LOCATION HILLON MTEstablished Series
TAXONOMIC CLASS: Fine-loamy, mixed, superactive, calcareous, frigid Aridic Ustorthents
TYPICAL PEDON: Hillon loam, grassland (colors are for dry soil unless otherwise noted).
Ap--0 to 3 inches; grayish brown (2.5Y 5/2) loam, very dark grayish brown (2.5Y 3/2) moist; moderate very fine granular structure; slightly hard, very friable, slightly sticky and plastic; many very fine and common fine roots; common very fine pores; mildly alkaline; clear smooth boundary. (1 to 7 inches thick)
Bk1--3 to 16 inches; grayish brown (2.5Y 5/2) loam, dark grayish brown (2.5Y 4/2) moist; weak medium prismatic structure parting to moderate fine and medium subangular blocky; slightly hard, friable, sticky and plastic; many very fine and common fine roots; many very fine pores; many fine and medium masses of lime; violently effervescent; strongly alkaline; clear wavy boundary. (5 to 15 inches thick)
Bk2--16 to 29 inches; light olive brown (2.5Y 5/4) clay loam, olive brown (2.5Y 4/4) moist; moderate fine and medium subangular blocky structure; hard, friable, sticky and plastic; common very fine roots; common very fine pores; common fine and medium masses of lime; violently effervescent; strongly alkaline; clear wavy boundary. (5 to 25 inches thick)
By--29 to 60 inches; light olive brown (2.5Y 5/4) clay loam, olive brown (2.5Y 4/4) moist; moderate fine and medium subangular blocky structure; hard, firm, sticky and plastic; few very fine roots in upper part; few very fine pores; 5 percent pebbles; common fine and medium seams and masses of gypsum below 36 inches; strongly effervescent; strongly alkaline.
TYPE LOCATION: Hill County, Montana; 2,200 feet south and 500 feet west of NE corner of sec. 32, T. 32 N., R. 15 E.
RANGE IN CHARACTERISTICS:
Soil temperature - 41 to 47 degrees F.
Moisture control section - between 4 and 12 inches; dry in all parts between four-tenths and five-tenths of the cumulative days per year when the soil temperature at a depth of 20 inches is 41 degrees F or higher.
Depth to accumulated carbonates - 3 to 9 inches.
Bulk density of till - 1.55 to 1.75 g/ccm.
Bky and Cy horizons are allowed.
The surface layer, when mixed to 7 inches, will not meet the color requirements for a mollic epipedon.
Ap, A horizon - Hue: 10YR or 2.5Y
Value: 5 or 6 dry; 3, 4 or 5 moist
Chroma: 2 or 3
Texture: loam or clay loam
Clay content: 18 to 35 percent
Rock fragments: 0 to 25 percent--0 to 10 percent cobbles and stones, 0 to 15 percent pebbles
Calcium carbonate equivalent: 0 to 10 percent
Effervescence: none to violently
Reaction: pH 7.4 to 8.4
Bk horizon - Hue: 10YR, 2.5Y, or 5Y
Value: 5, 6, or 7 dry; 4, 5, or 6 moist
Chroma: 2, 3, or 4
Texture: loam or clay loam
Clay content: 18 to 35 percent with 25 to 35 percent fine and coarser sand
Rock fragments: 0 to 15 percent pebbles
Calcium carbonate equivalent: 5 to 15 percent
Effervescence: strongly or violently
Reaction: pH 7.9 to 9.0
Bulk density: 1.55 to 1.75 g/ccm
By or Bky horizons - Hue: 10YR, 2.5Y, or 5Y
Value: 5, 6, or 7 dry; 4, 5, or 6 moist
Chroma: 2, 3, or 4
Texture: loam or clay loam
Clay content: 18 to 35 percent with 25 to 35 percent fine and coarser sand
Rock fragments: 0 to 15 percent pebbles
Bulk density: 1.55 to 1.75 g/ccm
Calcium carbonate equivalent: 2 to 15 percent
Effervescence: strongly to violently
SAR: 1 to 20
EC: 1 to 8
Reaction: pH 7.9 to 9.0
COMPETING SERIES:
Benz (MT) - has SAR values greater than 13 throughout the profile; did not form in till that has a bulk density of 1.55 or greater; does not have a horizon of secondary carbonates.
Mussel (MT) - did not form in till that has a bulk density of 1.55 g/ccm or greater.
Patent (ND) - does not have a horizon of secondary carbonate accumulation; formed in stratified alluvium.
GEOGRAPHIC SETTING:
Landform - till plains; hills; escarpments.
Elevation - 1,900 to 4,000 feet.
Slope- 0 to 70 percent.
Parent material - calcareous loam till.
Climate - long cold, dry winters; moist springs and summers.
Mean annual precipitation - 10 to 14 inches.
Mean annual temperature - 39 to 45 degrees F.
Frost-free period - 100 to 135 days.
DRAINAGE AND PERMEABILITY: Well drained; slow permeability.
USE AND VEGETATION: Hillon soils are used mainly for rangeland and for cropland. Potential native vegetation is western wheatgrass, bluebunch wheatgrass, needleandthread, prairie junegrass, blue grama, threadleaf sedge, and needleleaf sedge.
DISTRIBUTION AND EXTENT: Hillon soils are extensive in north-central and northeastern Montana.
MLRA SOIL SURVEY REGIONAL OFFICE (MO) RESPONSIBLE: St. Paul, Minnesota
SERIES ESTABLISHED: Hill County (North Montana Agricultural Research Center), Montana, 1972.
REMARKS: Soil interpretations records: MT0103, MT0674, MT0610. Diagnostic horizons and features recognized in this pedon are: an ochric epipedon from the soil surface to 7 inches, mixed (Ap, Bk1 horizons); horizons of secondary lime accumulation (Bk1, Bk2 horizons); a particle-size control section from 10 to 40 inches (Bk1, Bk2, and part of By horizons). Hillon soils have a frigid temperature regime and an ustic moisture regime bordering on aridic.