LOCATION BIGPAW AZ+NMEstablished Series
TAXONOMIC CLASS: Fine-silty, mixed, superactive, frigid Pachic Argiustolls
TYPICAL PEDON: Bigpaw loam -- on a plane toeslope sloping 9 percent to the northeast at 8,880 feet elevation -- rangeland. (Colors are for dry soil unless otherwise noted. When described, the soil was dry from 0 to 36 inches and moist below 36 inches.)
A--0 to 5 inches; brown (7.5YR 4/2) loam, very dark brown (7.5YR 2/2) moist; moderate thick platy structure parting to weak medium granular; soft, very friable, slightly sticky and nonplastic; few fine and many very fine roots; common very fine irregularly shaped pores; slightly acid (pH 6.4); clear smooth boundary. (3 to 10 inches thick)
Bt1--5 to 14 inches; dark reddish brown (5YR 3/2) loam, very dark gray (5YR 3/1) moist; weak medium prismatic structure parting to moderate coarse subangular blocky; slightly hard, friable, slightly sticky and slightly plastic; few medium, and common fine and very fine roots; few fine and common very fine tubular pores; common faint clay films on faces of peds and lining pores; neutral (pH 6.6); gradual smooth boundary. (6 to 9 inches thick)
Bt2--14 to 36 inches; dark reddish brown (5YR 3/2) loam, very dark gray (5YR 3/1) moist; moderate medium prismatic structure parting to weak coarse subangular blocky; hard, friable, slightly sticky and slightly plastic; few medium, few fine, and common very fine roots; common fine and common very fine tubular pores; few distinct and common faint clay films on faces of peds and lining pores; neutral (pH 6.6); gradual wavy boundary. (11 to 24 inches thick)
Bt3--36 to 48 inches; dark reddish gray (5YR 4/2) loam, dark reddish brown (5YR 3/2) moist; weak medium prismatic structure parting to moderate medium subangular blocky; hard, friable, slightly sticky and slightly plastic; few fine and common very fine roots; few fine and common very fine tubular pores; few distinct and common faint clay films on faces of peds and lining pores; 5 percent gravel; neutral (pH 6.6); abrupt wavy boundary. (0 to 22 inches thick)
2Btb1--48 to 57 inches; reddish brown (5YR 5/4) and reddish brown (5YR 4/4) stony sandy clay loam, reddish brown (5YR 4/4) and dark reddish brown (5YR 3/2) moist; weak medium prismatic structure parting to moderate coarse subangular blocky; hard, friable, slightly sticky and slightly plastic; few fine and few very fine roots; few fine and many very fine tubular pores; few distinct and common faint clay films on faces of peds and on rock fragments; 15 percent stones, 5 percent cobble, and 10 percent gravel; neutral (pH 6.8); clear wavy boundary. (9 to 22 inches thick)
2Btb2--57 to 65 inches; light brown (7.5YR 6/4) stratified gravelly fine sandy loam, brown (7.5YR 5/4) moist; moderate medium subangular blocky structure; slightly hard, friable, slightly sticky and slightly plastic; few fine and few very fine roots; few fine and common very fine tubular pores; common faint clay films on faces of peds and on rock fragments; 20 percent gravel, 5 percent cobble, and 5 percent stones; neutral (pH 6.8).
TYPE LOCATION: Apache County, Arizona; on the Navajo Indian Reservation about 9 miles southwest of Teec Nos Pos; 900 feet south and 925 feet west of the northeast corner of section 12, T.39 N., R.29 E; Latitude 36 degrees 48 minutes 26 seconds North and Longitude 109 degrees 10 minutes 40 seconds West.
RANGE IN CHARACTERISTICS:
Soil moisture - The soil moisture control section is moist in all parts from January to May and intermittently moist in some part from June to December. Moist in all parts greater than 40 percent of the time (cumulative), when the soil temperature at 20 inches is 41 degrees F or higher. Typic ustic soil moisture regime.
Soil temperature - 44 to 47 degrees F.
Mean summer soil temperature - 59 to 62 degrees F.
