LOCATION COCHETOPA COEstablished Series
TAXONOMIC CLASS: Fine, smectitic Pachic Argicryolls
TYPICAL PEDON: Cochetopa stony loam - grassland. (Colors are for dry soil unless otherwise noted.)
A--0 to 8 inches; dark gray (10YR 4/1) stony loam, black (10YR 2/1) moist; strong fine granular structure; soft, very friable, slightly sticky and slightly plastic; 15 percent stones; neutral (pH 6.8); clear smooth boundary. (4 to 14 inches thick)
BAt--8 to 12 inches; dark gray (10YR 4/1) clay loam, black (10YR 2/1) moist; moderate medium subangular blocky structure parting to fine granular; slightly hard, friable, slightly sticky and slightly plastic; few thin patchy clay films on faces of peds and in root channels and pores; many dark colored mineral grains and fragments of basalt, of sand and silt size; 10 percent stones; neutral (pH 6.8); clear smooth boundary. (4 to 10 inches thick)
Bt1--12 to 20 inches; dark grayish brown (10YR 4/2) stony clay, very dark brown (10YR 2/2) moist; moderate medium subangular blocky structure; slightly hard, very friable, sticky and plastic; thin continuous clay films on faces of peds in root channels and pores; many dark colored mineral grains and fragments of basalt, of sand and silt size; 20 percent stones; neutral (6.8); clear smooth boundary.
Bt2--20 to 32 inches; brown (7.5YR 5/4) stony clay, brown (7.5YR 4/4) moist; moderate medium subangular blocky structure; slightly hard, friable, sticky and plastic; thin continuous clay films on faces of peds and in root channels and pores; many dark colored mineral grains and fragments of basalt, of sand and silt size; 20 percent stones; neutral (pH 7.2); gradual smooth boundary. (The combined thickness of the Bt horizon ranges from 12 to 36 inches)
BCt--32 to 40 inches; brown (7.5YR 5/4) stony sandy clay, brown (7.5YR 4/4) moist; weak medium subangular blocky structure; very hard, friable, sticky and plastic; thin patchy clay films on faces of peds and in root channels and pores; many dark colored mineral grains and fragments of basalt, of sand and silt size; 20 percent stones; slightly alkaline (pH 7.6); gradual smooth boundary. (4 to 12 inches thick)
C--40 to 60 inches; light brown (7.5YR 6/4) stony clay loam, brown (7.5YR 5/4) moist; massive; hard, friable, slightly sticky and slightly plastic; many dark colored mineral grains and fragments of basalt, of sand and silt size; 30 percent stones; slightly alkaline (pH 7.6). (several feet thick)
TYPE LOCATION: Gunnison County, Colorado; East half of Sec. 22, T. 15 S., R. 86 W.
RANGE IN CHARACTERISTICS:
Soil moisture regime: ustic; the moisture control section is dry more than half the time when the soil temperature is above 41 degrees F.
Mean annual soil temperature: 36 to 42 degrees F.
Mean summer soil temperature: 47 to 56 degrees F.
Thickness of the mollic epipedon: 16 to 30 inches
Depth to the base of the argillic horizon: 20 to 60 inches or more
Base saturation: ranges from 60 to 100 percent, but usually is more than 80 percent in most subhorizons
Linear extensibility (estimated): 2.0 to 4.0 cm
Particle size control section (weighted averages):
Clay content: 35 to 55 percent
Rock fragment content: 5 to 35 percent, dominantly stones
A horizon:
Hue: 7.5YR to 2.5Y
Value: 2 to 5 dry, 2 or 3 moist
Chroma: 1 to 3 dry or moist
Texture: L, ST-L
Rock fragments: 0 to 20 percent
Reaction: slightly acid or neutral
Bt horizon:
Hue: 7.5YR to 2.5Y
Value: 3 to 7 dry, 2 to 6 moist
Chroma: 1 to 4, dry or moist
Texture: ST-C, ST-CL
Clay content: 35 to 55 percent
Rock fragments: 5 to 35 percent, dominantly stones
Content of fine and coarser sand: 15 to 35 percent
Reaction: slightly acid or neutral
C horizon (not in all pedons):
Hue: 7.5YR to 2.5Y
Value: 5 or 6 dry, 4 or 5 moist
Chroma: 2 to 4, dry or moist
Texture: ST-L, ST-SCL, ST-CL, ST-C
Clay content: 20 to 50 percent
Rock fragments: 5 to 35 percent, dominantly stones
Reaction: neutral or slightly alkaline
COMPETING SERIES: These are the Bischoff, Burnette, Faim, Friana, Fulcher, Grouseville, Guero, Leemorris, Luna, Mancos, Mayflower, Paulson, Perinos, Richens, Runlett, Skutum, Slights, Sudpeak, Teedown, and Toponce series.
