LOCATION TOMBAC COEstablished Series
TAXONOMIC CLASS: Fine, smectitic, frigid Typic Paleustolls
TYPICAL PEDON: Tombac loam, on a southwest facing, simple, 6 percent slope in ponderosa pine woodland, at an elevation of 8,600 feet. (Colors are for dry soil unless otherwise noted.) Described on July 22, 1985.
Oe--0 to 1 inch; intermediately decomposed needles and twigs. (0 to 3 inches thick)
A1--1 to 3 inches; very dark grayish brown (10YR 3/2) loam, black (10YR 2/1) moist; weak fine granular structure; hard, friable, slightly sticky and moderately plastic; many very fine roots; many very fine continuous pores; neutral (pH 6.8); clear smooth boundary.
A2--3 to 12 inches; very dark grayish brown (10YR 3/2) loam, black (10YR 2/1) moist; moderate medium subangular blocky structure; hard, friable, moderately sticky and moderately plastic; common very fine roots, few medium and coarse roots; many very fine continuous pores; neutral (pH 6.8); clear smooth boundary. (combined thickness of the A horizons is 10 to 16 inches)
E/B--12 to 16 inches; 60 percent E, pale brown (10YR 6/3) loam, brown (10YR 4/3) moist, and 40 percent B, brown (7.5YR 5/4) clay loam, brown (7.5YR 4/4) moist; moderate medium subangular blocky structure; very hard, firm, moderately sticky and moderately plastic; few very fine, and common fine roots; many very fine continuous pores; few faint clay films on faces of peds of B part; neutral (pH 6.8); gradual wavy boundary. (2 to 8 inches thick)
Bt1--16 to 26 inches; strong brown (7.5YR 5/6) clay, strong brown (7.5YR 4/6) moist; strong medium prismatic structure parting to strong medium angular blocky; extremely hard, extremely firm, very sticky and moderately plastic; few fine, medium, and coarse roots; common very fine continuous pores; many prominent films on faces of peds; neutral (pH 6.8); gradual wavy boundary.
Bt2--26 to 37 inches; reddish yellow (7.5YR 6/6) clay, light brown (7.5YR 6/4) moist; few fine faint strong brown (7.5YR 4/6) lithochromic mottles; strong medium prismatic structure parting to strong medium angular blocky; extremely hard, extremely firm, very sticky and moderately plastic; few coarse roots; few very fine continuous pores; many prominent clay films on faces of peds; neutral (pH 6.8); gradual wavy boundary. (combined thickness of the Bt horizons is 15 to 40 inches)
2C1--37 to 46 inches; light gray (10YR 7/2) clay, pale brown (10YR 6/3) moist; few fine faint strong brown (7.5YR 5/6) lithochromic mottles; massive; extremely hard, extremely firm, very sticky and moderately plastic; neutral (pH 6.8); clear wavy boundary. (6 to 20 inches thick)
2C2--46 to 61 inches; light gray (10YR 7/1) clay, light yellowish brown (10YR 6/4) moist; few fine distinct brownish yellow (10YR 6/6) lithochromic mottles; massive; extremely hard, extremely firm, very sticky and moderately plastic; neutral (pH 6.8).
TYPE LOCATION: Dolores County, Colorado; about 12 miles north of Mancos; located about 1,300 feet east and 1,100 feet north of the southwest corner, sec. 28, T. 38N., R. 13 W.; Stoner USGS quad; lat. 37 degrees 31 minutes 25 seconds N. and long. 108 degrees 18 minutes 04 seconds W., NAD 27
RANGE IN CHARACTERISTICS: (Depths given are measured from the mineral soil surface)
Soil moisture regime: ustic (typic ustic subclass).
Mean annual soil temperature: 42 to 45 degrees F.
Mean summer soil temperature: 60 to 63 degrees F.
Thickness of the mollic epipedon: 10 to 16 inches
Linear Extensibility: 5.0 to 6.0 cm
Particle-size control section:
Clay content: 35 to 55 percent
Rock fragment content: 0 to 15 percent
A horizon:
Value: 3 to 5 dry, 2 or 3 moist
Chroma: 1 or 2, dry and moist
Rock fragment content: 0 to 15 percent
Reaction: slightly acid or neutral
E/B horizon:
E part;
Hue: 7.5YR or 10YR
Value: 5 or 6 dry, 3 or 4 moist
Chroma: 3 or 4, dry and moist
Texture: L
B part:
Hue: 7.5YR or 10YR
Value: 5 or 6 dry, 4 or 5 moist
Chroma: 4 to 6, dry and moist
Texture: CL, C
Reaction: slightly acid or neutral
Bt horizons:
Value: 5 or 6 dry, 4 to 6 moist
Chroma: 4 to 6, dry and moist
Texture: CL, C
Rock fragments: 0 to 15 percent
Reaction: slightly acid or neutral
2C horizon:
Value: 5 to 7 dry, 4 to 6 moist
Chroma: 1 to 4, dry and moist
Texture: CL, C
Clay content: 35 to 55 percent
Rock fragments: 0 to 15 percent
COMPETING SERIES: There are no competing series in this family at the present time. The Maudrey series, in a closely related family, has a mollic epipedon more than 20 inches thick.
GEOGRAPHIC SETTING:
Parent material: slope alluvium over residuum derived from Dakota sandstone and shale.
Landform: mesas.
Slopes: 1 to 15 percent
Elevation: 8,200 to 8,900 feet
Mean annual air temperature: 40 to 43 degrees F.
Mean annual precipitation: 20 to 25 inches.
Wettest months: July and August receive slightly more precipitation than other months.
Driest months: May and June receive the least precipitation, however the soils are still moist from snowmelt.
Frost-free period: 70 to 100 days.
GEOGRAPHICALLY ASSOCIATED SOILS: These are the Behanco, Fughes, and Maudrey soils.
Behanco soils are loamy-skeletal and have a cryic temperature regime and are on mesas at higher elevations.
Fughes soils do not have the E/B horizon and have a thick mollic epipedon and are in drainageways and on hills.
Maudrey soils have a thick mollic epipedon and the top of the argillic horizon is deeper than 24 inches, and are on mesas.
DRAINAGE AND PERMEABILITY: Well drained; slow permeability; low runoff.
USE AND VEGETATION: Used mainly for timber production, livestock grazing, and wildlife habitat. The native vegetation is ponderosa pine, Gambel's oak, mountain snowberry, serviceberry, mountain brome, western wheatgrass, Parry's danthonia, needlegrass, quaking aspen, muttongrass, and sedge.
DISTRIBUTION AND EXTENT: Southwestern Colorado. LRR E, MLRA 48A. The series is of small extent.
MLRA SOIL SURVEY REGIONAL OFFICE (MO) RESPONSIBLE: Bozeman, Montana.
SERIES PROPOSED: Dolores County, Animas-Dolores Area, Colorado. 1997.
REMARKS: Diagnostic horizons and features recognized in this pedon are:
Mollic epipedon: The zone from 1 to 12 inches. (A1 and A2 horizons).
Argillic horizon: The zone from 16 to 37 inches. (Bt1 and Bt2 horizons).
Pale- feature: Clay content of the argillic horizon does not decrease significantly with depth, and chroma is 6 (moist or dry) throughout the argillic (Bt1 and Bt2 horizons).
Particle size control section: The zone from 16 to 36 inches (the Bt1, and part of the Bt2 horizon).
Keys to Soil Taxonomy: Classified according to the Eighth Edition, 1998