LOCATION EVNA COTentative Series
TAXONOMIC CLASS: Clayey-skeletal, smectitic Ustic Argicryolls
TYPICAL PEDON: Evna stony loam, on a southwest facing, 40 percent slope in rangeland at an elevation of 7520 feet. (Colors are for dry soil unless otherwise noted.) When described on October 6, 1992 the soil was dry throughout. The surface is covered by 2 percent stones.
A--0 to 11 inches; dark grayish brown (10YR 4/2) stony loam, very dark grayish brown (10YR 3/2) moist; moderate fine subangular blocky structure parting to moderate medium granular; slightly hard, friable, moderately sticky and moderately plastic; many coarse, fine, very fine, and common medium roots; 5 percent gravel, 10 percent cobbles, 15 percent stones; neutral (pH 6.9); gradual wavy boundary. (10 to 15 inches thick)
Bt1--11 to 22 inches; dark grayish brown (10YR 4/2) very stony clay loam, brown (10YR 4/3) moist; strong medium subangular blocky structure parting to strong fine subangular blocky; hard, firm, moderately sticky and moderately plastic; many coarse and medium, common fine and very fine roots; few fine tubular pores; many continuous distinct clay films on faces of peds; 10 percent gravel, 20 percent cobbles, 20 percent stones; neutral (pH 7.2); gradual wavy boundary.
Bt2--22 to 48 inches; dark grayish brown (10YR 4/2) extremely stony clay, dark grayish brown (10YR 4/2) moist; moderate very coarse prismatic structure; very hard, very firm, very sticky and very plastic; common coarse, medium, and fine roots; few fine tubular pores; many continuous prominent clay films on faces of peds; 10 percent gravel, 25 percent cobbles, 30 percent stones; neutral (pH 7.2); gradual wavy boundary.
Bt3--48 to 65 inches; yellowish brown (10YR 5/4) very stony clay, brown (10YR 4/3) moist; weak coarse prismatic structure; very hard, very firm, very sticky and very plastic; common coarse, medium and fine roots; few fine tubular pores; many continuous prominent clay films on faces of peds; 5 percent gravel, 15 percent cobbles, 15 percent stones; neutral (pH 7.2). (The combined thickness of the Bt horizon is 55 to 80 inches thick)
TYPE LOCATION: Routt County, Colorado; about 11 miles northeast of Hayden, Colorado; located about 2,300 feet south and 1,750 feet west of the northeast corner of sec. 20, T. 8 N., R. 87 W.; Quaker Mountain USGS quad; lat. 40 degrees 38 minutes 13 seconds N. and long. 107 degrees 10 minutes 8 seconds W., NAD 27
RANGE IN CHARACTERISTICS:
Soil moisture:
Soil moisture regime subclass: ustic
Soil moisture regime class: udic
Mean annual soil temperature: 38 to 42 degrees F.
Mean summer soil temperature: 52 to 58 degrees F.
Depth to diagnostic feature: 4 to 20 inches (10 to 51 centimeters) to argillic horizon
Thickness of diagnostic feature: 10 to 28 inch (25 to 71 centimeters) thick mollic epipedon; 20 to 54 inch (51 to 137 centimeters) thick argillic horizon
Surface fragments: 1 to 3 percent sandstone stones
Particle-size control section (weighted average):
Clay content: 35 to 50 percent
Rock fragment content: 35 to 85 percent
A horizon(s):
Hue: 10YR
Value: 3 or 4 dry; 2 or 3 moist
Chroma: 1 or 2 dry or moist
Texture: stony loam
Clay content: 20 to 27 percent
Fragment content: 5 to 15 percent sandstone gravel
5 to 15 percent sandstone cobbles
5 to 20 percent sandstone stones
0 to 5 percent sandstone boulders
Reaction: pH 6.6 to 7.3
Bt horizon(s):
Hue: 7.5YR or 10YR
Value: 4 or 5 dry or moist
Chroma: 2 to 4 dry or moist
Texture: very stony clay loam, extremely bouldery clay, very stony clay, extremely stony clay, very bouldery clay
Clay content: 35 to 50 percent
Fragment content: 0 to 23 percent sandstone fine gravel
5 to 20 percent sandstone gravel
15 to 30 percent sandstone cobbles
15 to 30 percent sandstone stones
5 to 30 percent sandstone boulders
Reaction: pH 6.6 to 7.3
COMPETING SERIES: Current competitors are the Embargo, Passar, Redchief, Rooset, and Tellura series.
Embargo: Have lithic contact above 40 inches.
Passar: Have rock fragments derived primarily from rhyolitic tuff.
Redchief: Have lithochromic colors with hue of 5YR or redder.
Rooset: Are calcareous in the lower part of the solum and have continuous horizons of secondary calcium carbonate accumulation.
Tellura: Have less than 5 percent rock fragments 10 inches or more in diameter (stones and boulders), and fragments are also derived mainly from volcanic sources.
GEOGRAPHIC SETTING:
Parent material: colluvium and slope alluvium derived from shale and sandstone
Landform: mountains, hills, and structural benches
Slopes: 5 to 65 percent
Elevation: 6,800 to 9,600 feet
Mean annual temperature: 37 to 41 degrees F
Mean annual precipitation: 18 to 25 inches
Precipitation pattern: Precipitation is relatively evenly distributed throughout the year with a slight peak April to June
Frost-free period: 50 to 80 days.
GEOGRAPHICALLY ASSOCIATED SOILS: These are the Elkhead and Lintim series. The Elkhead soils are moderately well drained and are on floodplains. The Lintim soils have less than 35 percent rock fragments and are on similar landform positions.
DRAINAGE AND PERMEABILITY: well drained, high to very high runoff, slow permeability.
USE AND VEGETATION: The major uses are livestock grazing, wildlife habitat, and recreational purposes. The native plant community is serviceberry, mountain big sagebrush, Idaho fesque, western wheatgrass, needle and thread, Lettermans needlegrass, mountain brome, slender wheatgrass, and snowberry.
DISTRIBUTION AND EXTENT: Northwest, Colorado; LRR E, MLRA 48A; moderate extent.
MLRA SOIL SURVEY REGIONAL OFFICE (MO) RESPONSIBLE: Bozeman, Montana.
SERIES PROPOSED: Routt County, Colorado, Routt County soil survey area, Colorado. The name Evna is coined.
REMARKS:
Diagnostic horizons and features recognized in this pedon are:
Particle-size control section: The zone from 11 to 31 inches. (Bt1 and upper part of Bt2 horizons)
Mollic epipedon: The zone from 0 to 11 inches. (A horizon)
Argillic horizon: The zone from 11 to 65 inches. (Bt1, Bt2, and Bt3 horizons)
Taxonomic Version: classified according to the 9th edition, 2003