LOCATION MCDONALD MTEstablished Series
TAXONOMIC CLASS: Fine, illitic, frigid Alfic Argixerolls
TYPICAL PEDON: McDonald cobbly silty clay loam, cultivated (colors are for dry soil unless otherwise noted).
Ap--0 to 7 inches; dark gray (10YR 4/1) cobbly silty clay loam, very dark gray (10YR 3/1) moist; strong fine and medium granular structure, slightly hard, friable, slightly sticky and slightly plastic; many very fine, fine, and medium roots; many very fine tubular pores; 10 percent pebbles, 10 percent cobbles; slightly acid (pH 6.3); clear smooth boundary. (7 to 10 inches thick)
A--7 to 10 inches; dark grayish brown (10YR 4/2) cobbly silty clay loam, very dark grayish brown (10YR 3/2) moist; moderate fine and medium subangular blocky structure; hard, friable, slightly sticky and slightly plastic; many very fine and fine roots; common very fine and fine tubular and interstitial pores; 10 percent pebbles, 10 percent cobbles; slightly acid (pH 6.5); clear wavy boundary. (3 to 6 inches thick)
E--10 to 14 inches; pinkish gray (7.5YR 6/2) cobbly loam, brown (7.5YR 5/2) moist; moderate medium subangular blocky structure parting to strong fine subangular blocky; hard, firm, moderately sticky and moderately plastic; many very fine and fine roots; many very fine and fine tubular pores; 10 percent pebbles, 10 percent cobbles; neutral (pH 6.6); gradual wavy boundary. (4 to 8 inches thick)
Bt1--14 to 27 inches; light brown (7.5YR 6/4) cobbly clay, brown (7.5YR 5/4) moist; moderate coarse prismatic structure parting to strong medium subangular blocky; very hard, firm, moderately sticky and very plastic; many very fine and fine roots; many very fine and fine tubular pores; few thin silt films on ped faces and on pebbles pinkish white (7.5YR 8/2), brown (7.5YR 5/2) moist; common faint continuous clay films on faces of peds; 10 percent pebbles, 10 percent cobbles; neutral (pH 6.8); gradual wavy boundary.
Bt2--27 to 42 inches; pinkish gray (7.5YR 6/2) silty clay, brown (7.5YR 5/4) moist; moderate very coarse prismatic structure; very hard, firm, moderately sticky and moderately plastic; common very fine, few coarse roots; many very fine, few fine tubular pores; common distinct thick continuous clay films on faces of peds and in pores; 5 percent pebbles, 5 percent cobbles; neutral (pH 7.2); clear wavy boundary. (Combined thickness of the Bt horizons is 10 to 35 inches)
Bk1--42 to 53 inches; pinkish gray (7.5YR 7/2) silty clay loam, brown (7.5YR 5/4) moist; moderate medium platy structure; few very fine roots; common very fine tubular pores; very hard, firm, moderately sticky and moderately plastic; 5 percent pebbles, 5 percent cobbles; common seams and masses of lime, strongly effervescent; moderately alkaline (pH 8.1); abrupt boundary. (5 to 15 inches thick)
Bk2--53 to 60 inches; pinkish gray (7.5YR 7/2) silty clay loam, light brown (7.5YR 6/4) moist; weak thick platy structure; very hard, firm, moderately sticky and moderately plastic; few very fine roots; few very fine pores; 5 percent pebbles, 5 percent cobbles; few fine threads of lime, slightly effervescent; moderately alkaline (pH 8.2).
TYPE LOCATION: Lake County, Montana; 1,320 feet south and 150 feet west of the NE corner of sec. 6, T. 19 N., R. 19 W.
RANGE IN CHARACTERISTICS:
Soil temperature - 41 to 46 degrees F.
Moisture control section - between 4 and 12 inches.
Mollic epipedon thickness - 10 to 16 inches.
Depth to Bk horizon - 24 to 45 inches.
