LOCATION OHACO              AZ
Established Series
Rev. PDC
04/2009

OHACO SERIES


The Ohaco series consists of moderately deep to a duripan, well drained soils formed in mixed alluvium. Ohaco soils are on stream terraces and fan terraces and have slopes of 0 to 5 percent. The average annual precipitation is about 10 inches and the mean annual temperature is about 68 degrees F.

TAXONOMIC CLASS: Fine, mixed, superactive, thermic Typic Argidurids

TYPICAL PEDON: Ohaco gravelly loam - rangeland. (Colors are for dry soil unless otherwise noted.)

A--0 to 2 inches; brown (7.5YR 5/4) gravelly loam, brown (7.5YR 4/4) moist; weak fine granular structure; slightly hard, very friable, nonsticky and nonplastic; common very fine roots; few very fine interstitial pores; 20 percent gravel and 5 percent cobble; noneffervescent; moderately alkaline (pH 8.0); clear smooth boundary. (1 to 3 inches thick)

Bt1--2 to 7 inches; yellowish red (5YR 5/6) clay loam; reddish brown (5YR 4/3) moist; moderate fine subangular structure; slightly hard, very friable, slightly sticky and plastic; common very fine roots; few very fine interstitial pores; few thin clay films on faces of peds; 5 percent gravel; noneffervescent; moderately alkaline (pH 8.0); clear smooth boundary. (1 to 5 inches thick)

Bt2--7 to 11 inches; yellowish red (5YR 4/6) clay loam, dark reddish brown (5YR 3/4) moist; moderate medium subangular blocky structure; slightly hard, friable, sticky and plastic; common very fine roots; common very fine tubular pores; few thin clay films lining pores and bridging mineral grains; 5 percent gravel; strongly effervescent; moderately alkaline (pH 8.0); clear wavy boundary. (4 to 6 inches thick)

Bt3--11 to 16 inches; yellowish red (5YR 4/6) clay loam, dark reddish brown (5YR 3/4) moist; strong coarse subangular blocky structure; hard, firm, sticky and plastic; common very fine roots; few very fine tubular pores; few thin clay films lining pores and bridging mineral grains; 5 percent gravel; strongly effervescent; moderately alkaline (pH 8.0); gradual wavy boundary. (5 to 8 inches thick)

Bt4--16 to 27 inches; yellowish red (5YR 4/6) clay, dark reddish brown (5YR 3/4) moist; strong coarse angular blocky structure; very hard, firm, very sticky and plastic; common very fine roots; common very fine tubular pores; common moderately thick clay films on faces of peds; 5 percent gravel; lime is disseminated and as thin filaments; strongly effervescent; moderately alkaline (pH 8.2); abrupt smooth boundary. (8 to 14 inches thick)

2C--27 to 31 inches; pink (5YR 8/3) gravelly sandy loam, light reddish brown (5YR 6/4) moist; massive; slightly hard, firm, slightly sticky and nonplastic; common very fine interstitial pores; 20 percent gravel; violently effervescent; moderately alkaline (pH 8.4); abrupt wavy boundary. (1 to 4 inches thick)

3Cqm--31 to 35 inches; indurated silica-lime cemented duripan with a thin laminar layer on the upper surface; extremely hard, violently effervescent. (4 to 24 inches thick)

TYPE LOCATION: Maricopa County, Arizona; 2,100 feet west and 500 feet north of the southeast corner of section 36, T. 7 N., R. 8 W. Latitude 33 degrees, 54 minutes, 2 seconds N., Longitude 113 degrees, 2 minutes, 39 seconds W., NAD 83

RANGE IN CHARACTERISTICS:

Soil moisture: Intermittently moist in some part of the SMCS during July-September and December-February. Typic aridic moisture regime.

Mean annual soil temperature: 67 to 72 degrees F.

Rock fragments: 10 to 50 percent rock fragments in the A horizon of which 10 to 30 percent are gravel. Averages less than 35 percent rock fragments in the control section.

Depth to duripan: 20 to 40 inches

Reaction: Usually moderately alkaline; is strongly alkaline in some pedons

A horizon
Hue: 7.5YR, 5YR
Value: 4 to 6 dry, 3 to 5 moist
Chroma: 3 to 6 dry, 3 or 4 moist
Texture: loam, clay loam (20 to 30 percent clay)
Carbonates: noneffervescent to strongly effervescent

Bt horizons
Hue: 7.5YR, 5YR
Value: 4 to 6 dry, 3 to 5 moist
Chroma: 3 to 6 dry, 3 or 4 moist
Texture: clay, clay loam (35 to 45 percent clay)
Carbonates: noneffervescent to violently effervescent

Bk horizon
Is present in some pedons above the duripan. Commonly present below the duripan.

C horizon
Absent in some pedons
Hue: 7.5Y, 5YR
Value: 6 to 8, dry, 5 or 6 moist
Chroma: 3 to 6, dry or moist

Texture: gravelly sandy loam

COMPETING SERIES: This is the Frye (AZ) series. Frye soils have mean annual soil temperatures less than 67 degrees F.

GEOGRAPHIC SETTING: Ohaco soils are on stream terraces and fan terraces and have slopes of 0 to 5 percent. They formed in mixed alluvium from acid and basic igneous rocks. Elevation is 1,800 to 2,500 feet. The climate is warm arid continental. Average annual precipitation is 8 to 12 inches occurring as summer thunderstorms and gentle winter rain. Mean annual air temperature is 64 to 70 degrees F. The frost-free period is about 220 to 270 days.

GEOGRAPHICALLY ASSOCIATED SOILS: These are the Continental, Dona Ana, Guest, Mohave, Pinaleno and Tres Hermanos soils. All of these soils are very deep.

DRAINAGE AND PERMEABILITY: Well drained; slow runoff; slow permeability.

USE AND VEGETATION: Used for livestock grazing. The native vegetation is mesquite, creosotebush, prickly pear, cholla, Indianwheat, saguaro, tobosa, triangle bursage and annual grasses.

DISTRIBUTION AND EXTENT: South Central Arizona. The series is not extensive. Total extent is about 4,100 acres. MLRA is 40.

MLRA SOIL SURVEY REGIONAL OFFICE (MO) RESPONSIBLE: Phoenix, Arizona

SERIES ESTABLISHED: Maricopa County, Arizona, 1982.

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 27 inches (Bt horizons)

Duripan- the zone from 31 to 35 inches (3Cqm horizons)

Classified according to Soil Taxonomy, Second Edition, 1999; Keys to Soil Taxonomy Tenth Edition, 2006.

Revised for the correlation of AZ661, 2/2009, WWJ


National Cooperative Soil Survey
U.S.A.