LOCATION MILLPOCKET MT
Established Series
Rev. MJH-GLS-KLS
05/2023
MILLPOCKET SERIES
The Millpocket series consists of very deep, well drained, sodium affected soils on lake plains and terraces. These soils formed in lacustrine or glaciolacustrine deposits. Slope is 2 to 8 percent. The average annual precipitation is about 460 mm, and the average annual air temperature is about 6 degrees C.
TAXONOMIC CLASS: Fine, mixed, active, frigid Typic Natrixeralfs
TYPICAL PEDON: Millpocket silty clay loam, forested. (Colors are for dry soil unless otherwise noted.)
Oi--0 to 3 cm; undecomposed and partially decomposed forest litter.
E--3 to 21 cm; light gray (10YR 7/2) silty clay loam, grayish brown (10YR 5/2) moist; moderate medium subangular blocky structure; slightly hard, firm, sticky and plastic; many fine and medium and few coarse roots; many fine interstitial pores; neutral (pH 6.8); clear smooth boundary. (13 to 25 cm thick)
E/Bt--21 to 31 cm; E part (60 percent) is light gray (10YR 7/2) silty clay loam, grayish brown (10YR 5/2) moist; Bt part (40 percent) is very pale brown (10YR 7/4) silty clay, yellowish brown (10YR 5/4) moist; strong medium angular blocky structure; hard, firm, sticky and plastic; common fine and few coarse roots; many very fine and fine and common medium tubular pores; common prominent clay films on faces of peds; neutral (pH 7.0); gradual smooth boundary. (0 to 20 cm thick)
Bt--31 to 54 cm; very pale brown (10YR 7/4) silty clay, yellowish brown (10YR 5/4) moist; strong medium angular blocky structure; hard, very firm, sticky and very plastic; common fine and few coarse roots; many very fine and fine tubular pores; many distinct clay films on faces of peds and in pores; neutral (pH 7.2); gradual smooth boundary. (18 to 38 cm thick)
Btnk--54 to 74 cm; very pale brown (10YR 7/4) silty clay, light yellowish brown (10YR 6/4) moist; moderate medium angular and subangular blocky structure; hard, firm, very sticky and plastic; common fine and few coarse roots; common fine interstitial pores; few faint clay films on faces of peds; strongly effervescent, common soft masses of calcium carbonate; moderately alkaline (pH 8.4); gradual smooth boundary. (18 to 38 cm thick)
Bnk--74 to 102 cm; very pale brown (10YR 7/4) silty clay, light yellowish brown (10YR 6/4) moist; weak medium subangular blocky structure; slightly hard, firm, very sticky and plastic; few fine roots; few fine interstitial pores; strongly effervescent, common soft masses of calcium carbonate; moderately alkaline (pH 8.4); gradual smooth boundary. (20 to 38 cm thick)
BC--102 to 155 cm; very pale brown (10YR 8/3) silty clay, light yellowish brown (10YR 6/4) moist; massive; slightly hard, firm, very sticky and plastic; slightly effervescent, disseminated lime; moderately alkaline (pH 8.2).
TYPE LOCATION: Sanders County, Montana; about 915 meters south, 595 meters west of the northeast corner of sec. 17, T. 23 N., R. 24 W.
RANGE IN CHARACTERISTICS:
Soil temperature--6 to 8 degrees C
Soil moisture control section--10 to 30 cm
Soils are moist more than half the time, the soil temperature is greater than 5 degrees C and dry 50 to 100 days following the summer solstice in most years.
Depth to calcium carbonate accumulation--38 to 76 cm
Some profiles contain varved lake sediments.
E horizon
Value--6 or 7 dry; 4, 5, or 6 moist
Clay content--27 to 40 percent
Reaction--pH 6.6 to 7.3
E/Bt horizon
Value--E and Bt: 6 or 7 dry; 5 or 6 moist
Chroma--E part: 2; B part: 3 or 4
Texture--E part: silty clay loam; B part: silty clay or silty clay loam
Clay content--35 to 50 percent
EC--less than 1 mmhos/cm
SAR--less than 13
Reaction--pH 6.6 to 7.8
Bt horizon
Value--6 or 7 dry; 5 or 6 moist
Chroma--3 or 4
Texture--silty clay or silty clay loam
Clay content--35 to 60 percent
EC--less than 1 mmhos/cm
SAR--4 to 13
Reaction--pH 6.6 to 7.8
Btnk and Bnk horizons
Value--6 or 7 dry; 5 or 6 moist
Chroma--3 or 4
Texture--silty clay or silty clay loam
Clay content--35 to 55 percent
Calcium carbonate equivalent--5 to 10 percent
EC--1 to 2 mmhos/cm
SAR--13 to 30
Reaction--pH 7.9 to 9.0
BC horizon
Value--6, 7 or 8 dry; 5 or 6 moist
Chroma--3 or 4
Texture--silty clay or silty clay loam
Clay content--30 to 50 percent
Calcium carbonate equivalent--0 to 5 percent
EC--less than 2 mmhos/cm
SAR--4 to 20
Reaction--pH 7.4 to 9.0
This horizon may have varved lake sediments.
COMPETING SERIES: There are no competing series.
GEOGRAPHIC SETTING:
Landform--lake plains and terraces
Elevation--850 to 980 meters
Slope--2 to 8 percent
Parent material--lacustrine or glaciolacustrine deposits
Climate--long, cold winters; moist springs and falls; dry summers
Mean annual precipitation--430 to 480 mm, much of which falls as snow and spring rains
Mean annual air temperature--5 to 7 degrees C
Frost-free period--90 to 110 days
GEOGRAPHICALLY ASSOCIATED SOILS: None listed.
DRAINAGE AND PERMEABILITY: Well drained; very slow permeability.
USE AND VEGETATION: These soils are used as woodland and pasture. The potential native vegetation is ponderosa pine, common snowberry, pinegrass, white spirea and chokecherry.
DISTRIBUTION AND EXTENT: These soils are of limited extent in the intermountain valleys of northwestern Montana; MLRA 44A.
SOIL SURVEY REGIONAL OFFICE (SSRO) RESPONSIBLE: Bozeman, Montana
SERIES ESTABLISHED: Sanders County, Montana 1997.
REMARKS: Soil interpretation record: MT1223.
Diagnostic horizons and features recognized in this pedon are:
Argillic horizon--31 to 74 cm (Bt and Btnk horizons)
Horizons of calcium carbonate accumulation--54 to 102 cm (Btnk and Bnk horizons)
Horizons of sodium accumulation--54 to 102 cm (Btnk and Bnk horizons)
Particle-size control section--31 to 74 cm (Bt and Btnk horizons)
ADDITIONAL DATA: Lab Sample--S88MT-089-006
Millpocket soils have a frigid temperature regime and a xeric soil moisture regime.
Converted to metric and O horizons were updated to start at zero. Competing series section was not updated. 05/2023
National Cooperative Soil Survey
U.S.A.