LOCATION ARMITAGE MTEstablished Series
TAXONOMIC CLASS: Fine-loamy over sandy or sandy-skeletal, mixed, superactive, frigid Aridic Natrustalfs
TYPICAL PEDON: Armitage cobbly loam, native grassland. (Colors are for dry soil unless otherwise noted.)
A--0 to 4 inches; grayish brown (10YR 5/2) cobbly loam, dark brown (10YR 3/3) moist; moderate very fine granular structure; soft, very friable, slightly sticky and slightly plastic; many very fine roots; common very fine and fine pores; 15 percent cobbles, 5 percent pebbles; slightly alkaline (pH 7.4); abrupt wavy boundary. (2 to 4 inches thick)
E--4 to 5 inches; light gray (10YR 7/2) cobbly loam, grayish brown (10YR 5/2) moist; weak very fine granular structure; soft, very friable, slightly sticky and slightly plastic; many very fine roots; common very fine and fine pores; 15 percent cobbles, 5 percent pebbles; slightly alkaline (pH 7.8); abrupt wavy boundary. (1 inch to 3 inches thick)
Bt1--5 to 7 inches; pale brown (10YR 6/3) clay, dark brown (10YR 4/3) moist; strong medium columnar structure; very hard, very firm, very sticky and very plastic; few very fine roots within peds, few very fine and fine roots on faces of peds; few very fine and fine pores; many distinct dark yellowish brown (10YR 4/4) clay films on faces of peds and lining pores; moderately alkaline (pH 8.2); abrupt smooth boundary. (1 inch to 4 inches thick)
Bt2--7 to 13 inches; brown (10YR 5/3) clay loam, dark brown (10YR 4/3) moist; moderate medium prismatic structure parting to weak fine angular blocky; very hard, firm, very sticky and very plastic; few very fine and fine roots within peds, few very fine roots on faces of peds; few very fine and fine pores; common distinct dark brown (10YR 3/3) clay films on faces of peds and lining pores; moderately alkaline (pH 8.2); abrupt wavy boundary. (6 to 13 inches thick)
Bk1--13 to 18 inches; light gray (2.5Y 7/2) silt loam, light brownish gray (2.5Y 6/2) moist; weak coarse prismatic structure parting to weak medium angular blocky; hard, firm, slightly sticky and slightly plastic; few very fine roots; few very fine and fine pores; common fine distinct soft masses of lime; violently effervescent; moderately alkaline (pH 8.4); clear wavy boundary. (8 to 20 inches thick)
Bk2--18 to 36 inches; light gray (2.5Y 7/2) silt loam, grayish brown (2.5Y 5/2) moist; weak coarse prismatic structure; slightly hard, firm, slightly sticky and slightly plastic; few very fine roots; few very fine and fine pores; common fine distinct soft masses of lime; violently effervescent; moderately alkaline (pH 8.4); clear wavy boundary. (3 to 5 inches thick)
2C--36 to 60 inches; pale brown (10YR 6/3) extremely gravelly sand, brown (10YR 5/3) moist; single grain; loose, nonsticky and nonplastic; 55 percent pebbles, 10 percent cobbles; slightly effervescent; moderately alkaline (pH 8.0).
TYPE LOCATION: Madison County, Montana; approximately 2,000 feet north and 1,600 feet west of the SE corner of sec. 17, T.9S., R.1E.
RANGE IN CHARACTERISTICS:
Soil temperature: 40 to 44 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 Bk horizon: 10 to 20 inches
Depth to 2C horizon: 20 to 40 inches
A horizon:
Hue: 10YR
Value, dry: 3, 4, or 5
Value, moist: 2 or 3
Chroma: 2 or 3
Texture: loam or clay loam
Clay content: 15 to 32 percent
Rock fragments: 15 to 30 percent
Cobbles: 15 to 25 percent
Pebbles: 0 to 5 percent
Reaction: pH 7.4 to 7.8
E horizon:
Hue: 10YR
Value, dry: 6 or 7
Value, moist: 4 or 5
Chroma: 2
Texture: loam or clay loam
Clay content: 15 to 32 percent
Rock fragments: 15 to 30 percent
Cobbles: 15 to 25 percent
Pebbles: 0 to 5 percent
Reaction: pH 7.4 to 7.8
NOTE: Some E material extends down between the peds of the Bt1 horizon.
Bt1 horizon:
Hue: 10YR
Value, dry: 5 or 6
Value, moist: 4 or 5
Chroma: 2 or 3
Texture: clay
Clay content: 40 to 50 percent
Rock fragments: 0 to 5 percent
Pebbles: 0 to 5 percent
SAR: 15 to 25
EC: 4 to 8 mmhos/cm
Reaction: pH 7.9 to 8.4
Bt2 horizon:
Hue: 10YR
Value, dry: 5 or 6
Value, moist: 4 or 5
Chroma: 2 or 3
Texture: clay loam or loam
Clay content: 24 to 32 percent
Rock fragments: 0 to 5 percent
Pebbles: 0 to 5 percent
SAR: 15 to 25
EC: 4 to 8 mmhos/cm
Reaction: pH 7.9 to 8.4
Bk horizon:
Hue: 10YR or 2.5Y
Value, dry: 6 or 7
Value, moist: 5 or 6
Chroma: 2
Texture: silt loam or fine sandy loam
Clay content: 17 to 20 percent
Fine sand or coarser content: 15 to 50 percent
Rock fragments: 0 to 5 percent
Pebbles: 0 to 5 percent
SAR: 15 to 25
EC: 4 to 8 mmhos/cm
Reaction: pH 7.9 to 8.4
2C horizon:
Hue: 10YR
Value, dry: 5 or 6
Value, moist: 4 or 5
Chroma: 2 or 3
Texture: sand
Clay content: 0 to 10 percent
Rock fragments: 50 to 70 percent
Cobbles: 5 to 15 percent
Pebbles: 45 to 55 percent
Reaction: pH 7.9 to 8.4
COMPETING SERIES: There are no competing series.
GEOGRAPHIC SETTING:
Landform - fans and terraces.
Elevation - 4,900 to 6,500 feet.
Slope - 0 to 8 percent.
Parent material - alluvium over sand and gravel.
Climate - cool with moist springs and hot, dry summers.
Mean annual precipitation - 10 to 14 inches.
Mean annual temperature - 38 to 42 degrees F.
Frost-free period - 90 to 105 days.
DRAINAGE AND PERMEABILITY: Well drained; slow permeability in the Bt1 horizon, very rapid permeability in the 2C horizon.
USE AND VEGETATION: These soils are used mainly as rangeland; a few areas are used for irrigated and dryland crops. The potential native plants are bluebunch wheatgrass, western wheatgrass, needleandthread, and green needle grass.
DISTRIBUTION AND EXTENT: The dry intermountain valley areas of southwestern Montana. The series is inextensive.
MLRA SOIL SURVEY REGIONAL OFFICE (MO) RESPONSIBLE: Bozeman, Montana
SERIES ESTABLISHED: Madison County Area, Montana, 1983.