LOCATION ZAU COEstablished Series
TAXONOMIC CLASS: Fine, smectitic, frigid Typic Argiustolls
TYPICAL PEDON: Zau stony loam, rangeland. (Colors are for dry soil unless otherwise noted.)
Oi--0 to 2 inches; organic material consisting of leaves and bark.
Oe--2 to 4 inches; organic material consisting of partly decomposed plant material.
A1--4 to 12 inches; dark grayish brown (10YR 4/2) stony loam, very dark grayish brown (10YR 3/2) moist; weak fine granular structure; soft, friable; many medium and fine roots; few pores; 2 percent stones and cobble; 5 percent pebbles; neutral (pH 7.2); clear smooth boundary. (6 to 12 inches thick)
A2--12 to 17 inches; brown (10YR 4/3) clay loam, dark brown (10YR 3/3) moist; moderate medium granular structure; slightly hard, friable, slightly sticky, slightly plastic; many medium and fine roots; few pores; 5 percent pebbles; neutral (pH 7.2); gradual wavy boundary. (0 to 6 inches thick)
Bt1--17 to 21 inches; brown (10YR 5/3) in matrix and light yellowish brown (10YR 6/4) clay loam, brown (10YR 4/3) in matrix moist and yellowish brown (10YR 5/4) moist; moderate medium subangular blocky structure parting to moderate medium granular; hard, firm, slightly sticky and slightly plastic; many prominent clay films on faces of peds; few fine roots; few, fine discontinuous pores; 5 percent pebbles; neutral (pH 7.0); gradual wavy boundary. (4 to 12 inches thick)
Bt2--21 to 31 inches; brown (10YR 5/3) in matrix and brownish yellow (10YR 6/6) clay, brown (10YR 4/3) moist in matrix and brownish yellow (10YR 6/6) moist; moderate medium prismatic structure parting to moderate medium subangular blocky; hard, firm, very sticky and plastic; many prominent clay films on faces of peds; few, very fine roots; few, very fine pores; 5 percent pebbles; neutral (pH 6.8); clear smooth boundary. (6 to 16 inches thick)
C--31 to 36 inches; brown (10YR 5/3) in matrix and brownish yellow (10YR 6/6) clay loam, brown (10YR 4/3) moist in matrix and brownish yellow (10YR 6/6) moist; massive; slightly hard, friable, sticky and plastic; few, very fine roots; 15 percent pebbles; neutral (pH 7.2); clear smooth boundary. (0 to 12 inches thick)
Cr--36 inches; weathered sandstone and shale
TYPE LOCATION: La Plata County, Colorado; 175 feet east and 190 feet south of the NW corner of section 22, T. 35 N., R. 11 W. U.S.G.S. Hesperus quad.; Lat. 37 degrees, 16 minutes, 56 seconds N., and Long. 108 degrees, 03 minutes, 48 seconds W. NAD27
RANGE IN CHARACTERISTICS:
(Depths given are measured from the mineral soil surface)
Mean annual soil temperature: 42 to 47 degrees F.
Mean summer soil temperature: 53 to 57 degrees F.
Depth to paralithic contact: 20 to 40 inches to weathered sandstone and shale
Thickness of the mollic epipedon: 7 to 16 inches
Rock fragments: 5 to 35 percent throughout the solum and C horizon.
A horizon:
Hue: 7.5YR through 2.5Y
Value: 3 to 5 dry, 2 or 3 moist
Chroma: 2 or 3 dry or moist
Reaction: neutral or slightly alkaline
Bt horizon:
Hue: 7.5YR through 2.5Y
Value: 5 or 6, 4 through 6 moist
Chroma: 3 through 6 (Colors are commonly variegated due to the nature of the parent material.)
Texture: clay loam or clay and has 35 to 45 percent clay, 35 to 50 percent silt, and 10 to 55 percent sand
Reaction: slightly acid or neutral
C horizon:
Hue: 7.5YR through 2.5Y
Texture: clay loam or sandy clay loam
Reaction: slightly acid to slightly alkaline
Clay films are in the fractures of paralithic material in some pedons.
COMPETING SERIES: These are the Absarokee, Acree, Barela, Capillo, Delson, Ekah, Herm, Morapos, Moreno, Nortez, Pramiss, Ricot, Tamaneen, Tukuhnik, and Work series.
Absarokee,
Barela, Nortez: have lithic contacts
Acree,
Delson,
Ekah,
Herm,
Morapos,
Ricot,
Tamaneen,
Tukuhnik, Work: do not have a lithic or paralithic contact above 60 inches
Capillo: paralithic contact between 40 and 60 inches deep
Pramiss: has zones of secondary calcium carbonate accumulation
GEOGRAPHIC SETTING:
Parent material: colluvium and residuum derived from sandstone and shale
Landform: hills, mesas, plateaus, mountains, cuestas, and structural benches
Elevation: 7,500 to 9,000 feet
Slope: 3 to 25 percent
Mean annual precipitation: 16to 22 inches
Mean annual temperature: 40 to 45 degrees F
Frost-free season: 75 to 110 days
GEOGRAPHICALLY ASSOCIATED SOILS: These are the Archuleta and Sanchez soils which are shallow over bedrock and the Herm soils that lack bedrock within 40 inches.
DRAINAGE AND PERMEABILITY: Well drained; high or very high runoff; slow permeability.
USE AND VEGETATION: These soils are used for pasture and wildlife habitat. Native vegetation is mainly Gambel's oak, snowberry, Oregon grape, bluegrass, Arizona fescue, sedges, needleandthread, western wheatgrass, Lupine, and larkspur.
DISTRIBUTION AND EXTENT: Southwest Colorado. LRR-E, MLRA 48A. The soils are of moderate extent.
MLRA SOIL SURVEY REGIONAL OFFICE (MO) RESPONSIBLE: Bozeman, Montana
SERIES ESTABLISHED: La Plata County Area, Colorado, 1982.
REMARKS:
Diagnostic horizons and features recognized in this pedon are:
Particle-size control section: the zone from 17 to 31 inches (Bt1 and Bt2 horizons)
Argillic horizon: the zone from 17 to 31 inches (Bt1 and Bt2 horizons)
Paralithic contact: the contact with weathered sandstone and shale at 36 inches (Cr layer)
Soil Taxonomy Second Edition, 1999