LOCATION IMNAHA OREstablished Series
TAXONOMIC CLASS: Loamy-skeletal, mixed, superactive, frigid Vitrandic Argixerolls
TYPICAL PEDON: Imnaha gravelly ashy silt loam - Rangeland on a 70 percent planar northeast-facing slope at an elevation of 3,600 feet. (Colors are for moist soil unless otherwise noted.)
A1--0 to 5 inches; black (10YR 2/1) gravelly ashy silt loam, very dark grayish brown (10YR 3/2) dry; weak medium subangular blocky structure parting to moderate fine granular; soft, friable, nonsticky and nonplastic; many very fine and fine, and few medium roots; common fine irregular pores; 10 percent gravel and 5 percent cobbles; neutral (pH 6.7); clear wavy boundary.
A2--5 to 17 inches; very dark gray (10YR 3/1) gravelly ashy silt loam, dark grayish brown (10YR 4/2) dry; moderate fine and medium subangular blocky structure; slightly hard, friable, slightly sticky and nonplastic; many very fine and fine, and few medium roots; few fine irregular and common fine tubular pores; 15 percent gravel and 5 percent cobbles; neutral (pH 6.7); clear wavy boundary. (Combined thickness of A horizon is 12 to 20 inches)
Bt1--17 to 21 inches; very dark grayish brown (10YR 3/2) very gravelly silt loam, dark grayish brown (10YR 4/2) dry; moderate fine and medium subangular blocky structure; slightly hard, firm, slightly sticky and slightly plastic; common very fine and fine, and few medium roots; common fine tubular pores; common faint clay films on faces of peds; 25 percent gravel and 10 percent cobbles; slightly acid (pH 6.5); clear wavy boundary.
Bt2--21 to 24 inches; dark brown (10YR 3/3) very gravelly loam, brown (10YR 4/3) dry; moderate fine subangular blocky structure; slightly hard, firm, sticky and slightly plastic; few very fine and fine roots; common fine tubular pores; many faint and few distinct clay films on faces of peds; 30 percent gravel and 10 percent cobbles; slightly acid (pH 6.5); abrupt irregular boundary. (Combined thickness of Bt horizon is 7 to 21 inches)
R--24 inches; basalt bedrock
TYPE LOCATION: Wallowa County, Oregon; 240 feet south and 1580 feet east of the northwest corner of section 34, T.2 S., R.48 E. (Latitude 45 degrees, 21 minutes, 29 seconds N; Longitude 116 degrees, 48 minutes, 43 seconds W.)
RANGE IN CHARACTERISTICS: The soils are usually moist but are dry in all parts between 8 and 30 inches for 60 to 75 days on north slopes and 75 to 90 days on south slopes. The mean annual soil temperature is 42 to 46 degrees F. Depth to bedrock is 20 to 40 inches. The particle-size control section has 18 to 35 percent clay and 35 to 75 percent rock fragments. The mollic epipedon ranges from 20 to 30 inches thick. Volcanic ash influence is 12 to 20 inches. Hue is 10YR to 7.5YR throughout.
The A1 horizon has value of 2 or 3 moist, 3 to 5 dry and chroma of 1 to 3 moist, 2 or 3 dry. It is gravelly ashy silt loam with 10 to 18 percent clay. It has 15 to 30 percent rock fragments with 10 to 25 percent gravel, 5 to 10 percent cobbles, and 0 to 5 percent stones. It has 15 to 30 percent volcanic glass and 0.2 to 0.4 percent acid oxalate extractable aluminum plus one-half iron. Reaction is moderately acid to neutral.
The A2 horizon has value of 2 or 3 moist, 3 to 5 dry and chroma of 1 to 3 moist, 2 or 3 dry. It is gravelly ashy silt loam, gravelly ashy loam, very gravelly ashy silt loam, very gravelly ashy loam, very cobbly ashy silt loam, or very cobbly ashy loam. It has 15 to 45 percent rock fragments with 10 to 30 percent gravel, 5 to 20 percent cobbles, and 0 to 5 percent stones. It has 15 to 30 percent volcanic glass and 0.2 to 0.4 percent acid oxalate extractable aluminum plus one-half iron. Reaction is moderately acid to neutral.
The Bt horizon has value of 3 or 4 moist, 4 or 5 dry and chroma of 2 to 4 moist or dry. It is very gravelly loam, very gravelly silt loam, very gravelly clay loam, very cobbly loam, or extremely stony loam with 18 to 35 percent clay. It has 35 to 75 percent rock fragments with 25 to 40 percent gravel, 10 to 20 percent cobbles, and 0 to 10 percent stones. Reaction is slightly acid to neutral.
COMPETING SERIES: These are the Conwayridge, Ginserly (T), Loganvalley (T), Masonic, Needhill, Roundbarn, Saturday, and Wilt series.
Conwayridge soils - greater than 60 inches to bedrock; mollic epipedon 10 to 14 inches thick; pscs with 10 to 18 percent clay
Ginserly soils - 40 to 60 inches to lithic contact (rhyolite)
Loganvalley soils - greater than 60 inches to bedrock; mollic epipedon 10 to 20 inches thick; has 2Bq horizon
Masonic soils - 20 to 40 inches to paralithic contact (tuff)
Needhill soils - 40 to 60 inches to lithic contact (basalt)
Roundbarn soils - 40 to 60 inches to paralithic contact; dry for 90 to 100 consecutive days
Saturday soils - 40 to 60 inches to lithic contact (basalt)
Skullhollow soils - volcanic ash influence is 7 to 14 inches; this series does not strongly compete with Imnaha.
Wilt soils - dry for 90 to 110 consecutive days; mollic epipedon is 7 to 14 inches thick; volcanic ash influence is 7 to 14 inches thick
Series with a similar classification include the Larabee, Millerflat, Raycreek (T), and Stemilt soils.
Larabee soils - mollic epipedon 10 to 20 inches thick; 5 to 15 percent volcanic glass and 0.4 to 1.0 percent acid oxalate extractable aluminum plus one-half iron in the upper 7 to 14 inches; isotic mineralogy
Millerflat soils - greater than 60 inches to stratified gravelly and sandy alluvium; dry 45 to 60 consecutive days; isotic mineralogy
Raycreek soils - 20 to 40 inches to lithic contact (tuff); 0.4 to 1.0 percent acid oxalate extractable aluminum plus one-half iron in the upper 7 to 14 inches; isotic mineralogy
Stemilt soils - greater than 40 inches to bedrock; mollic epipedon 10 to 18 inches thick; 0.4 to 1.0 percent acid oxalate extractable aluminum plus one-half iron in the upper 7 to 14 inches; isotic mineralogy
GEOGRAPHIC SETTING: Imnaha soils are on stable midslopes of plateaus and canyons. Elevations are 2,800 to 6,200 feet. Slopes are 2 to 90 percent. The soil formed in ash and loess over colluvium derived from basalt. The climate is characterized by cold, wet winters and hot, dry summers. The mean annual precipitation is 15 to 30 inches. The mean annual temperature is 41 to 45 degrees F. The frost-free period is 70 to 100 days.
GEOGRAPHICALLY ASSOCIATED SOILS: These are the Anatone, Bocker, Clearline, and Cherrycreek soils. Anatone soils are 10 to 20 inches deep to basalt bedrock. Bocker soils are less than 10 inches deep to basalt bedrock. Clearline soils lack an argillic horizon. Cherrycreek soils are 40 to 60 inches deep to basalt bedrock and lack an argillic horizon. These soils are located on adjacent side slopes.
DRAINAGE AND PERMEABILITY: Well drained; permeability is moderate.
USE AND VEGETATION: These soils are used for watershed, recreation, livestock grazing, and wildlife habitat. The native vegetation is Idaho fescue, prairie junegrass, Sandberg bluegrass, bluebunch wheatgrass, western hawkweed, yarrow, lupine, twin arnica, Snake River phlox, Wyeth's buckwheat, and arrowleaf balsamroot.
DISTRIBUTION AND EXTENT: Northeastern Oregon; MLRA 9. The soils are of moderate extent.
MLRA SOIL SURVEY REGIONAL OFFICE (MO) RESPONSIBLE: Portland, Oregon
SERIES ESTABLISHED: Wallowa County Area, Oregon 1998. The source of the name is the Imnaha River.
REMARKS: Diagnostic horizons and other features in this pedon are:
Mollic epipedon - the zone from 0 to 24 inches (A1, A2, Bt1, and Bt2 horizons)
Argillic horizon - the zone from 17 to 24 inches (Bt1 and Bt2 horizons)
Vitrandic feature - the zone from 0 to 17 inches (A1 and A2 horizons)
ADDITIONAL DATA: Partial laboratory data available. Reference sample S92OR-063-016 for Wallowa County, Oregon, NSSL, Lincoln, NE, 1/94