LOCATION BIGTOE AZEstablished Series
TAXONOMIC CLASS: Loamy-skeletal, mixed, superactive, thermic, shallow Ustic Haplodurids
TYPICAL PEDON: Bigtoe gravelly sandy loam - rangeland. (Colors are for dry soil unless otherwise noted.) The soil surface is covered with 75 percent gravel.
A--0 to 1 inch; brown (10YR 5/3) gravelly sandy loam, dark brown (10YR 3/3) moist; moderate fine and medium granular structure; soft, very friable, slightly sticky and slightly plastic; many very fine and fine roots; many very fine and fine pores; 25 percent gravel; violently effervescent; moderately alkaline (pH 8.0); clear wavy boundary. (1 to 3 inches thick)
Bk1--1 to 5 inches; pale brown (10YR 6/3) very gravelly sandy clay loam, dark brown (10YR 3/3) moist; moderate fine and medium subangular blocky structure; soft, very friable, moderately sticky and moderately plastic; many very fine, fine, and few medium roots; many very fine and fine pores; common coarse carbonate masses and common carbonate coatings on bottom of rock fragments; 43 percent gravel and 7 percent cobble; violently effervescent; 24 percent calcium carbonate equivalent; moderately alkaline (pH 8.4); clear wavy boundary. (3 to 10 inches thick)
Bk2--5 to 17 inches; 10 percent white (10YR 8/1) and 90 percent light gray (10YR 7/2) very gravelly sandy loam, brown (10YR 5/3) moist; massive; soft, very friable, slightly sticky and nonplastic; many very fine, fine, and few medium roots; many very fine and fine pores; many extremely coarse carbonate concretions; 43 percent gravel and 7 percent cobble; violently effervescent; 31 percent calcium carbonate equivalent; moderately alkaline (pH 8.4); abrupt wavy boundary. (5 to 15 inches thick)
Bkqm--17 to 20 inches; silica and carbonate-cemented hardpan; very hard; upper 1/8 to 1/2 inch is laminar.
TYPE LOCATION: Graham County, Arizona; on the San Carlos Indian Reservation, approximately 5 miles southwest of Geronimo. 1,850 feet south and 1,775 feet east of the northwest corner of sec. 5, T. 5 S., R. 22 E. Latitude 33 degrees, 1 minute, 46.41 seconds N; longitude 110 degrees, 6 minutes, 54.46 seconds W; NAD 83; Topographic quadrangle: Geronimo, Arizona.
RANGE IN CHARACTERISTICS:
Soil moisture: Intermittently moist in some part of the soil moisture control section during December through April and July through September. Driest during May and June. Ustic aridic soil moisture regime.
Soil temperature: 60 to 68 degrees F.
Depth to calcic horizon: 1 to 10 inches
Depth to duripan: 5 to 20 inches
Rock fragments: 35 to 75 percent in the particle size control section
Clay content: 15 to 27 percent in the particle size control section
Reaction (pH): slightly alkaline to moderately alkaline (7.4 to 8.4)
A horizon
Hue: 7.5YR, 10YR
Value: 4 through 6 dry, 3 through 5 moist
Chroma: 2 through 4, dry or moist
Bk horizon
Hue: 7.5YR, 10YR
Value: 5 through 8 dry, 3 through 5 moist
Chroma: 2 through 4, dry or moist
Texture: sandy loam, sandy clay loam
The Bkqm horizon is continuously cemented except for occasional cracks.
The A and B horizons do not meet the moisture requirements for a mollic epipedon.
COMPETING SERIES: This is the Bartmus (AZ) series. Bartmus soils do not have a calcic horizon above the duripan and have a lithic contact below the duripan.
GEOGRAPHIC SETTING: These soils are on fan terraces. Elevations range from 2,800 to 4,500 feet. Slopes range from 3 to 20 percent. The soils formed in very gravelly alluvium derived from mixed igneous and sedimentary sources. The mean annual air temperature ranges from 57 degrees F. to 65 degrees F. Mean annual precipitation ranges from about 12 to 16 inches with a slight winter maximum. Frost-free period is 180 to 230 days.
GEOGRAPHICALLY ASSOCIATED SOILS: These are the Tombstone and Ryallen soils. These soils are very deep and do not have duripans.
DRAINAGE AND PERMEABILITY: Well drained; medium to rapid runoff; moderate permeability.
USE AND VEGETATION: Used for livestock grazing and wildlife habitat. Vegetation is mainly creosotebush, yucca, opuntia spp., bush muhly, six week grama, snakeweed, whitethorn, globe mallow, Blackfoot daisy, fluffgrass, chinchweed, spurge, Texas filaree, Honeymat, purple threeawn, pigweed and occasional mesquite.
DISTRIBUTION AND EXTENT: Southern Arizona. It is of limited extent. MLRA is 38.
MLRA SOIL SURVEY REGIONAL OFFICE (MO) RESPONSIBLE: Phoenix, Arizona
SERIES ESTABLISHED: Soil Survey of San Carlos Indian Reservation, Arizona, Parts of Gila and Graham Counties (AZ675), 2009.
REMARKS: Diagnostic horizons and features recognized in this pedon are:
Ochric epipedon - the zone from 0 to 1 inch (A horizon)
Calcic horizon - the zone from 1 to 17 inches (Bk1 and Bk2 horizons)
Duripan- the zone starting at 17 inches (Bkqm horizon)
Classified according Soil Taxonomy, Second Edition, 1999; Keys to Soil Taxonomy, Tenth Edition, 2006.