LOCATION SANPEDRO COEstablished Series
TAXONOMIC CLASS: Loamy-skeletal, mixed, superactive, frigid Aridic Lithic Argiustolls
TYPICAL PEDON: Sanpedro very cobbly silt loam, 9 to 65 percent slopes in rangeland. (Colors are for dry soil unless otherwise noted.)
A--0 to 5 centimeters; brown (7.5YR 4/3) very cobbly silt loam, very dark brown (7.5YR 2.5/2) moist; 15 percent clay; weak fine granular structure; friable, soft, slightly sticky, slightly plastic; common very fine and common medium roots throughout; common very fine irregular pores; 20 percent gravel and 20 percent cobbles; noneffervescent; slightly alkaline (pH 7.4); clear smooth boundary.
Bt--5 to 18 centimeters; brown (7.5YR 4/3) very cobbly silt loam, dark brown (7.5YR 3/3) moist; 20 percent clay; moderate fine subangular blocky structure; friable, slightly hard, moderately sticky, moderately plastic; common very fine and medium roots throughout; common very fine dendritic tubular pores; many clay films on faces of peds; 25 percent gravel and 25 percent cobbles; noneffervescent; slightly alkaline (pH 7.4); clear wavy boundary.
Btk--18 to 28 centimeters; brown (7.5YR 4/3) extremely cobbly silt loam, dark brown (7.5YR 3/3) moist; 20 percent clay; moderate fine subangular blocky structure; friable, slightly hard, moderately sticky, moderately plastic; common very fine and medium roots throughout; common very fine dendritic tubular pores; many distinct clay films on faces of peds; few fine carbonate masses in matrix; 30 percent gravel and 30 percent cobbles; slightly effervescent (25 percent calcium carbonate equivalent); slightly alkaline (pH 7.6); clear wavy boundary.
Bk--28 to 43 centimeters; brown (7.5YR 4/3) extremely cobbly loam, dark brown (7.5YR 3/3) moist; 16 percent clay; weak fine subangular blocky structure; friable, soft, slightly sticky, slightly plastic; common very fine and medium roots throughout; common very fine dendritic tubular pores; many medium carbonate masses in matrix; 35 percent gravel and 35 percent cobbles; strongly effervescent (50 percent calcium carbonate equivalent); moderately alkaline (ph 8.0); abrupt irregular boundary.
R--43 centimeters; fractured basalt.
TYPE LOCATION: Costilla County, Colorado; Sanchez Res USGS topographic quadrangle, NAD83; 37 degrees 2 minutes 2.34 seconds north latitude and 105 degrees 27 minutes 58.92 seconds west longitude; UTM 458,523 meters E, 4098,744 meters N, zone 13.
RANGE IN CHARACTERISTICS:
Soil moisture:
Soil moisture regime subclass: aridic (torric)
Soil moisture regime class: ustic
Mean annual soil temperature: 41 to 46 degrees F (5 to 7.8 degrees C)
Mean summer soil temperature: 63 to 66 degrees F (17.2 to 18.9 degrees C)
Depth to restrictive feature: 10 to 20 inches (25 to 51 centimeters) to bedrock, lithic
Depth to argillic horizon: 2 to 4 inches (5 to 10 centimeters)
Depth to calcic horizon: 6 to 13 inches (15 to 33 centimeters)
Depth to lithic contact: 10 to 20 inches (25 to 51 centimeters) to lithic contact
Thickness of mollic epipedon: 2 to 4 inches (5 to 10 centimeters)
Thickness of argillic horizon: 4 to 10 inches (10 to 25 centimeters)
Thickness of calcic horizon: 0 to 6 inches (0 to 15 centimeters)
Surface fragments: 30 to 50 percent subangular indurated basalt gravel and 5 to 10 percent subangular indurated basalt cobbles
Particle-size control section (weighted average):
Clay content: 22 to 35 percent
Sand content: 25 to 52 percent
Rock fragments: 20 to 35 percent basalt gravel, 15 to 25 percent cobbles
A horizon(s)
Hue: 7.5YR and 10YR
Value: 3 or 4 dry; 2 or 3 moist
Chroma: 2 or 3
Texture: very cobbly silt loam
Clay content: 12 to 22 percent
Carbonate clay content: 0 to 1 percent
Sand content: 20 to 40 percent
Silt content: 40 to 70 percent
Fragment content, total: 35 to 60 percent
Fragment size and content: 20 to 35 percent indurated basalt gravel
