LOCATION SIGNAL AZEstablished Series
TAXONOMIC CLASS: Clayey-skeletal, smectitic, thermic Aridic Paleustolls
TYPICAL PEDON: Signal very gravelly loam - rangeland. (Colors are for dry soil unless otherwise specified.)
A--0 to 2 inches; dark grayish brown (10YR 4/2) very gravelly loam, dark brown (7.5YR 3/2) moist; weak medium platy structure; slightly hard, friable, sticky and slightly plastic; many very fine and few common roots; many very fine interstitial and few very fine tubular pores; 40 percent fine and medium pebbles; moderately acid (pH 6.0); abrupt wavy boundary. (1 to 4 inches thick)
Bt1--2 to 7 inches, dark brown (7.5YR 3/2) very gravelly clay loam, dark reddish brown (5YR 2/2) moist; weak very fine subangular blocky structure; slightly hard, friable, sticky and plastic; many very fine roots; many very fine interstitial and tubular pores; common moderately thick clay films on faces of peds; 40 percent pebbles and 10 percent cobbles; neutral (pH 7.0); abrupt wavy boundary. (3 to 6 inches thick)
Bt2--7 to 13 inches; reddish brown (5YR 4/3) very gravelly clay, dark reddish brown (5YR 3/3) moist; moderately fine and very fine subangular blocky structure; very hard, friable, sticky and very plastic; many very fine roots; many very fine interstitial and few very fine tubular pores; 45 percent pebbles and 5 percent cobbles; common moderately thick clay films on faces of peds; slightly alkaline (pH 7.5); clear wavy boundary. (5 to 10 inches thick)
Bt3--13 to 22 inches; reddish brown (5YR 4/4) crushed, very gravelly clay, reddish brown (5YR 4/4) crushed, moist; moderate medium prismatic structure parting to moderate medium subangular blocky; very hard, friable, sticky and plastic; common very fine roots; many very fine interstitial pores; 40 percent pebbles; common moderately thick clay films on faces of peds; slightly alkaline (pH 7.5); abrupt wavy boundary. (6 to 10 inches thick)
Btk--22 to 32 inches; reddish brown (5YR 5/4) very gravelly sandy clay, reddish brown (5YR 4/4) moist; weak fine subangular blocky structure; very hard, friable, sticky and plastic; few very fine roots; many very fine interstitial pores; common thin clay films on faces of peds; 60 percent fine pebbles; slightly effervescent; few fine white (5YR 8/1) soft lime masses; moderately alkaline (pH 8.0); abrupt wavy boundary. (0 to 10 inches thick)
2Ck--32 to 42 inches; brown (7.5YR 5/4) and pink (7.5YR 7/4) very gravelly sandy loam, brown (7.5YR 5/4) moist; massive; very hard, friable, nonsticky and nonplastic; few very fine tubular pores; 50 percent fine pebbles; strongly effervescent; moderately alkaline (pH 8.0); abrupt wavy boundary. (6 to 15 inches thick)
2C--42 to 60 inches; strong brown (7.5YR 5/6) very gravelly loamy sand, brown (7.5YR 4/4) moist; massive; hard, friable; few very fine tubular pores; 50 percent fine pebbles; moderately alkaline (pH 8.0).
TYPE LOCATION: Graham County, Arizona; approximately 6 miles north of the junction of I-10 and U.S. Highway 666; thence 2-1/2 miles west of U.S. Highway 666 to section 33; 800 feet east and 2,600 feet north of the SW corner of sec. 33, T. 11 S., R. 26 E.
RANGE IN CHARACTERISTICS:
Solum thickness: 15 to 40 inches
Mollic epipedon thickness: 12 or more inches
Soil moisture: The moisture control section is dry more than six-tenths of the time most years when the soil temperature is more than 15 degrees C. Aridic ustic moisture regime.
Coarse fragments: average more than 35 percent in the 10- to 40-inch section.
A horizon
Color: very dark grayish brown, dark grayish brown, dark brown or brown
Texture: gravelly loam, very gravelly loam or cobbly loam
Organic matter content: more than 1 percent.
B2t horizon
Color: dark brown, dark reddish brown, brown or reddish brown
Hue: 7.5YR or 5YR
Value: 3 or 4 dry and 2 or 3 moist
Texture: clay loam or clay
Coarse fragments: averages more than 35 percent
C horizon
Texture: clay, sandy clay loam, sandy loam or loamy sand
Coarse fragments: averages more than 50 percent
Calcium carbonate: a zone of calcium carbonate accumulation that is weakly cemented occurs in some pedons.
COMPETING SERIES: There are no competing series.
GEOGRAPHIC SETTING: Signal soils are on fans of old valley filling materials. Slopes are 1 to 30 percent, dominantly 4 to 15 percent. Elevations are 3,400 to 5,000 feet. The climate is semiarid and warm. Summers are hot and winters are cool. The average January temperature is 48 degrees F. The average July temperature is 80 degrees F., and the mean annual temperature is 57 degrees to 69 degrees F. The frost-free season is 180 to 260 days. The average annual precipitation ranges from 12 to 16 inches and occurs mainly as thunderstorms in July and August and as gentle rains in December and January.
GEOGRAPHICALLY ASSOCIATED SOILS: These are the Arizo, Atascosa, Graham, Sonoita and Tubac soils and the competing Continental and White House soils. Arizo soils lack mollic epipedons and argillic horizons. Atascosa and Graham soils have a lithic contact. Sonoita and Tubac soils lack a mollic epipedon and have less than 35 percent coarse fragments.
DRAINAGE AND PERMEABILITY: Well drained; medium runoff; slow permeability.
USE AND VEGETATION: Used only for range. Present vegetation is desert shrub and grasses. Grasses are tobosa, bush muhly, sideoats and black grama, and threeawn. Shrubs are mesquite and catclaw.
DISTRIBUTION AND EXTENT: Southeastern Arizona. The soils are moderately extensive. MLRA 41 & 42.
MLRA SOIL SURVEY REGIONAL OFFICE (MO) RESPONSIBLE: Phoenix, Arizona
SERIES ESTABLISHED: Upper Gila River Project, Arizona, 1937.
REMARKS: This revision of the Signal series changes the classification and type location. The previous type location was in the soil survey of Santa Cruz and parts of Cochise and Pima Counties, Arizona. At that location the soils were marginal between fine and clayey-skeletal. Additional field observations indicated that the soils would be dominantly clayey-skeletal. The new type location better represents a clayey-skeletal family and the area of distribution.