LOCATION RILLITO AZEstablished Series
TAXONOMIC CLASS: Coarse-loamy, mixed, superactive, hyperthermic Typic Haplocalcids
TYPICAL PEDON: Rillito gravelly sandy loam - rangeland. (Colors are for dry soil unless otherwise noted.)
A--0 to 1 inch; light yellowish brown (10YR 6/4) gravelly sandy loam, brown (10YR 4/3) moist; weak medium platy structure; slightly hard, very friable, nonsticky and nonplastic; many fine roots; common very fine tubular pores; strongly effervescent; moderately alkaline (pH 8.0); abrupt smooth boundary. (1/2 to 2 inches thick)
Bw--1 to 5 inches; light brown (7.5YR 6/4) gravelly sandy loam, brown (7.5YR 4/4) moist; weak fine granular structure; slightly hard, friable, nonsticky and nonplastic; common fine roots; common very fine pores; strongly effervescent and pockets that are violently effervescent; moderately alkaline (pH 8.2); abrupt smooth boundary. (3 to 8 inches thick)
Bk1--5 to 12 inches; pink (7.5YR 8/4) gravelly loam, light brown (7.5YR 6/4) moist; massive; hard, friable, slightly sticky and slightly plastic; few fine roots; few very fine tubular pores; many fine soft calcium carbonate masses; violently effervescent; moderately alkaline (pH 8.4); clear smooth boundary. (5 to 14 inches thick)
Bk2--12 to 24 inches; very pale brown (10YR 8/2) weakly lime-cemented gravelly sandy loam, very pale brown (10YR 7/3) moist; massive; very hard, very firm, slightly sticky and slightly plastic; few very fine tubular pores; many medium calcium carbonate masses; violently effervescent; moderately alkaline (pH 8.4); gradual wavy boundary. (10 to 30 inches thick)
C--24 to 60 inches; pinkish gray (7.5YR 7/2) sandy loam, brown (10YR 5/3) moist; massive; soft, very friable, nonsticky and nonplastic; many very fine irregular pores; 10 percent gravel; strongly effervescent; moderately alkaline (pH 8.4).
TYPE LOCATION: Maricopa County, Arizona; 1400 feet west and 1050 feet north of the southeast corner of section 16, T. 2 N., R. 1 W.
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 - 72 to 77 degrees F.
Depth to calcic horizon - 3 to 40 inches
Sodium adsorption ratio - Ranges to 40 in some pedons
Calcium carbonate - Effervescent throughout, calcium carbonate accumulations occur as soft masses or as a continuous weakly cemented horizon.
Electrical conductivity - Less than 8, but ranges to 16 in some pedons
Rock fragments - 5 to 60 percent gravel in any single horizon, but the control section average is 15 to 35 percent. The surface layer contains 5 to 35 percent gravel. In some pedons, the rock fragments are dominantly calcium carbonate concretions and durinodes.
Texture- Fine sandy loam, sandy loam, loam (10 to 25 percent clay), some pedons have thin layers of finer or coarser textures.
Reaction - Moderately to very strongly alkaline
A horizon
Hue: 5YR, 7.5YR, 10YR
Value: 4, 5, 6 or 7 dry, 4, 5 or 6 moist
Chroma: 2, 3, 4, or 6 dry, 2, 3, 4, 6 or 7 moist
Bw and Bk horizons
Hue: 7.5YR, 10YR
Value: 5, 6, 7 or 8 dry, 4, 5, 6, 7 or 8 moist
Chroma: 1, 2, 3 or 4, dry or moist
Cementation: Weakly calcium carbonate - cemented or noncemented
C horizon
Hue: 7.5YR, 10YR
Value: 6, 7 or 8 dry, 4, 5, 6, 7 or 8 moist
Chroma: 2, 3 or 4 dry, 2 or 3 moist
COMPETING SERIES: These are the Aco (CA), Coolidge (AZ), Garywash (CA), Laveen (AZ), and Toltec (AZ) series. Aco soils are in the Colorado Desert portion of southeast California (MLRA 31) receive mostly winter precipitation and are usually dry April through November. Coolidge and Laveen soils have less than 15 percent coarse fragments in the control section. Also, Laveen soils are medium textured. Garywash soils are in the Colorado Desert portion of southeast California (MLRA 31) receive mostly winter precipitation and are usually dry April through November and have secondary accumulations of silica and gypsum in the control section. Toltec soils have a calcic horizon that consists of a disintegrated hardpan.
GEOGRAPHIC SETTING: Rillito soils are on fan terraces or stream terraces and have slopes of 0 to 40 percent. These soils formed in alluvium from mixed sources. Elevations range from 400 to 2200 feet. Rillito soils are in a hot, arid and continental climate. The mean annual air temperature ranges from 67 to 75 degrees F. The mean annual precipitation ranges from 3 to 10 inches. Precipitation falls as summer thunderstorms and gentle winter rains. The frost-free period is about 240 to 350 days.
GEOGRAPHICALLY ASSOCIATED SOILS: These are the competing Coolidge and Laveen soils, and the Antho, Mohall, Pinamt, Tremant and Valencia soils. Antho soils do not have a calcic horizon and have less than 15 percent coarse fragments. Mohall, Pinamt, Tremant and Valencia soils have argillic horizons.
DRAINAGE AND PERMEABILITY: Somewhat excessively drained; slow or medium runoff; moderate permeability.
USE AND VEGETATION: Irrigated areas are used to produce crops such as cotton, alfalfa, small grains and citrus. The desert areas are used to a limited extent for livestock grazing. The vegetation is mainly creosotebush, desert sage, cacti, mesquite, paloverde, ironwood, and annual grasses and weeds.
DISTRIBUTION AND EXTENT: Southern Arizona. Rillito soils are moderately extensive. MLRA is 40.
MLRA SOIL SURVEY REGIONAL OFFICE (MO) RESPONSIBLE: Phoenix, Arizona
SERIES ESTABLISHED: Pima County, Arizona; 1945.
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 5 to 24 inches (Bk1, Bk2 horizons)
Classified according to Soil Taxonomy Second Edition, 1999