LOCATION OBRIEN MTEstablished Series
TAXONOMIC CLASS: Fine-loamy, mixed, superactive, frigid Pachic Haplustolls
TYPICAL PEDON: Obrien clay loam, in rangeland (colors are for dry soil unless otherwise noted).
A1--0 to 5 inches; very dark grayish brown (10YR 3/2) clay loam, very dark brown (10YR 2/2) moist; moderate fine granular structure; slightly hard, firm, moderately sticky and moderately plastic; many very fine roots; many very fine pores; neutral (pH 7.0); clear smooth boundary. (5 to 8 inches thick)
A2--5 to 21 inches; dark grayish brown (10YR 4/2) clay loam, very dark grayish brown (10YR 3/2) moist; moderate medium subangular blocky structure; hard, firm, moderately sticky and moderately plastic; many very fine roots; many very fine pores; neutral (pH 7.0); clear wavy boundary. (11 to 25 inches thick)
Bk1--21 to 37 inches; light brownish gray (2.5Y 6/2) clay loam, grayish brown (2.5Y 5/2) moist; moderate medium subangular blocky structure; hard, firm, moderately sticky and moderately plastic; many very fine roots; common very fine pores; common fine masses and threads of lime; strongly effervescent; moderately alkaline (pH 8.2); clear smooth boundary.
Bk2--37 to 60 inches; light brownish gray (2.5Y 6/2) clay loam, grayish brown (2.5Y 5/2) moist; moderate fine and medium subangular blocky structure; slightly hard, friable, moderately sticky and moderately plastic; common very fine roots; common very fine pores; many fine masses and threads of lime; strongly effervescent; moderately alkaline (pH 8.4).
TYPE LOCATION: Hill County, Montana; 550 feet north and 2,250 feet west of the SE corner of sec. 7, T. 30 N., R. 17 E.
RANGE IN CHARACTERISTICS:
Soil temperature - 43 to 46 degrees F.
Soil moisture control section - between 4 and 12 inches.
Mollic epipedon thickness - 16 to 33 inches.
Depth to Bk horizon - 16 to 33 inches.
A By horizon is allowed.
A horizon - Hue: 10YR or 2.5Y
Value: 3 or 4 dry; 2 or 3 moist
Clay content: 27 to 35 percent
Reaction: pH 6.6 to 7.3
Bk1 horizon - Hue: 10YR or 2.5Y
Value: 5 or 6 dry; 4 or 5 moist
Chroma: 2, 3, or 4
Texture: clay loam, loam
Clay content: 18 to 35 percent
Reaction: pH 7.9 to 8.4
Calcium carbonate equivalent: 1 to 15 percent
EC: less than 4 mmhos/cm
Bk2 horizon - Hue: 10YR or 2.5Y
Value: 5 or 6 dry; 4 or 5 moist
Chroma: 2, 3, or 4
Texture: clay loam, loam
Clay content: 18 to 35 percent
Bulk Density: 1.55 to 1.75
Reaction: pH 7.9 to 9.0
Calcium carbonate equivalent: 1 to 15 percent
EC: less than 4 mmhos/cm
COMPETING SERIES:
Arnegard (ND) - formed in alluvium or colluvium; has a bulk density less then 1.55.
Beman (CO) - formed in alluvium; has a bulk density less then 1.55.
Bowery (MT) - formed in alluvium or colluvium; has a bulk density less then 1.55.
Falkirk (ND) - formed in glaciofluvial sediments 20 to 40 inches thick over till; has two discontinuities.
Garlips (CO) - formed in alluvium or colluvium; has a bulk density less then 1.55.
Garza (WY) - formed in alluvium or colluvium; has a bulk density less then 1.55.
Lonecone (CO) - is 20 to 40 inches deep to a paralithic contact of sandstone.
Molinaro (CO) - formed in alluvium; has a bulk density less then 1.55.
Roseglen (ND) - formed in glaciolacustrine sediments; has a bulk density less then 1.55.
Shawa (CO) - formed in alluvium or colluvium; has a bulk density less then 1.55
Sheckle (UT) - formed in alluvium or colluvium; has a bulk density less then 1.55.
GEOGRAPHIC SETTING:
Landform - back slopes of hills and escarpments.
Elevations - 3,000 to 4,000 feet.
Slope - 15 to 60 percent.
Parent material - till.
Climate - long, cold winters; moist springs; warm summers.
Mean annual precipitation - 13 to 17 inches, most of which falls during spring and early summer.
Mean annual air temperature - 41 to 44 degrees F.
Frost-free period - 90 to 110 days.
DRAINAGE AND PERMEABILITY: Well drained; slow permeability.
USE AND VEGETATION: Obrien soils are used as rangeland. The potential plant community is bearded wheatgrass, rough fescue, slender wheatgrass, tall needle grasses, other perennial grasses, other perennial forbs, quaking aspen, serviceberry, common chokecherry, and other shrubs.
DISTRIBUTION AND EXTENT: Obrien soils are of small extent in north-central Montana.
MLRA SOIL SURVEY REGIONAL OFFICE (MO) RESPONSIBLE: Bozeman, Montana
SERIES ESTABLISHED: Hill County, Montana, 1994; proposed in Hill County, Montana, 1992.
REMARKS: Soil interpretation record: MT1352. Diagnostic horizons and features recognized in this pedon are: a mollic epipedon from the surface to 21 inches (A1, A2 horizons); accumulation of carbonates from 21 to 60 inches (Bk1, Bk2 horizons); and a particle-size control section from 10 to 40 inches (A2, Bk1, part of Bk2 horizon). Obrien soils have a frigid temperature regime and an ustic moisture regime.
ADDITIONAL DATA: Laboratory information--S92MT-041-2.