LOCATION GERDRUM MT+SDEstablished Series
TAXONOMIC CLASS: Fine, smectitic, frigid Torrertic Natrustalfs
TYPICAL PEDON: Gerdrum clay loam, grassland (colors are for dry soil unless otherwise noted.)
A--0 to 2 inches; grayish brown (10YR 5/2) loam, dark brown (10YR 4/3) moist; weak thin platy structure parting to weak very fine granular; slightly hard, very friable, slightly sticky and nonplastic; common fine and very fine roots; many unstained silt and sand grains; soft very thin vesicular crust on surface; neutral (pH 7.3); clear smooth boundary. (0 to 2 inches thick)
E--2 to 4 inches; pale brown (10YR 6/3) silt loam, dark brown (10YR 4/3) moist; moderate thin platy structure; slightly hard, very friable, slightly sticky and nonplastic; common fine roots; many very fine vesicular pores; many unstained sand and silt grains, with light gray coats on plates; neutral (pH 7.3); abrupt wavy boundary. (Combined A and E horizons 2 to 4 inches thick)
Btn1--4 to 7 inches; brown (10YR 5/3) clay, dark brown (10YR 4/3) moist; strong fine and medium columnar structure parting to moderate medium and fine angular and subangular blocky; extremely hard, firm, sticky and plastic; few fine roots compressed along faces of peds and few very fine roots in matrix; few very fine tubular pores; light gray (10YR 7/2) coats of unstained sand and silt grains on tops of columns; dark grayish brown (10YR 4/2) coats on vertical faces of peds; continuous faint clay films of faces of peds; slightly alkaline (pH 7.8); clear wavy boundary.
Btn2--7 to 14 inches; brown (10YR 5/3) clay, dark brown (10YR 4/3) moist; strong fine and medium prismatic structure parting to strong medium and fine angular blocky; extremely hard, firm, sticky and plastic; few fine and very fine roots compressed along faces of peds and few very fine roots in matrix; few very fine tubular pores; dark grayish brown (10YR 4/2) coats on vertical faces of peds; continuous faint clay films on faces of peds; moderately alkaline (pH 7.9); clear wavy boundary. (The combined thickness of the Btn horizons is 8 to 20 inches)
Btkn--14 to 22 inches; grayish brown (2.5Y 5/2) clay, dark grayish brown (2.5Y 4/2) moist; strong fine and medium prismatic structure parting to moderate fine and medium angular and subangular blocky; very hard, friable, sticky and plastic; few very fine roots; few very fine tubular pores; common faint clay films on vertical faces of peds; common fine masses of lime; strongly effervescent; moderately alkaline (pH 8.4); clear wavy boundary. (0 to 13 inches thick)
Bknyz1--22 to 36 inches; light brownish gray (2.5Y 6/2) clay loam, grayish brown (2.5Y 5/2) moist; moderate medium prismatic structure parting to moderate medium subangular blocky; very hard, friable, sticky and plastic; few very fine roots; few very fine pores; common fine masses of lime; common fine masses and seams of gypsum and other salts; strongly effervescent; moderately alkaline (pH 8.4); clear wavy boundary. (8 to 30 inches thick)
Bknyz2--36 to 46 inches; grayish brown (2.5Y 5/2) sandy clay loam, dark grayish brown (2.5Y 4/2) moist; weak medium prismatic structure parting to weak medium subangular blocky; very hard, friable, slightly sticky and slightly plastic; few very fine roots; few very fine pores; few to common fine masses of lime; common fine masses and seams of gypsum and other salts; strongly effervescent; moderately alkaline (pH 8.4); clear irregular boundary. (0 to 15 inches thick)
2Bknyz--46 to 60 inches; brown (10YR 5/3) gravelly sandy loam, dark brown (10YR 4/3) moist; weak coarse prismatic structure; hard, very friable, slightly sticky and nonplastic; 25 percent pebbles; lime disseminated throughout and as crusts on underside of rock fragments and as seams; common fine masses and seams of gypsum and other salts; strongly effervescent; moderately alkaline (pH 8.4).
TYPE LOCATION: Blaine County, Montana; about 1,740 feet north and 50 feet east of SW corner of sec. 8, T. 25 N., R. 18 E.
RANGE IN CHARACTERISTICS:
Soil Temperature - 42 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 20 inches is 41 degrees F or above.
Depth to k horizon - 10 to 24 inches, in some pedons it is as deep as 40 inches.
Depth to gypsum - 10 to 28 inches.
Soil phases - shaly substratum; gullied.
Some pedons have a BC or Bz horizon below 40 inches and do not have a lithologic discontinuity.
A horizon - Hue: 10YR or 2.5Y
Value: 5, 6, or 7 dry; 4 or 5 moist
Chroma: 2 or 3
Texture: loam, clay loam, silty clay loam, silt loam, clay, silty clay
Clay content: 10 to 50 percent
Rock fragments: 0 to 15 percent pebbles
Reaction: pH 6.6 to 7.8
E horizon - Hue: 10YR or 2.5Y
Value: 6 or 7 dry; 4, 5, or 6 moist
Chroma: 2 or 3
Textures: loam, silt loam, silty clay loam, clay loam, silty clay, or clay
Clay content: 10 to 50 percent
Rock fragments: 0 to 15 percent pebbles
Reaction: pH 6.6 to 7.8
Btn1 horizon - Hue: 10YR or 2.5Y
Value: 5, 6, or 7 dry; 4 or 5 moist
Chroma: 2, 3, or 4
Textures: clay, silty clay, silty clay loam
Clay content: 35 to 55 percent
Rock fragments: 0 to 10 percent pebbles
Structure: fine to coarse columnar or medium or coarse blocky
Hardness: extremely or very hard when dry
EC: 1 to 8 mmhos/cm
SAR: 10 to 20; pedons with sodium adsorption ratio of less than 13 have more exchangeable magnesium plus sodium than calcium plus exchange acidity at pH 8.2.
