LOCATION ROTO MT+CO UT WYEstablished Series
TAXONOMIC CLASS: Loamy-skeletal, carbonatic, frigid Aridic Calciustepts
TYPICAL PEDON: Roto channery loam, grassland (colors are for dry soil unless otherwise noted).
A--0 to 3 inches; dark grayish brown (10YR 4/2) channery loam, very dark grayish brown (10YR 3/2) moist; weak very fine granular structure; slightly hard, very friable, slightly sticky and slightly plastic; many very fine roots; 25 percent angular pebbles, 5 percent angular cobbles; disseminated lime; faint lime coatings on undersides of fragments; strongly effervescent; moderately alkaline (pH 8.0); clear smooth boundary. (2 to 5 inches thick)
Bk1--3 to 8 inches; pale brown (10YR 6/3) very channery loam, brown (10YR 4/3) moist; moderate fine and medium subangular blocky structure; slightly hard, very friable, slightly sticky and slightly plastic; many very fine roots; many very fine tubular and interstitial pores; 45 percent angular pebbles, 5 percent angular cobbles; many distinct white lime casts on undersides of fragments; common fine seams and masses of segregated white lime; violently effervescent; moderately alkaline (pH 8.2); gradual smooth boundary.
Bk2--8 to 18 inches; very pale brown (10YR 8/2) very channery loam, light gray (10YR 7/2) moist; weak fine and medium subangular blocky structure; slightly hard, friable, slightly sticky and slightly plastic; common very fine roots; many very fine tubular and interstitial pores; 45 percent angular pebbles, 10 percent angular cobbles; continuous distinct white lime casts on undersides of fragments; common fine seams and masses of segregated white lime; violently effervescent; moderately alkaline (pH 8.4); gradual smooth boundary.
Bk3--18 to 32 inches; light gray (10YR 7/2) very channery loam, brown (10YR 5/3) moist; weak fine subangular blocky structure; slightly hard, friable, slightly sticky and slightly plastic; common very fine roots; many very fine tubular and interstitial pores; 50 percent angular pebbles, 10 percent angular cobbles; continuous distinct white lime casts on undersides of fragments; common fine seams and masses of segregated white lime; violently effervescent; moderately alkaline (pH 8.4); abrupt wavy boundary. (Combined thickness of Bk horizons is 15 to 35 inches)
R--32 inches; light gray (10YR 7/1) hard limestone.
TYPE LOCATION: Jefferson County, Montana; 900 feet south and 1,750 feet east of the NW corner of sec. 36, T. 2 N., R. 1 W.
RANGE IN CHARACTERISTICS:
Soil moisture: The soil moisture control section is between 4 and 12 inches and is affected by moist springs and dry summers. Ustic soil moisture regime bordering on aridic.
Soil temperature: 40 to 46 degrees F.
Depth to calcic horizon: 2 to 5 inches.
Depth to lithic contact: 20 to 40 inches to limestone bedrock
Surface rockiness: 0 to 0.1 percent stones and boulders
The surface layer, when mixed to a depth of 7 inches, does not meet the color requirements of a mollic epipedon.
A horizon:
Hue: 10YR to 2.5Y
Value: 4, 5, or 6 dry; 3 or 4 moist
Chroma: 1, 2, or 3
Clay content: 10 to 25 percent
Rock fragments: 10 to 35 percent--0 to 10 percent cobbles and stones; 10 to 25 percent pebbles
Calcium carbonate equivalent: 10 to 25 percent
Reaction: pH 7.9 to 8.4
Bk horizons:
Hue: 10YR or 2.5Y
Value: 5, 6, 7, or 8 dry; 4, 5, 6, or 7 moist
Chroma: 2, 3, 4,
Clay content: 10 to 27 percent
Rock fragments: 35 to 65 percent--5 to 10 percent cobbles; 30 to 55 percent pebbles
Calcium carbonate equivalent: 40 to 60 percent including rock fragments less than 20 mm
Reaction: pH 7.9 to 9.0
COMPETING SERIES: There are the Crago and Cragnot series.
Crago and Cragnot do not have a lithic contact within 60 inches of the mineral soil surface.
GEOGRAPHIC SETTING:
Landform: sedimentary uplands, mountains, strath terraces and structural benches
Elevations: 3,800 to 6,500 feet.
Slopes: 2 to 60 percent.
Parent material: slope alluvium and colluvium over residuum derived from limestone
Climate: long, cold winter; moist springs; hot, dry summers.
Mean annual precipitation: 10 to 14 inches.
Mean annual air temperature: 38 to 44 degrees F.
Frost-free period: 70 to 120 days.
GEOGRAPHICALLY ASSOCIATED SOILS:
DRAINAGE AND PERMEABILITY: Well drained; very low to high runoff; moderate permeability.
USE AND VEGETATION: Roto soils are used mainly for rangeland. Potential native vegetation is mainly bluebunch wheatgrass, blue grama, needleandthread, western wheatgrass, plains reedgrass, prairie junegrass, Sandberg bluegrass, broom snakeweed, fringed sagewort, and juniper. Some areas have widely scattered ponderosa pine, limber pine, and common juniper.
DISTRIBUTION AND EXTENT: Roto soils are of moderate extent in southwestern Montana, northwestern Colorado, and northeastern Utah.
MLRA SOIL SURVEY REGIONAL OFFICE (MO) RESPONSIBLE: Bozeman, Montana
SERIES ESTABLISHED: Utah soil survey, 1990. Lewis and Clark County, Montana, 1979. Series moved to Jefferson County, Montana, 1993.
REMARKS: Soil interpretations record: MT0381. Diagnostic horizons and features recognized in this pedon are:
Particle-size control section: The zone from 10 to 32 inches (Bk1, Bk2, Bk3 horizons).
Ochric epipedon: The zone from the soil surface to 3 inches, mixed (A horizon).
Calcic horizon: The zone from 3 to 32 inches ( Bk1, Bk2, Bk3 horizons).
Lithic contact: The contact with limestone bedrock at 32 inches (R layer).
(Jefferson County area pedon #31215.)
Taxonomic version: Eighth Edition, 1998.
Classification changed from Haplocalcidic Ustochrept to Aridic Calciustepts 7/98.
Formatting and classification updated 7/98.