILS: These are the Arbus, Fandow, and Wiggleton soils. Arbus soils are on fan terraces and lack duripans. Fandow soils are on fan terraces and have ochric epipedons. Wiggleton soils are on fan terraces, are sandy-skeletal and lack duripans.
DRAINAGE AND PERMEABILITY: Well drained; slow runoff; moderate permeability.
USE AND VEGETATION: Rangeland. Vegetation is mainly low sagebrush and bluebunch wheatgrass.
DISTRIBUTION AND EXTENT: East-central Idaho. These soils are not extensive.
MLRA SOIL SURVEY REGIONAL OFFICE (MO) RESPONSIBLE: Portland, Oregon
SERIES ESTABLISHED: Lemhi County, Idaho, 1999.
REMARKS: Diagnostic features recognized in this pedon are:
Mollic epipedon - The zone from 0 to 11 inches (A and AB horizons)
Calcic horizon - The zone from 11 to 19 inches (Bk and 2Bkq horizons)
Duripan - The zone from 19 to 20 inches (2Bkqm horizon)
The particle-size control section is the zone from 10 to 19 inches (part of the AB horizon, and the Bk and 2Bkq horizons)
Soil moisture regime - xeric
This series would be reclassified to a Calcic Duricryolls if and when the subgroup is approved.