LOCATION CRAGO MT+CO UT WY
Established Series
Rev. DES-KTS-EMM
07/2012
CRAGO SERIES
The Crago series consists of very deep, well drained soils that formed in alluvium or colluvium derived mainly from limestone or basal conglomerate. These soils are on alluvial fans, fan remnants, stream terraces, escarpments, hills and mountain slopes. Slopes range from 0 to 75 percent. Mean annual precipitation is about 12 inches, and mean annual air temperature is about 43 degrees F.
TAXONOMIC CLASS: Loamy-skeletal, carbonatic, frigid Aridic Calciustepts
TYPICAL PEDON: Crago gravelly loam, in grassland (Colors are for dry soil unless otherwise noted.)
A--0 to 4 inches; light brownish gray (10YR 6/2) gravelly loam, grayish brown (10YR 5/2) moist; weak fine granular structure; soft, very friable, slightly sticky, slightly plastic; many very fine and fine roots; 20 percent gravel; slightly effervescent; moderately alkaline (pH 8.0); clear smooth boundary. (2 to 6 inches thick)
Bk1--4 to 10 inches; pale brown (10YR 6/3) gravelly loam, brown (10YR 5/3) moist; weak fine subangular blocky structure; slightly hard, very friable, slightly sticky, slightly plastic; common very fine and fine roots; 35 percent gravel; continuous distinct calcium carbonate casts on undersides of gravel; disseminated calcium carbonate; strongly effervescent; moderately alkaline (pH 8.0); clear smooth boundary. (2 to 8 inches thick)
Bk2--10 to 21 inches; very pale brown (10YR 7/3) very gravelly loam, pale brown (10YR 6/3) moist; weak fine subangular blocky structure; slightly hard, very friable, slightly sticky, slightly plastic; few very fine and fine roots; 60 percent gravel; continuous prominent calcium carbonate casts on surface of gravel; some cementation between individual gravel; disseminated calcium carbonate; strongly effervescent; moderately alkaline (pH 8.2); clear smooth boundary.
Bk3--21 to 37 inches; very pale brown (10YR 7/3) extremely gravelly sandy loam, pale brown (10YR 6/3) moist; weak fine subangular blocky structure; soft, loose, nonsticky, nonplastic; 75 percent gravel; continuous distinct calcium carbonate casts on gravel; some calcium carbonate cementation between individual gravel; disseminated calcium carbonate; violently effervescent; moderately alkaline (pH 8.4); gradual wavy boundary. (Combined thickness of the Bk2 and Bk3 horizons - 10 to 46 inches.)
2C--37 to 60 inches; brownish yellow (10YR 6/6) extremely gravelly loamy sand, yellowish brown (10YR 5/6) moist; massive; loose, nonsticky, nonplastic; 75 percent gravel; disseminated calcium carbonate; strongly effervescent; moderately alkaline (pH 8.4).
TYPE LOCATION: Musselshell County, Montana; 500 feet south and 500 feet west of the northeast corner of sec. 25, T. 11 N., R. 23 E.
RANGE IN CHARACTERISTICS:
Mean annual soil temperature: 40 to 47 degrees F
Depth to the 2C horizon: 34 to 60 inches
Calcium-carbonate equivalent in the 10 to 40 inch zone: 15 to 60 percent of the fine-earth fraction; 40 to 70 percent of the whole soil, including rock fragments less than 3/4-inch
Soil phases: stony, very stony, and alkali
Note: The surface horizon when mixed to 7 inches does not meet the requirements for a mollic epipedon.
