LOCATION GACHADO AZEstablished Series
TAXONOMIC CLASS: Loamy-skeletal, mixed, superactive, hyperthermic Lithic Haplargids
TYPICAL PEDON: Gachado extremely cobbly loam - rangeland. (Colors are for dry soils unless otherwise noted.) 70 to 80 percent of the surface covered with basalt cobble and gravel.
A--0 to 2 inches; brown (7.5YR 5/4) extremely cobbly loam, brown (7.5YR 4/4) moist; weak medium platy structure; slightly hard, friable, slightly sticky and slightly plastic; few very fine roots; common fine vesicular pores; 80 percent basalt cobble and gravel; moderately alkaline (pH 8.0); abrupt wavy boundary. (1 to 3 inches thick)
Bt1--2 to 4 inches; yellowish red (5YR 5/6) gravelly sandy clay loam, yellowish red (5YR 4/6) moist; moderate fine and medium subangular blocky structure; hard, very friable, slightly sticky and slightly plastic; few very fine and fine roots; few very fine tubular and common fine irregular pores; few faint clay films on faces of peds; 20 percent basalt gravel; moderately alkaline (pH 8.0); clear wavy boundary. (2 to 4 inches thick)
Bt2--4 to 8 inches; yellowish red (5YR 4/6) clay loam, yellowish red (5YR 4/6) moist; moderate medium prismatic structure parting to moderate medium subangular blocky; hard, friable, moderately sticky and moderately plastic; few very fine and fine roots; few very fine tubular pores; few faint clay films on faces of peds; 10 percent basalt gravel; slightly effervescent; moderately alkaline (pH 8.0); clear wavy boundary. (3 to 7 inches thick)
Bt3--8 to 13 inches; yellowish red (5YR 5/6) extremely gravelly sandy clay loam, yellowish red (5YR 4/6) moist; weak medium and coarse subangular blocky structure; hard, very friable, slightly sticky and slightly plastic; few very fine roots; common fine irregular and few fine tubular pores; 65 percent basalt gravel; strongly effervescent; moderately alkaline (pH 8.3); abrupt irregular boundary. (3 to 6 inches thick)
2R--13 inches; andesite, with thin calcium carbonate coatings on bedrock surface.
TYPE LOCATION: Pima County, Arizona; east of Highway 85, Organ Pipe Cactus National Monument; .3 miles east of the southwest corner of section 32, T. 16 S., R. 5 W. Latitude of 31 degrees, 58 minutes, 58 seconds N., Longitude of 112 degrees, 48 minutes, 24 seconds W., NAD 83.
RANGE IN CHARACTERISTICS:
Soil moisture - Intermittently moist in some part of the soil moisture control section during July-September and December-February. Driest during May and June. Typic aridic soil moisture regime.
Rock fragments - averages more than 35 percent in the control section
Depth to bedrock - 7 to 20 inches
Calcium Carbonate - disseminated in the lower part; occurs as filaments or as a thin weakly cemented layer immediately above the bedrock in some pedons
A horizon
Hue: 7.5YR, 5YR
Value: 5, 6 or 7 dry, 3, 4 or 5 moist
Chroma: 3, 4 or 6, dry or moist
Organic matter: less than 1 percent
B horizon
Hue: 7.5YR, 5YR, 2.5YR
Value: 4, 5, 6 or 7 dry, 3, 4 or 5 moist
Chroma: 4, 6 or 8, dry or moist
Texture: clay loam, sandy clay loam, loam
Rock fragments: 10 to 30 percent gravel in the upper horizons and 60 to 70 percent in the lower horizons.
COMPETING SERIES: These are the Marbolite (T)(CA), Vaiva (AZ), and Whipple (T)(CA) series. Vaiva soils have a paralithic contact. Whipple soils are moist in some part of the soil moisture control section for less than 20 days cumulative between July and September and have rock fragments of granite. Marbolite soils do not have an OSD and cannot be competed.
GEOGRAPHIC SETTING: Gachado soils are on mountains and hills. Slopes range from 0 to 55 percent. Elevations are 600 to 3000 feet. The soils formed in alluvium from andesite, latite, rhyolite, basalt, schist and tuff. Mean annual precipitation is 2 to 10 inches and falls mainly as thunderstorms in July-September, and as gentle rains during January and February. Mean annual air temperature is 70 to 76 degrees F. Frost-free period is 250 to 325 days.
GEOGRAPHICALLY ASSOCIATED SOILS: These are the Ajo, Cherioni, Cristobal, Cipriano, and Ligurta soils. Ajo soils have a petrocalcic horizon at a depth of 20 to 40 inches. Cherioni and Cipriano soils do not have argillic horizons. Cristobal and Ligurta soils are very deep.
DRAINAGE AND PERMEABILITY: Well drained; medium runoff; moderately slow permeability.
USE AND VEGETATION: Used for livestock grazing. Vegetation is creosotebush, littleleaf paloverde, Mormon-tea, big galleta, brittlebush, fourwing saltbush, range ratany, black grama, sand dropseed, Arizona cottontop, slender tridens, desert needle grass, bush muhly, saguaro, staghorn cholla, ironwood, ocotillo, jojoba and barrel cactus.
DISTRIBUTION AND EXTENT: Southern Arizona. Gachado soils are moderately extensive. MLRA is 40.
MLRA SOIL SURVEY REGIONAL OFFICE (MO) RESPONSIBLE: Phoenix, Arizona
SERIES ESTABLISHED: Pima County (Organ Pipe Cactus National Monument Survey Area), Arizona; 1971.
REMARKS: Diagnostic horizons and features recognized in this pedon are:
Ochric epipedon - the zone from 0 to 2 inches (A horizon)
Argillic horizon - the zone from 2 to 8 inches (Bt1, Bt2 horizons)
Lithic contact - the boundary at 13 inches (2R horizon)
Classified according to Soil Taxonomy, Second Edition, 1999; Keys to Soil Taxonomy, Tenth Edition, 2006.
Revised for the correlation of AZ661, 12/2008, WWJ