Reaction: pH 7.4 to 9.0
Btn2 horizon - Hue: 10YR or 2.5Y
Value: 5, 6, or 7 dry; 4 or 5 moist
Chroma: 2, 3, or 4
Textures: clay, silty clay, or silty clay loam
Clay content: 35 to 55 percent
Rock fragments: 0 to 10 percent pebbles
Structure: fine to coarse prismatic or medium or coarse blocky
Hardness: extremely or very hard when dry
EC: 1 to 8 mmhos/cm
SAR: 10 to 20; pedons with sodium adsorption ratio of less than 13 have more exchangeable magnesium plus sodium than calcium plus exchange acidity at pH 8.2.
Reaction: pH 7.4 to 9.0
Btkn horizon - Hue: 10YR, 2.5Y, or 5Y
Value: 5, 6, or 7 dry; 4, 5, or 6 moist
Chroma: 2 or 3
Texture: clay, silty clay, or silty clay loam, clay loam
Clay content: 35 to 55 percent
Rock fragments: 0 to 10 percent pebbles
Calcium carbonate equivalent: 5 to 15 percent
EC: 2 to 8 mmhos/cm
SAR: 13 to 20
Reaction: pH 7.4 to 9.0
Bknyz & Bkyz horizons - Hue: 10YR, 2.5Y, or 5Y
Value: 4, 5, 6, or 7 dry; 4, 5, or 6 moist
Chroma: 2, 3, or 4
Textures: clay loam, sandy clay loam, clay, or silty clay
Clay content: 30 to 50 percent
Rock fragments: 0 to 10 percent pebbles
Calcium carbonate equivalent: 5 to 15 percent
EC: 8 to 16 mmhos/cm
SAR: 13 to 30
Gypsum: 1 to 5 percent
Reaction: pH 7.9 to 9.0
2Bknyz horizon - Hue: 10YR, 2.5Y, or 5Y
Value: 5, 6, or 7 dry; 4, 5, or 6 moist
Chroma: 1, 2, 3, or 4 (1 chroma is lithochromatic)
Textures: sandy loam, loam, sandy clay loam, or silty clay loam
Clay content: 10 to 35 percent
Rock fragments: 15 to 25 percent pebbles
Calcium carbonate equivalent: 5 to 15 percent
EC: 8 to 16 mmhos/cm
SAR: 13 to 30
Gypsum: 1 to 5 percent
Reaction: pH 7.9 to 9.0
COMPETING SERIES:
Creed (MT) - has A and E horizons that have a combined thickness of 4 to 10 inches; very slowly permeable in the Bt horizons.
Elloam (MT) - formed in till that has a bulk density of 1.55 or greater above a depth of 40 inches.
Loburn (SD) - has a combined A and E horizon thickness of more than 4 inches.
Oburn (MT) - is skeletal above a depth of 40 inches.
Thoeny (MT) - formed in till that has a bulk density of 1.55 or greater above a depth of 40 inches.
Waltham (MT) - does not have Btn horizons; formed in till.
Weingart (MT) - has a paralithic contact of semiconsolidated shale at depths of 20 to 40 inches.
GEOGRAPHIC SETTING:
Landform - alluvial fans; stream terraces; sedimentary plains; drainageways; till plains.
Elevation - 1,900 to 5,200 feet. (In Wyoming the elevation is to 7,800 feet)
Slope- 0 to 25 percent.
Parent material - alluvium or glacialfluvial deposits derived mainly from till and sedimentary rock.
Climate - long, cold winters; moist springs; hot, dry summers.
Mean annual precipitation - 10 to 14 inches, most of which falls in the spring and early summer.
Mean annual air temperature - 39 to 45 degrees F.
Frost-free period - 95 to 135 days. (In Wyoming the range is 85 to 135 days)
DRAINAGE AND PERMEABILITY: Well drained; very slow permeability.
USE AND VEGETATION: Gerdrum soils are used mainly for range. A few small areas are used for dryland and irrigated crops. The potential native plant community is mainly western wheatgrass, bluebunch wheatgrass, green needlegrass, needleandthread, forbs, and shrubs.
DISTRIBUTION AND EXTENT: Central and eastern Montana and possibly in adjacent states. Gerdrum soils are extensive.
MLRA SOIL SURVEY REGIONAL OFFICE (MO) RESPONSIBLE: Denver, Colorado
SERIES ESTABLISHED: Blaine County, Montana, 1976.
REMARKS: Soil interpretation records: MT0286, MT0766.
Diagnostic horizons and features recognized in this pedon are: ochric epipedon - from the soil surface to 4 inches (A, E horizons); natric horizon - from 10 to 22 inches (Btn1, Btn2, Btkn horizons); horizons of accumulations of lime and/or gypsum and other salts (Btkn, Bknyz1, Bknyz2, 2Bknyz horizons); particle-size control section - from the top of the argillic horizon to 22 inches (Btn1, Btn2, Btkn horizons). Gerdrum soils have a frigid temperature regime and an ustic moisture regime bordering on aridic.
LABORATORY DATA: S71MT-69-1, S69MT-5-2, S80MT-11-1