A horizon
Hue: 7.5YR, 10YR or 2.5Y; dry or moist
Value: 4 to 6 dry; 3 to 5 moist
Chroma: 2 or 3; dry or moist
Texture: sandy loam, loam or clay loam
Clay content: 15 to 35 percent
Content of rock fragments: 0 to 75 percent--0 to 45 percent gravel, 0 to 30 percent cobbles and stones
Calcium-carbonate equivalent: 0 to 15 percent
Reaction: pH 7.4 to 9.0; Alkali phase: pH 7.9 to 9.0
Bk1 horizon
Hue: 7.5YR, 10YR or 2.5Y; dry or moist
Value: 5 to 8 dry; 4 to 6 moist
Chroma: 2 to 4; dry or moist
Texture: loam, clay loam, sandy clay loam or sandy loam
Clay content: 15 to 35 percent
Content of rock fragments: 15 to 75 percent--15 to 60 percent gravel, 0 to 30 percent cobbles and stones
Calcium-carbonate equivalent: 5 to 15 percent of the fine-earth fraction; 40 to 55 percent of the whole soil, including rock fragments less than 3/4-inch
Reaction: pH 7.4 to 9.0; alkali phase: pH 7.9 to 9.0
Bk2 horizon
Hue: 2.5Y or 10YR; dry or moist
Value: 6 to 8 dry; 4 to 7 moist
Chroma: 2 to 4; dry or moist
Texture: loam, sandy loam, sandy clay loam or clay loam
Clay content: 15 to 35 percent
Content of rock fragments: 35 to 75 percent--35 to 60 percent gravel, 0 to 30 percent cobbles and stones
Calcium-carbonate equivalent: 15 to 30 percent of the fine-earth fraction; 40 to 70 percent of the whole soil, including rock fragments less than 3/4-inch
Reaction: pH 7.4 to 9.0; alkali phase: pH 7.9 to 9.0
Bk3 horizon
Hue: 2.5Y or 10YR; dry or moist
Value: 6 to 8 dry; 4 to 6 moist
Chroma: 2 to 4; dry or moist
Texture: sandy loam, loam, clay loam or sandy clay loam
Clay content: 15 to 30 percent
Content of rock fragments: 40 to 80 percent--40 to 80 percent gravel, 0 to 40 percent cobbles and stones
Calcium-carbonate equivalent: 15 to 30 percent of the fine-earth fraction; 40 to 70 percent of the whole soil, including rock fragments less than 3/4-inch
Reaction: pH 7.4 to 9.4; alkali phase: pH 8.5 to 9.4
2C horizon
Hue: 2.5Y or 10YR; dry or moist
Value: 6 to 8 dry; 4 to 6 moist
Chroma: 2 to 6; dry or moist
Texture: loamy sand, coarse sandy loam, sandy loam or loam
Clay content: 0 to 20 percent
Content of rock fragments: 40 to 80 percent--40 to 80 percent gravel, 0 to 40 percent cobbles and stones; stony phase: 50 to 80 percent--35 to 40 percent gravel, 3 to 40 percent cobbles and stones
Calcium-carbonate equivalent: 10 to 25 percent of the fine-earth fraction; 20 to 50 percent of the whole soil, including rock fragments less than 3/4-inch
Reaction: pH 7.4 to 9.4; alkali phase: pH 8.5 to 9.4
COMPETING SERIES:
Cragnot (CO) - does not have a 2C horizon
Roto (MT) - have a lithic contact at depths of 20 to 40 inches
GEOGRAPHIC SETTING:
Landform: alluvial fans, fan remnants, stream terraces, escarpments, hills and mountain slopes
Elevation: 2,400 to 7,000. (In Colorado, elevations are 6,500 to 8,500 feet.)
Slope: 0 to 75 percent
Parent material: alluvium or colluvium derived mainly from limestone or basal conglomerate
Climate: Long, cold winters; moist springs; warm summers
Mean annual precipitation: 10 to 15 inches
Mean annual temperature: 38 to 45 degrees F
Frost-free period: 70 to 135 days
GEOGRAPHICALLY ASSOCIATED SOILS:
Musselshell (MT) is on similar landforms; is coarse-loamy in the particle-size control section.
DRAINAGE AND PERMEABILITY: Well drained; moderate permeability above the sandy-skeletal material and rapid in the sandy-skeletal material
USE AND VEGETATION: Crago soils are used mainly as rangeland. The potential native vegetation is mainly bluebunch wheatgrass, western wheatgrass, and needle and thread.
DISTRIBUTION AND EXTENT: Crago soils are extensive in Montana; they also occur in Utah, Wyoming, and Colorado. MLRAs - 34A, 35, 43B, 44B, 46, 47, 52, 58A.
MLRA SOIL SURVEY REGIONAL OFFICE (MO) RESPONSIBLE: Bozeman, Montana.
SERIES ESTABLISHED: Upper Musselshell Valley Area, Montana, 1940.
REMARKS: Diagnostic horizons and features recognized in this pedon:
Ochric epipedon - from 0 to 7 inches, mixed (A, part of the Bk1 horizons)
Calcic horizon - from 10 to 37 inches (Bk2, Bk3 horizons)
Particle-size control section - from 10 to 40 inches (Bk2, Bk3, part of 2C horizons)
Carbonatic mineralogy - from 10 to 40 inches -- 40 to 70 percent calcium carbonate equivalent by weight, that includes all soil material including gravel up to 3/4-inch (Bk2, Bk3, part of 2C horizons)
Crago soils have a frigid temperature regime and an ustic moisture regime that borders on aridic.
ADDITIONAL DATA: Soil interpretation records - MT0088, MT0464, MT1004, MT7014, MT1040, MT0886, MT0658, MT0903, MT9044.
11/2006: This description reflects a change in the type location to better illustrate the central concept of Crago.
National Cooperative Soil Survey
U.S.A.