Ap and A horizons - Value: 3, 4 or 5 dry; 2 or 3 moist
Chroma: 1 or 2
Texture: silt loam, silty clay loam, or clay loam
Clay content: 18 to 35 percent
Rock fragments: 5 to 35 percent--0 to 15 percent cobbles and stones, 5 to 20 percent pebbles
Reaction: pH 6.1 to 7.3
E horizon - Hue: 7.5YR, 10YR or 2.5Y
Value: 6, 7 or 8 dry; 5 or 6 moist
Chroma: 2 or 3
Texture: loam or silt loam
Clay content: 15 to 27 percent
Rock fragments: 5 to 35 percent--0 to 15 percent cobbles and stones, 5 to 20 percent pebbles
Reaction: pH 6.1 to 7.3
Bt horizons - Hue: 10YR, 7.5YR, or 2.5Y
Value: 6 or 7 dry; 4, 5 or 6 moist
Chroma: 1, 2, 3 or 4
Texture: clay, silty clay or silty clay loam
Clay content: 35 to 60 percent
Rock fragments: 0 to 35 percent--0 to 15 percent cobbles and stones, 0 to 20 percent pebbles
Reaction: pH 6.1 to 7.8
Bk1 horizon - Hue: 7.5YR, 10YR or 2.5Y
Value: 6, 7 or 8 dry; 5, 6 or 7 moist
Chroma: 2, 3 or 4
Texture: silty clay loam or clay loam
Clay content: 27 to 35 percent
Rock fragments: 5 to 35 percent--0 to 15 percent cobbles and stones, 5 to 20 percent pebbles
Calcium Carbonate Equivalent: 5 to 15 percent
Reaction: pH 7.4 to 8.4
Bk2 horizon--Hue: 7.5YR, 10YR or 2.5Y
Value: 5, 6, 7, or 8 dry; 4, 5, 6, or 7 moist
Chroma: 2, 3 or 4
Texture: silty clay loam or clay loam
Clay content: 27 to 35 percent
Rock fragments: 5 to 35 percent--0 to 15 percent cobbles and stones, 5 to 20 percent pebbles
Calcium Carbonate Equivalent: 5 to 15 percent
Reaction: pH 7.4 to 8.4
COMPETING SERIES: There are no competing series.
GEOGRAPHIC SETTING:
Landform - alluvial fans, stream terraces, hills and glacial moraines.
Elevation - 3,000 to 4,800 feet.
Slope - 0 to 30 percent.
Parent material - glacial till, glaciolacustrine deposits and tertiary deposits.
Climate - long, cold winters; moist falls and springs; warm summers.
Mean annual precipitation - 16 to 22 inches.
Mean annual temperature - 39 to 44 degrees F.
Frost-free period - 90 to 125 days.
DRAINAGE AND PERMEABILITY: Well drained; slow permeability.
USE AND VEGETATION: McDonald soils are used for irrigated and nonirrigated crops, pastureland and for timber production. Principal crops are wheat, barley and alfalfa. Native timber species are ponderosa pine and Douglas-fir with an understory of pinegrass, common snowberry, Saskatoon serviceberry, common chokecherry, and Oregon-grape.
DISTRIBUTION AND EXTENT: McDonald soils are of moderate extent in mountain valleys of northwestern Montana.
MLRA SOIL SURVEY REGIONAL OFFICE (MO) RESPONSIBLE: Bozeman, Montana
SERIES ESTABLISHED: Lake County, Montana, 1929 soils report "Soil Survey of the Lower Flathead Valley Area Montana."
REMARKS: Soil Interpretation Records: MT0550, MT0634 and MT1127. Diagnostic horizons and features recognized in this pedon are: a mollic epipedon from the soil surface to 10 inches (Ap, A horizons); an albic horizon from 10 to 14 inches (E horizon); an argillic horizon from 14 to 42 inches (Bt1, Bt2 horizons); a particle-size control section that is the upper 20 inches of the argillic horizon (Bt1, Bt2 horizons). McDonald soils have a frigid temperature regime and a xeric moisture regime bordering on ustic.
ADDITIONAL DATA: S65MT-47-5; S65MT-39-2; S65MT-47-4 clay mineralogy; S65MT47-4, B21t, 23-29 inches, illitic--memo December 6, 1967, Lincoln.