LOCATION ALIBI IDEstablished Series
TAXONOMIC CLASS: Fine, smectitic, mesic Typic Palexerolls
TYPICAL PEDON: Alibi very stony loam -- on a northwest-facing slope of 18 percent, in native rangeland, at 4,500 feet elevation. The surface is covered by 3 percent stones. (Colors are for air-dry soil unless otherwise stated.)
A--0 to 4 inches; brown (10YR 5/3) very stony loam, dark brown (10YR 3/3) moist; moderate fine granular structure; soft, very friable, slightly sticky and plastic; common very fine and fine roots; many very fine and fine interstitial pores; 35 percent gravel, 5 percent cobbles, 5 percent stones; slightly acid (pH 6.4); clear smooth boundary. (2 to 7 inches thick)
AB--4 to 7 inches; brown (10YR 5/3) gravelly loam, dark brown (10YR 3/3) moist; moderate fine and medium subangular blocky structure parting to strong fine and medium granular; slightly hard, friable, very sticky and plastic; common very fine and fine roots; many very fine tubular pores; common thin clay films on faces of peds; 15 percent gravel, 2 percent cobbles; slightly acid (pH 6.4); abrupt smooth boundary. (0 to 6 inches thick)
Bt1--7 to 12 inches; yellowish brown (10YR 5/4) gravelly clay, brown (10YR 4/3) moist; moderate medium prismatic structure parting to strong fine and medium angular blocky; very hard, very firm, very sticky and very plastic; few very fine and fine roots; common very fine tubular pores; common pressure faces; many thick clay films on faces of peds and in pores; 15 percent gravel, 2 percent cobbles; neutral (pH 6.6); clear smooth boundary. (5 to 8 inches thick)
Bt2--12 to 17 inches; brown (7.5YR 5/4) gravelly clay, dark brown (7.5YR 4/4) moist; strong fine and medium angular blocky structure; hard, firm, sticky and very plastic; few very fine and fine roots; common very fine tubular pores; many thick films on faces of peds; 20 percent gravel, 5 percent cobbles; mildly alkaline (pH 7.4); clear smooth boundary. (4 to 7 inches thick)
Bq--17 to 23 inches; pink (7.5YR 7/4) very gravelly sandy loam, brown (7.5YR 5/4) moist; massive; slightly hard, very friable; few very fine and fine roots; common very fine and fine interstitial and tubular pores; 45 percent gravel, 10 percent cobbles; most rock fragments are coated with secondary silica; mildly alkaline (pH 7.6); gradual smooth boundary. (3 to 10 inches thick)
R--23 + inches; fractured moderately weathered rhyolite.
TYPE LOCATION: Owyhee County, Idaho; approximately 11 1/2 miles southwest of Oreana; 2,300 feet west and 1,800 feet south of the northeast corner of section 1, T.6S., R.2W.
RANGE IN CHARACTERISTICS:
Mollic epipedon thickness and depth to abrupt textural change - 7 to 10 inches
Depth to base of argillic - 17 to 23 inches
Depth to bedrock - 20 to 30 inches
Average annual soil temperature - 48 to 52 degrees
Other features - the surface is covered with 30 to 70 percent rock fragments
A and AB horizons
Value - 4 or 5 dry, 2 or 3 moist
Chroma - 2 or 3 dry or moist
Rock fragments - 20 to 50 percent
Reaction (pH) - slightly acid to neutral
Bt horizons
Hue - 10YR or 7.5YR
Value - 5 or 6 dry, 4 or 5 moist
Chroma - 3 or 4 dry or moist
Texture - GR-C, C, or GR-CL
Percent clay - 35 to 50
Rock fragments - 10 to 35 percent (mostly gravel)
Reaction (pH) - neutral to mildly alkaline
Bq horizon
Value - 6 or 7 dry, 4 or 5 moist
Chroma - 3 or 4 dry or moist
Texture - GRV-SL, GRV-SCL, or CBV-SCL
Rock fragment content - 35 to 60 percent
Reaction (pH) - neutral to mildly alkaline
COMPETING SERIES: These are the Coleman, Dry Creek, Lasere, Pomponio, Pritchard, Succor, and Tutuilla series. Coleman, Dry Creek, and Pritchard soils are greater than 60 inches to bedrock. Lasere soils have less than 10 percent rock fragment in the Bt horizon and lack layers of silica accumulation. Pomponio soils are moderately deep to a paralithic contact and have chromas of 1 or 2 throughout. Succor soils are very deep. Tutuilla soils have a paralithic contact between 40 and 60 inches.
GEOGRAPHIC SETTING: Alibi soils are undulating to steep on sideslopes of foothills. These soils formed in slope alluvium and residuum from rhyolite and welded rhyolitic tuff. Slopes range from 3 to 35 percent. Elevations are 3,700 to 5,250 feet. The climate is characterized by hot, dry summers and cool, moist winters. The average annual precipitation ranges from 12 to 15 inches and the average annual air temperature ranges from 45 to 50 degrees F. The frost-free period is 90 to 125 days.
GEOGRAPHICALLY ASSOCIATED SOILS: These are the Chinabutte soils. Chinabutte soils are shallow over bedrock and occur on sideslopes and shoulders of foothills, usually above Alibi soils on the landscape.
DRAINAGE AND PERMEABILITY: Well drained; medium to rapid runoff; slow permeability.
USE AND VEGETATION: Alibi soils are used for rangeland and wildlife habitat. The dominant natural vegetation is low sagebrush, Idaho fescue, and bluebunch wheatgrass.
DISTRIBUTION AND EXTENT: Southwestern Idaho. Alibi soils are of small extent.
MLRA OFFICE RESPONSIBLE: Reno, Nevada
SERIES ESTABLISHED: Owyhee County Area, Idaho, 1992.
REMARKS: Diagnostic horizons and features recognized in this pedon:
Mollic epipedon greater than 1/3 the depth to the base of the argillic - zone 0 to 7 inches (A and AB horizons)
Argillic horizon and particle-size control section - zone 7 to 17 inches (Bt1 and Bt2 horizons)
"Siliceous" horizon - zone 17 to 23 inches (Bq horizon)