Bischoff: have silty clay loam and silty clay textures in the argillic horizon and have a presumed xeric moisture regime
Burnette, Fulcher, Grouseville, and Paulson: have horizons of secondary calcium carbonate accumulation.
Faim: have a xeric moisture regime.
Friana: have a lithologic discontinuity with cindery materials
Guero: have rock fragments that are dominantly gravel or cobbles in the control section and are dry less than half the time when the soil temperature is above 41 degrees F.
Luna: overlie beds of ash and tuff at depths of less than 40 inches and have significant amount of ash throughout the soil.
Leemorris, Mancos, Mayflower, and Runlett: have a lithic contact at depths of 20 to 40 inches.
Perinos and Richens: have hue redder than 7.5YR in the Bt horizon.
Skutum: have sandy loam textures in the C horizon.
Slights: is an old series last updated in 2/46 and cannot be accurately competed with data available.
Sudpeak: have endosaturation at depths of 3 to 6 feet.
Teedown: are dry less than half the time when the soil temperature is greater than 41 degrees F.
Toponce: have less than 5 percent rock fragments in the argillic horizon and have a presumed xeric moisture regime.
GEOGRAPHIC SETTING:
Parent material: colluvium and slope alluvium derived principally from basalt and rhyolitic tuff
Landform: mountain slopes, hills, and valley sides
Slopes: 5 to 50 percent
Elevation: 7,000 to 10,000 feet
Mean annual temperature: 34 to 42 degrees F.
Mean annual precipitation: 16 to 22 inches, relatively evenly distributed throughout the year.
Frost-free period: 30 to 75 days
GEOGRAPHICALLY ASSOCIATED SOILS: These are the Youman and Passar soils. Youman soils have hue of 5YR or redder and have mollic epipedons less than 16 inches thick. Passar soils have more than 35 percent rock fragments and have mollic epipedons less than 16 inches thick.
DRAINAGE AND PERMEABILITY: Well drained; negligible to very high runoff; slow permeability.
USE AND VEGETATION: These soils are used as livestock grazing, wood products, and for recreational purposes. Native vegetation is mainly big sagebrush, snowberry, Thurber fescue, nodding brome, and mountain bluegrass.
DISTRIBUTION AND EXTENT: Mountainous areas of central Colorado. LRR E, MLRA 48A. The series is of moderate extent.
MLRA SOIL SURVEY REGIONAL OFFICE (MO) RESPONSIBLE: Bozeman, Montana
SERIES ESTABLISHED: Gunnison County, Colorado, 1974.
REMARKS: Diagnostic features recognized in this pedon are:
Mollic epipedon: from 0 to 20 inches (A, BAt, and Bt1 horizons)
Argillic horizon: The zone from 12 to 40 inches (Bt1, Bt2, and BCt horizons)
Particle-size control section; The zone from 12 to 32 inches (Bt1 and Bt2 horizons)
This revision (10/98) limits the range in characteristics to more closely match the original concept of this series. Soils without rock fragments or without stones as the dominant fraction are now excluded. Sandstone and shale are excluded from the parent material. This series was determined to be mainly in the ustic moisture regime; the upper limit of average annual precipitation was reduced from 30 to 22 inches. Soils that border a udic regime (and are typically forested) are now excluded from the series concept.
Keys to Soil Taxonomy: classified according to the 8th edition, 1998.
ADDITIONAL DATA: