LOCATION LITTLEGRASS ORTentative Series
TAXONOMIC CLASS: Fine-loamy, mixed, superactive, frigid Vitritorrandic Argixerolls
TYPICAL PEDON: Littlegrass ashy silt loam at an elevation of 1,480 meters, rangeland. (Colors are for dry soil unless otherwise noted.) The surface is partly covered by 1 percent gravel.
A--0 to 14 cm; brown (10YR 5/3) ashy silt loam, dark brown (10YR 3/3) moist; weak medium granular structure; soft, very friable, slightly sticky, slightly plastic; many fine and very fine roots; common interstitial and tubular pores; 2 percent fine gravel and 2 percent gravel; slightly alkaline (pH 7.4); clear smooth boundary. (8 to 25 cm thick)
AB--14 to 28 cm; grayish brown (10YR 5/2) ashy silt loam, dark brown (10YR 3/3) moist; weak medium and fine subangular blocky structure; hard, very firm, slightly sticky, slightly plastic; many fine, common medium and very fine roots; many fine interstitial and common medium interstitial and tubular pores; 2 percent fine gravel and 2 percent gravel; slightly alkaline (pH 7.4); clear smooth boundary. (9 to 32 cm thick)
Bt1--28 to 62 cm; brown (10YR 4/3) ashy silt loam, dark yellowish brown (10YR 3/4) moist; moderate medium and fine subangular blocky structure; hard, very firm, slightly sticky, slightly plastic; common very fine, fine, and medium roots; many fine and common very fine interstitial pores, common fine and medium tubular pores; 20 percent distinct clay films on all faces of peds; 2 percent fine gravel and 2 percent gravel; slightly alkaline (pH 7.4); clear smooth boundary. (16 to 47 cm thick)
Bt2--62 to 87 cm; brown (10YR 4/3) ashy silt loam, dark yellowish brown (10YR 3/4) moist; moderate fine and medium subangular blocky structure; hard, very firm, slightly sticky, slightly plastic; common fine and very fine roots; many fine and very fine interstitial pores; 30 percent distinct clay films on all faces of peds; 2 percent fine gravel and 2 percent gravel; slightly alkaline (pH 7.4); clear smooth boundary. (13 to 49 cm thick)
Bt3--87 to 112 cm; yellowish brown (10YR 5/4) ashy silty clay loam, brown (10YR 4/3) moist; weak fine and medium subangular blocky structure; hard, very firm, slightly sticky, slightly plastic; common very fine and fine roots; many very fine and fine interstitial pores; 5 percent distinct clay films on all faces of peds and 30 percent distinct pressure faces; 2 percent fine gravel, 2 percent gravel, and 2 percent cobbles; slightly alkaline (pH 7.4); clear smooth boundary. (16 to 25 cm thick)
Cr--112 to 116 cm; moderately cemented tuff; slightly alkaline (pH 7.4); abrupt smooth boundary. (2 to 10 cm thick)
R--116 cm; indurated tuff.
TYPE LOCATION: Malheur County, Oregon; approximately 10 miles southwest of Jordan Valley, Oregon; UTM 485184 easting and 4740483 northing, zone 11, NAD83 on the USGS Juniper Ridge 7.5 minute quadrangle, latitude 42 degrees 49 minutes 0.3 seconds north and longitude 117 degrees 10 minutes 52.5 seconds west, NAD83.
RANGE IN CHARACTERISTICS:
Soil moisture: The soil moisture control section is dry throughout in late summer and fall and moist in winter, spring, and early summer; Aridic moisture regime that borders on xeric.
Soil temperature: The mean annual soil temperature is 7 to 8 degrees C.
Mollic epipedon thickness - 28 to 50 cm, includes the upper part of the Bt in some pedons.
Depth to paralithic contact - 102 to 112 cm.
Depth to hard bedrock - 105 to 117 cm.
Control section - Clay content - 20 to 35 percent.
Rock fragments - 5 to 35 percent, mainly gravel of tuff lithology.
A horizon -
Value: 4 to 6 dry.
Volcanic glass: Volcanic glass is estimated to range from 30 to 50 percent of the 0.02 to 2 mm fraction
AB horizon -
Value: 3 to 5 dry.
Texture: Ashy silt loam, loam.
Clay content: 18 to 25 percent.
Rock fragments: Averages 5 to 30 percent, mainly gravel.
Volcanic glass: Volcanic glass is estimated to range from 5 to 30 percent of the 0.02 to 2 mm fraction
Bt horizons -
Value: 4 or 5 dry, 3 or 4 moist.
Texture: Ashy silty clay loam, ashy clay loam, ashy silt loam.
Clay content: 20 to 35 percent.
Rock fragments: Averages 5 to 35 percent, mainly gravel.
Volcanic glass: Volcanic glass is estimated to range from 5 to 30 percent of the 0.02 to 2 mm fraction
COMPETING SERIES: These are the Dester soils. Dester soils are 50 to 100 cm to hard bedrock.
GEOGRAPHIC SETTING: Littlegrass soils are on lava plateaus. These soils formed in mixed loess and volcanic ash over residuum weathered from tuff and basalt. Slope ranges from 2 to 15 percent. Elevations are 1,370 to 1,495 meters. The climate is semiarid with cold, moist winters and warm, dry summers. The mean annual precipitation is 280 to 330 mm; mean annual temperature is 5 to 7 degrees C, and the frost-free period is 50 to 80 days.
GEOGRAPHICALLY ASSOCIATED SOILS: These are the Drice soils. Drice soils are 50 to 100 cm to bedrock and are moderately well drained.
DRAINAGE AND SATURATED HYDRAULIC CONDUCTIVITY: Well drained, high runoff, very slow and slow permeability, and moderately low saturated hydraulic conductivity.
USE AND VEGETATION: Rangeland and wildlife habitat. The present vegetation is mainly basin big sagebrush, bluebunch wheatgrass, and Idaho fescue.
DISTRIBUTION AND EXTENT: Southeast Oregon; the soil is of moderate extent. MLRA 25.
MLRA SOIL SURVEY REGIONAL OFFICE (MO) RESPONSIBLE: Davis, California.
SERIES PROPOSED: Malheur County, Oregon, Southern Part, 2008.
REMARKS: Diagnostic horizons and features recognized in this pedon are:
Mollic Epipedon - The zone from the soil surface to about 28 cm (A and AB horizons).
Argillic horizon - The zone from about 24 to 112 cm. (Bt1, Bt2, and Bt3 horizons)
Vitritorrandic feature - Aridic moisture regime bordering on xeric. Volcanic glass is 30 to 50 percent of the 0.02 to 2 mm fraction in the zone from 0 to 24 cm (A horizons). Volcanic glass is 5 to 30 percent of the 0.02 to 2 mm fraction in the zone from 14 to 112 cm (AB and all Bt horizons)
Particle-size control section - The zone from 28 to 78 cm (Bt1, Bt2 and part of the Bt3 horizons).