LOCATION CARACARA AZEstablished Series
TAXONOMIC CLASS: Clayey-skeletal, mixed, superactive, thermic Argic Petrocalcids
TYPICAL PEDON: Caracara extremely gravelly sandy loam - rangeland. (Colors are for dry soil unless otherwise noted.)
A--0 to 1 inch; brown (7.5YR 4/4) extremely gravelly sandy loam, very dark grayish brown (10YR 3/2) moist; weak thin platy structure; soft, very friable, nonsticky and nonplastic; common very fine and fine roots; common very fine and fine interstitial and tubular pores; 65 percent gravel; slightly effervescent; slightly alkaline (pH 7.4); abrupt smooth boundary. (1 to 5 inches thick)
Bt--1 to 9 inches; reddish brown (5YR 4/4) cobbly sandy clay loam, reddish brown (5YR 4/4) moist; strong medium subangular blocky structure; slightly hard, friable, sticky and plastic; common very fine and fine roots; common very fine and fine tubular pores; many distinct reddish brown (5YR 4/4) continuous clay films on rock fragments; 20 percent cobble and 10 percent gravel; slightly effervescent; slightly alkaline (pH 7.8); clear wavy boundary. (5 to 10 inches thick)
Btk--9 to 19 inches; reddish brown (5YR 4/4) extremely gravelly clay, yellowish red (5YR 4/6) moist; strong fine subangular blocky structure; slightly hard, friable, very sticky and very plastic; common very fine and fine roots; common very fine and fine tubular pores; many distinct continuous clay films and calcium carbonate coatings on rock fragments; 5 percent cobble and 65 percent gravel; strongly effervescent; moderately alkaline (pH 8.0); abrupt wavy boundary. (5 to 15 inches thick)
Bk--19 to 32 inches; mixed light brown (7.5YR 6/4) and white (7.5YR 8/1) very gravelly sandy clay loam, yellowish red (5YR 5/6) moist; moderate fine subangular blocky structure; slightly hard, friable, very sticky and very plastic; common fine roots; common very fine and fine interstitial and tubular pores; many distinct continuous calcium carbonate coatings on rock fragments; common fine and medium hard irregular calcium carbonate masses; 50 percent gravel; violently effervescent; moderately alkaline (pH 8.0); abrupt wavy boundary. (10 to 20 inches thick)
Bkm--32 to 40 inches; massive; indurated petrocalcic; violently effervescent. (6 to 20 inches thick)
R--40 inches; conglomerate.
TYPE LOCATION: Pima County, Arizona; latitude of 32 degrees 12 minutes and 30 seconds North and a longitude of 112 degrees 11 minutes and 30 seconds West. Near the center of sec. 17, T. 14 S., R. 2 E. Three miles west and north of Quijotoa trading post.
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.
Soil temperature: 69 to 72 degrees F.
Clay content: ranges from 20 to 50 percent; averages greater than 35 percent in the control section
Rock fragments: 40 to 75 percent gravel and/or cobble
Organic Matter: less than 0.5 percent
Depth to petrocalcic: 20 to 40 inches
Depth to bedrock: 25 to 60 inches
A horizon
Hue: 5YR, 7.5YR, 10YR
Value: 4 or 5 dry, 3 or 4 moist
Chroma: 4 through 6 dry, 2 through 4 moist
Calcium carbonate equivalent: 0 to 5 percent
Reaction: neutral to slightly alkaline
Bt horizon
Hue: 2.5YR, 5YR
Value: 4 or 5 dry, 3 or 4 moist
Chroma: 4 through 6, dry or moist
Texture: sandy clay, clay, sandy clay loam
Calcium carbonate equivalent: 5 to 15 percent
Reaction: slightly to moderately alkaline
Bk horizon
Hue: 5YR, 7.5YR
Value: 4 through 6 dry, 3 through 5 moist
Chroma: 4 through 6 dry, 5 or 6 moist
Calcium carbonate equivalent: 15 to 40 percent
Reaction: slightly to moderately alkaline
Bkm horizon
Cementation: Indurated or strongly cemented with calcium carbonate
COMPETING SERIES: This is the Nahda (AZ) series. Nahda soils do not have bedrock below the petrocalcic horizon.
GEOGRAPHIC SETTING: Caracara soils are on pediments and hills. Slopes range from 3 to 25 percent. These soils formed in fan alluvium from mixed sources but dominantly derived from conglomerate. Elevation ranges from 2000 to 3500 feet. The mean annual precipitation is 10 to 12 inches. The mean annual air temperature is 67 to 70 degrees F. The frost-free period is 240 to 260 days.
GEOGRAPHICALLY ASSOCIATED SOILS: These are the Delthorny, Vado, Arizo, and Stagecoach soils. Vado, Arizo, and Stagecoach soils are very deep. Delthorny soils do not have argillic horizons.
DRAINAGE AND PERMEABILITY: Well drained; medium runoff; slow permeability.
USE AND VEGETATION: Caracara soils are used for livestock grazing and wildlife habitat. Vegetation includes triangle bursage, paloverde, ocotillo, cacti, curly-mesquite, slender grama, bush muhly, threeawn, slender janusia, false mesquite and jojoba.
DISTRIBUTION AND EXTENT: Southern Arizona. This series is of moderate extent. MLRA is 40.
MLRA SOIL SURVEY REGIONAL OFFICE (MO) RESPONSIBLE: Phoenix, Arizona
SERIES ESTABLISHED: Pima County, Arizona; Soil survey of Tohono O'odham Indian Reservation, AZ, Parts of Maricopa, Pima and Pinal Counties; 1993.
REMARKS: Diagnostic horizons and features recognized in this pedon are:
Ochric epipedon - the zone from 0 to 1 inch (A horizon)
Argillic horizon - the zone from 1 to 19 inches (Bt, Btk horizons)
Calcic horizon - the zone from 19 to 32 inches (Bk horizon)
Petrocalcic horizon - the zone from 32 to 40 inches (Bkm horizon)
Lithic contact - the boundary at 40 inches (R horizon)
Classified according to Soil Taxonomy, Second Edition, 1999; Keys to Soil Taxonomy, Tenth Edition, 2006
Reviewed for the correlation of AZ661, 11/08, PDC