LOCATION ORRUBO                  AZ+NV

Established Series
BAL/RKS/DWD/HCD/ET
12/2015

ORRUBO SERIES

The Orrubo series consists of very shallow and shallow to a petrocalcic, well drained soils formed in colluvium and residuum from calcareous fanglomerate. Orrubo soils are on summits and side slopes of ballenas, fan remnants and fan terraces. Slopes range from 2 to 35 percent. The mean annual precipitation is about 7 inches and the mean annual air temperature is about 65 degrees F.

TAXONOMIC CLASS: Loamy-skeletal, carbonatic, thermic, shallow Calcic Petrocalcids

TYPICAL PEDON: Orrubo very gravelly sandy loam recreation, and wildlife habitat. (Colors are for dry soil unless otherwise noted.) The soil surface is partially covered with 45 percent gravel composed of pan fragments, limestone and calcareous sandstone.

A--0 to 2 inches; brown (7.5YR 5/4) very gravelly loam, brown (7.5YR 4/4) moist; weak fine and medium subangular blocky structure; soft, very friable, nonsticky and nonplastic; many very fine roots; common very fine and few fine tubular pores; 45 percent calcium carbonate equivalent; violently effervescent; 50 percent gravel; moderately alkaline (pH 8.2); abrupt smooth boundary. (1 to 2 inches thick.)

Bk1--2 to 7 inches; light brown (7.5YR 6/4) very gravelly fine sandy loam, strong brown (7.5YR 4/6) moist; moderate medium and coarse subangular blocky structure; slightly hard, very friable, nonsticky and nonplastic; common very fine and few fine roots; common very fine and few fine tubular pores; many thick coats and pendants of calcium carbonate on underside of coarse fragments; 35 percent calcium carbonate equivalent; violently effervescent; 40 percent gravel; moderately alkaline (pH 8.2); clear smooth boundary.

Bk2--7 to 13 inches; pink (7.5YR 7/3) extremely gravelly loam, brown (7.5YR 5/4) moist; massive; soft, very friable, slightly sticky and moderately plastic; few fine roots; few very fine tubular pores; many thick coats and pendants of calcium carbonate on coarse fragments; 55 percent calcium carbonate equivalent; violently effervescent; 70 percent gravel; moderately alkaline (pH 8.4); abrupt irregular boundary. (The combined thickness of the Bk horizons is 6 to 18 inches.)

Bkm--13 to 19 inches; white (10YR 8/1) continuously indurated petrocalcic, pink (7.5YR 7/3) moist; abrupt wavy boundary.

Cr--19 to 60 inches; fanglomerate.

TYPE LOCATION: Mohave County, Arizona, near Grand Wash on Lake Mead National Recreation Area; 1,500 feet south and 1,800 feet east of the northwest corner of section 12, T. 33 N., R. 16 W.; 36 degrees, 17 minutes, 15 seconds north latitude and 113 degrees, 57 minutes, 25 seconds west longitude.

RANGE IN CHARACTERISTICS:

Soil moisture: Intermittently moist in some part of the soil moisture control section during December - February and for less than 20 days cumulative during July - September. Driest during May and June. Typic aridic soil moisture regime.

Soil temperature: 59 to 72 degrees F.

Rock fragments: 35 to 75 percent

Depth to hardpan: 8 to 20 inches

Depth to paralithic contact: 17 to 30 inches

Organic matter content: Less than 1 percent

Reaction: Slightly alkaline or moderately alkaline

Calcium carbonate equivalent: Averages 40 to 60 percent by weight in the less than 20 millimeter fraction.

Clay content: Average 5 to 18 percent in the particle-size control section

A horizon - Hue: 7.5YR, 10YR
Value: 5 or 6 dry, 4 through 6 moist
Chroma: 2 through 4, dry or moist

Bk horizon - Hue: 7.5YR, 10YR
Value: 6 through 8 dry, 4 through 8 moist
Chroma: 3 through 6, dry or moist

Bkm horizon - Hue: 7.5YR or 10YR
Value: 7 or 8 dry, 6 or 7 moist
Chroma: 1 through 4, dry or moist

Cr horizon - Other features: Consists of fanglomerate that is dominated by gravel and cobble-sized limestone, calcareous sandstone or other calcareous clasts. It is rigid through very rigid when dry, friable through extremely firm when moist. Noncemented through strongly cemented. Approximately 10 to 25 percent of an air dried sample slakes when submerged in water.

COMPETING SERIES: These are the Ferrogold (NV), Infantry (NM), Neso (NM), Philder (NM), Sutherland (AZ), Paisano (TX) Tencee (NM), Wechech (T)(NV)and Wodavar (NV)series. All of these soils are more than 60 inches deep to a paralithic contact. In addition, Infantry, Neso, Paisano, Philder, Tencee and Sutherland soils have a greater summer rainfall component typical of MLRA 41 and MLRA 42.

GEOGRAPHIC SETTING: Orrubo soils are on summits and side slopes of fan terraces, fan remnants and ballenas at elevations of 1,400 to 2,300 feet. These soils formed in colluvium and residuum derived from calcareous fanglomerate. Slopes range from 2 to 35 percent. The mean annual precipitation is 5 to 9 inches and occurs as thunderstorms during July to September and as gentle rains during December and January. The mean annual air temperature is 57 to 70 degrees F. The frost-free period is 210 to 280 days.

GEOGRAPHICALLY ASSOCIATED SOILS: These are the Arizo and Meadview soils. Arizo and Meadview soils are very deep.

DRAINAGE AND PERMEABILITY: Well drained; low to very high runoff; moderately rapid permeability.

USE AND VEGETATION: Orrubo soils are used for livestock grazing, wildlife habitat. Vegetation includes creosotebush, white bursage, red brome, globemallow, sixweeks fescue, hedgehog cactus, white ratany, cholla, desert trumpet and Indian wheat.

DISTRIBUTION AND EXTENT: Mojave Desert of northwestern Arizona and southern Nevada; MLRA 30. Orrubo series are not extensive.

MLRA SOIL SURVEY REGIONAL OFFICE (MO) RESPONSIBLE: PHOENIX, ARIZONA

SERIES ESTABLISHED: Mohave County, Arizona; Soil survey of Grand Canyon Area, Arizona, 2001.

REMARKS: Diagnostic horizons and features recognized in this pedon are:

Ochric epipedon - 0 to 2 inches (A horizon).

Calcic horizon - 2 to 13 inches (Bk1 and Bk2 horizons).

Petrocalcic horizon - 13 to 19 inches (Bkm horizon).

Paralithic contact - 19 inches (Cr layer).

Particle-size control section 0 to 13 inches (A, Bk1 and Bk2 horizons).

Series originally proposed in Mohave County, Arizona, soil survey of Lake Mead National Recreation Area, 1997.

Classified according to Keys to Soil Taxonomy Ninth Edition, 2003.

Responsibility for this series was transferred from Davis to Phoenix 12/2015. The last revision to the series was 12/2006. ET

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National Cooperative Soil Survey
U.S.A.