15 to 25 percent indurated basalt cobbles
Calcium carbonate equivalent: 0 to 1 percent
Electrical conductivity: 0 to 2 mmhos/cm
Reaction: pH 6.6 to 7.8
Organic matter content: 2.0 to 10.0 percent
Bt horizon(s)
Hue: 7.5YR and 10YR
Value: 4 or 5 dry; 2 or 3 moist
Chroma: 2 or 3
Texture: very cobbly silt loam, very cobbly loam
Clay content: 18 to 35 percent
Carbonate clay content: 0 to 2 percent
Sand content: 25 to 52 percent
Silt content: 40 to 65 percent
Fragment content, total: 35 to 60 percent
Fragment size and content: 20 to 35 percent indurated basalt gravel
15 to 25 percent indurated basalt cobbles
Calcium carbonate equivalent: 0 to 5 percent
Electrical conductivity: 0 to 2 mmhos/cm
Reaction: pH 6.6 to 7.8
Organic matter content: 1.5 to 3.0 percent
Btk horizon(s)
Hue: 7.5YR and 10YR
Value: 4 or 5 dry; 3 or 4 moist
Chroma: 2 or 3
Texture: extremely cobbly silt loam, very cobbly silt loam, extremely cobbly loam
Clay content: 18 to 35 percent
Carbonate clay content: 1 to 5 percent
Sand content: 25 to 52 percent
Silt content: 40 to 65 percent
Fragment content, total: 35 to 75 percent
Fragment size and content: 20 to 50 percent indurated basalt gravel
15 to 40 percent indurated basalt cobbles
Calcium carbonate equivalent: 15 to 40 percent
Electrical conductivity: 0 to 2 mmhos/cm
Reaction: pH 6.6 to 7.8[j1]
Organic matter content: 1.2 to 2.0 percent
Bk horizon(s)
Hue: 7.5YR and 10YR
Value: 4 to 6 dry; 3 to 5 moist
Chroma: 2 or 3
Texture: extremely cobbly loam, very cobbly sandy loam
Clay content: 10 to 22 percent
Carbonate clay content: 1 to 7 percent
Sand content: 40 to 52 percent
Silt content: 28 to 60 percent
Fragment content, total: 35 to 75 percent
Fragment size and content: 20 to 50 percent indurated basalt gravel
15 to 40 percent indurated basalt cobbles
Calcium carbonate equivalent: 20 to 55 percent
Electrical conductivity: 0 to 2 mmhos/cm
Reaction: pH 7.9 to 8.4
Organic matter content: 1.0 to 1.5 percent
R horizon(s); fractured basalt
COMPETING SERIES:
Fletcherpeak soils: have limestone rock fragments.
Wheelerpass soils: non-calcareous throughout the profile.
GEOGRAPHIC SETTING:
Parent material: Loamy slope alluvium over residuum derived from basalt
Landform: mesas and scarps
Slopes: 3 to 65 percent
Elevation: 7,700 to 9,100 feet
Mean annual air temperature: 37 to 41 degrees F (3.0 to 5.0 degrees C)
Mean annual precipitation: 12 to 16 inches (305 to 406 millimeters)
Seasonal pattern: The soil moisture control section is affected by snow melt in early spring and peak precipitation occurring in the form of thunderstorms from June to September.
Frost-free period: 75 to 90 days.
GEOGRAPHICALLY ASSOCIATED SOILS: This is the
Potrio series.
The Potrio soils are deep to basalt bedrock.
DRAINAGE AND PERMEABILITY: Well drained, high runoff, moderately permeability.
USE AND VEGETATION: These soils are used principally for livestock grazing. Typical vegetation is two needle pinyon, Rocky Mountain juniper, Douglas-fir, Wyoming big sagebrush, currant and lupine.
DISTRIBUTION AND EXTENT: Located in the San Luis Valley area on Basalt mesas in south central Colorado. LLR E, MLRA 51. The series is of moderate extent.
MLRA SOIL SURVEY REGIONAL OFFICE (MO) RESPONSIBLE: Bozeman, Montana
SERIES ESTABLISHED: Costilla County, Colorado, 2009
REMARKS:
Diagnostic horizons and features recognized in this pedon are:
Particle-size control section: The zone from 2 to 11 inches (5 to 28 centimeters) Bt, Btk horizons.
Argillic horizon: The zone from 2 to 11 inches (5 to 28 centimeters) Bt, Btk horizons.
Calcic horizon: The zone from 7 to 17 inches (18 to 43 centimeters) Btk, Bk horizons.
Lithic contact: 17 inches (43 centimeters) R horizon
The assignment of the Cation-exchange activity class is inferred from lab data from similar soils in the surrounding area.
Taxonomic Version: Tenth edition, 2006