Reaction - slightly acid or neutral
Clay content - control section weighted average is 18 to 27 percent
Depth to base of Mollic epipedon - 33 to 52 inches
Organic carbon content - 0.6 to 2.4 percent in Mollic epipedon
A horizon
Hue: 5YR, 7.5YR
Value: 3 or 4 dry, 2 or 3 moist
Chroma: 1 or 2, dry or moist
Bt horizons
Hue: 5YR, 7.5YR
Value: 3 or 4 dry, 2 or 3 moist
Chroma: 1 or 2, dry or moist
Rock fragments: 0 to 5 percent gravel
2Btb1 horizon
Hue: 5YR, 7.5YR
Value: 4 or 5 dry, 3 or 4 moist
Chroma: 2 through 6, dry or moist
Rock fragments: 5 to 30 percent
5 to 10 percent gravel
0 to 5 percent cobble
0 to 15 percent stones
2Btb2 horizon
Hue: 5YR, 7.5YR
Value: 5 or 6 dry, 4 or 5 moist
Chroma: 4 through 6, dry or moist
Texture: stratified fine sandy loam to sandy clay loam
Rock fragments: 10 to 35 percent
10 to 20 percent gravel
0 to 10 percent cobble
0 to 5 percent stones
Other features: some pedons have few, fine, distinct or prominent, 7.5YR, relict redox concentrations.
COMPETING SERIES: These are the Jekley and Owlspring series. Jekley soils are moderately deep to shale. Owlspring soils are somewhat poorly drained and formed in materials derived from basalt and basaltic tuff.
GEOGRAPHIC SETTING: Bigpaw soils are on toeslopes below domes of mountain summits. They formed in eolian material and alluvium derived from Triassic and Jurassic sandstone and siltstone, and Tertiary quartz diorite. Slopes are 5 to 15 percent. Elevation ranges from 8,500 to 9,400 feet. The mean annual precipitation is 18 to 20 inches with more than 50 percent falling as snow from winter storms. The mean annual air temperature is 42 to 45 degrees F. The frost-free period is 80 to 100 days.
GEOGRAPHICALLY ASSOCIATED SOILS: These are the Ligai, Pastorpeak, and Zibetod soils. Ligai soils are loamy-skeletal and occur on warm backslopes of mountains. Pastorpeak soils are loamy-skeletal and occur on north-facing backslopes of mountains. Zibetod soils are loamy-skeletal, shallow, and occur on adjacent footslopes and shoulders of domes.
DRAINAGE AND PERMEABILITY: Well drained; medium runoff; moderate permeability.
USE AND VEGETATION: Bigpaw soils are used for livestock grazing. Present vegetation is muttongrass, western wheatgrass, bottlebrush squirreltail, and black sagebrush, with scattered common chokecherry and Gambel oak.
DISTRIBUTION AND EXTENT: Bigpaw soils are of small extent on the Carrizo Mountains portion of the Colorado Plateau province in northeast Arizona. LRR-D; MLRA 39.
MLRA SOIL SURVEY REGIONAL OFFICE (MO) RESPONSIBLE: Phoenix, Arizona
SERIES ESTABLISHED: Shiprock Area, Parts of San Juan County, New Mexico and Apache County, Arizona; 1993.
REMARKS: Diagnostic horizons and features recognized in this pedon are:
Mollic epipedon - The zone from 0 to 48 inches (A, Bt1, Bt2, Bt3 horizons)
Pachic subgroup - The presence of a mollic epipedon that is greater than 16 inches thick
Argillic horizon - The zone from 5 to 48 inches (Bt1, Bt2, Bt3 horizons)
Lithologic discontinuity - The presence of a buried paleosol at 48 to more than 65 inches (2Btb1 and 2Btb2 horizons)
Keys to Soil Taxonomy - Soils classified according to the Ninth Edition, 2003.
ADDITIONAL DATA: Organic carbon values determined for one horizon from the type location by Inter-Mountain Laboratories, Inc. The particle-size control sections of three pedons, including the type location, were wet sieved to determine percent of size fraction larger than very fine sand (less than 0.1mm). The weighted averages of the three pedons ranged from 4 to 7 percent coarser than very fine sand.