LOCATION ARIVACA AZEstablished Series
TAXONOMIC CLASS: Fine, smectitic, thermic Ustalfic Petrocalcids
TYPICAL PEDON: Arivaca very cobbly loam - rangeland. (Colors are for dry soil unless otherwise noted.)
A--0 to 1 inch; reddish brown (5YR 4/3) very cobbly loam, dark reddish brown (5YR 3/3) moist; moderate thin platy structure; slightly hard, very friable, slightly sticky and slightly plastic; common very fine roots; common very fine interstitial pores; 15 percent gravel and 20 percent cobble; neutral (pH 7.0); abrupt wavy boundary. (1 to 2 inches thick)
Bt1--1 to 4 inches; dark reddish gray (5YR 4/2) gravelly clay loam, dark reddish brown (5YR 3/2) moist; weak medium subangular blocky structure; hard, friable, sticky and plastic; common very fine roots; common fine tubular and interstitial pores; common faint clay films on faces of peds and lining pores; 15 percent gravel and 10 percent cobble; noneffervescent; slightly alkaline (pH 7.5); clear wavy boundary. (4 to 10 inches thick)
Bt2--4 to 8 inches; reddish brown (5YR 4/3) very gravelly clay loam, dark reddish brown (5YR 3/3) moist; weak medium subangular blocky structure; hard, firm, sticky and plastic; common very fine roots; common fine interstitial and tubular pores; common faint clay films on faces of peds and lining pores; 25 percent gravel and 15 percent cobble; noneffervescent; slightly alkaline (pH 7.5); abrupt wavy boundary. (4 to 10 inches thick)
Bt3--8 to 18 inches; reddish brown (5YR 4/4) clay, reddish brown (5YR 4/4) moist; strong medium prismatic structure; very hard, very firm, very sticky and very plastic; many very fine roots on ped faces; common very fine tubular pores; many prominent clay films on faces of peds and lining pores; many pressure faces; 5 percent gravel and 5 percent cobble; noneffervescent; moderately alkaline (pH 8.2); clear wavy boundary. (3 to 9 inches thick)
Btk--18 to 21 inches; reddish brown (5YR 5/4) and reddish brown (5YR 4/4) cobbly clay, dark reddish brown (5YR 3/4) moist; moderate fine subangular blocky structure; hard, friable, sticky and plastic; many very fine roots; common fine interstitial and few very fine tubular pores; common faint clay films on faces of peds and lining pores; few fine masses of calcium carbonate; strongly effervescent; moderately alkaline (pH 8.2); abrupt wavy boundary. (5 to 10 inches thick)
R--21 inches; porphyritic tuff, with a .5 inch thick calcium carbonate cemented hardpan with thin laminar cap.
TYPE LOCATION: Pima County, Arizona: Located about 2140 feet south and 715 feet east of the northwest corner of section 29, T.19 S., R.11 E.
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. The epipedon is moist in some part less than 90 days (cumulative) when the soil temperature is above 41 degrees F. in 7 out of 10 years. Ustic aridic soil moisture regime.
Soil temperature: 61 to 68 degrees F.
Depth to bedrock: 20 to 40 inches. The cemented hardpan is less than 1 inch thick and breaks down in acid.
Reaction: neutral to moderately alkaline
Organic matter: 0.3 to 1 percent in the surface
Rock fragments: 5 to 35 percent gravel and cobble in the particle-size control section
A horizon
Hue: 5YR, 7.5YR
Value: 3 through 5, dry or moist
Chroma: 2 or 3, dry or moist
Bt horizon
Hue: 5YR, 7.5YR
Value: 3 through 5, dry or moist
Chroma: 2 through 4, dry or moist
Texture: clay, clay loam
Btk horizon
Hue: 5YR, 7.5YR
Value: 4 through 7, dry or moist
Chroma: 4 through 6, dry or moist
Texture: clay, clay loam
Calcium carbonate equivalent: less than 15 percent
COMPETING SERIES: There are no competitors.
GEOGRAPHIC SETTING: Arivaca soils are on relict fan terraces. Slopes range from 2 to 15 percent. They formed in alluvium derived dominantly from basalt, conglomerate, and tuff. Elevation ranges from 3400 to 5500 feet. The mean annual precipitation is 12 to 16 inches. The mean annual air temperature is about 59 to 66 degrees F. The frost-free period is 180 to 240 days.
GEOGRAPHICALLY ASSOCIATED SOILS: These are the Whitehouse and Caralampi soils. These soils are very deep.
DRAINAGE AND PERMEABILITY: Well drained; medium runoff; slow permeability.
USE AND VEGETATION: Arivaca soils are used for livestock grazing and wildlife habitat. Vegetation includes tobosa, curly mesquite, sideoats grama, catclaw acacia, wolfberry and prickly pear cactus.
DISTRIBUTION AND EXTENT: Southern Arizona. This series is of small extent. MLRA is 41.
MLRA SOIL SURVEY REGIONAL OFFICE (MO) RESPONSIBLE: Phoenix, Arizona
SERIES ESTABLISHED: Pima County, Arizona; Soil survey of Pima County, Arizona, Eastern Part; 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 21 inches (Bt1, Bt2, Bt3, Btk horizons)
Petrocalcic horizon - The zone .5 inch thick directly underlain by bedrock (R horizon)
Lithic contact - The boundary at 21 inches (R horizon)
In October 2000, taxonomic classification was changed to recognize the presence of a petrocalcic horizon, described in the R horizon. Complete update should include a re-visit of the site and subsequent separate re-description of the petrocalcic horizon. Other placements may be more appropriate after a complete update.
Classified according to Keys to Soil Taxonomy Ninth Edition, 2003.