LOCATION MIDDLEFORK IDEstablished Series
TAXONOMIC CLASS: Fine-loamy, mixed, superactive, frigid Ultic Argixerolls
TYPICAL PEDON: Middlefork loam, forested -- on an 11 percent convex east-facing slope at 3,350 feet elevation. When described on October 20, 1997, the soil was moist to 4 inches and dry below. (Colors are for air-dry soil unless otherwise noted.)
Oi--0 to 1 inch; slightly decomposed forest litter.
A1--1 to 4 inches; dark grayish brown (10YR 4/2) loam, very dark brown (10YR 2/2) moist; weak fine subangular blocky structure parting to moderate fine granular; soft, very friable, slightly sticky and slightly plastic; common very fine and fine, few medium and coarse roots; many very fine and fine irregular pores; slightly acid (pH 6.4); clear smooth boundary.
A2--4 to 12 inches; grayish brown (10YR 5/2) loam, very dark grayish brown (10YR 3/2) moist; weak fine subangular blocky structure; slightly hard, very friable, slightly sticky and slightly plastic; common very fine and fine, few medium and coarse roots; many very fine and fine irregular pores; 5 percent fine gravel; slightly acid (pH 6.3); clear smooth boundary. (combined A horizon - 10 to 20 inches thick)
BA--12 to 15 inches; pale brown (10YR 6/3) loam, brown (10YR 4/3) moist; moderate fine and medium subangular blocky structure; hard, very friable, slightly sticky and slightly plastic; common very fine and fine, few medium and coarse roots; common very fine and fine tubular pores; 5 percent fine gravel; moderately acid (pH 6.0); clear wavy boundary. (0 to 15 inches thick)
Bt1--15 to 32 inches; pale brown (10YR 6/3) loam, brown (10YR 4/3) moist; moderate medium subangular blocky structure; hard, friable, slightly sticky and slightly plastic; few very fine, fine, medium and coarse roots; common very fine and fine tubular pores; few distinct clay films in pores; 5 percent fine gravel; moderately acid (pH 5.9); gradual wavy boundary. (8 to 24 inches thick)
Bt2--32 to 47 inches; pale brown (10YR 6/3) clay loam, brown (10YR 4/3) moist; strong medium and coarse subangular blocky structure; very hard, firm, moderately sticky and moderately plastic; few very fine, fine and medium roots; common very fine and fine tubular pores; common distinct clay films on faces of peds and in pores; light yellowish brown (10YR 6/4) continuous lamellae 4 to 10 mm thick and 2 to 4 inches apart; 5 percent fine gravel; moderately acid (pH 5.7); gradual wavy boundary. (10 to 30 inches thick)
Bt3--47 to 60 inches; light gray (10YR 7/2) sandy clay loam, grayish brown (10YR 5/2) moist; moderate medium and coarse subangular blocky structure; very hard, firm, slightly sticky and slightly plastic; few very fine and fine roots; common very fine and fine irregular pores; few distinct clay films on faces of peds and in pores; light yellowish brown (10YR 6/4) discontinuous lamellae 4 to 10 mm thick and 6 to 12 inches apart with variable orientation; 10 percent gravel; moderately acid (pH 5.8).
TYPE LOCATION: Boise County, Idaho; about 3 miles north of Crouch; 1,400 feet north and 150 feet east of the southwest corner of section 27, T.10 N., R.4 E.; USGS Pyle Creek Quadrangle; Latitude - 44 degrees, 10 minutes, 03 seconds N. and Longitude - 115 degrees, 58 minutes, 37 seconds W.; NAD 83.
RANGE IN CHARACTERISTICS:
Thickness of mollic epipedon - 10 to 20 inches
Depth to base of argillic horizon - 40 to 60 inches or more
Depth to bedrock - 60 inches or more
Base saturation - 50 to 75 percent in some part between 10 and 30 inches
Particle-size control section - 20 to 32 percent clay; 0 to 15 percent rock fragments; greater than 30 percent fine sand or coarser
Moisture control section - dry 45 to 75 consecutive days following the summer solstice
Average annual soil temperature - 44 to 47 degrees F.
A horizon
Hue - 7.5YR or 10YR
Value - 4 or 5 dry, 2 or 3 moist
Chroma - 2 or 3 dry or moist
Rock fragments - 0 to 10 percent gravel
Reaction - moderately acid or slightly acid
Bt horizon
Hue - 7.5YR or 10YR
Value - 6 or 7 dry, 4 or 5 moist
Chroma - 3 or 4 dry or moist
Texture - L, SCL or CL
Clay content - 20 to 32 percent
Lamellae - 2 to 10 mm thick; 2 to 15 inches apart
Rock fragments - 0 to 20 percent gravel
E&Bt horizons are present in the lower part of some pedons
COMPETING SERIES: These are the Carmack, Elkcreek, Johnson, Mojo, Molyneux, Moolmool (T), Muldoon, Simonton, Skelter and Suloaf series. Carmack soils have 15 to 30 percent sand coarser than very fine sand in the particle-size control section and do not have lamellae. Elkcreek and Mojo soils are 20 to 40 inches deep to bedrock and in addition, Mojo soils do not have an activity class family designated. Johnson soils do not have lamellae, are sometimes less than 40 inches deep to bedrock and are formed in loess and residuum (see remarks). Moolmool soils have 15 to 35 percent rock fragments in the particle-size control section. Muldoon soils have a duripan (Bqm horizon) and do not have an O horizon. Molyneux soils do not have an O horizon and have argillic horizons that are slightly acid or neutral. Simonton soils do not have an O horizon and do not have lamellae. Skelter soils do not have an O horizon, have extremely acid to strongly acid stratified discontinuous lithology below the argillic horizon and are dry 90 to 120. Suloaf soils have 15 to 30 percent sand coarser than very fine sand in the particle-size control section and are 40 to 60 inches deep to bedrock.
GEOGRAPHIC SETTING: Middlefork soils are strongly sloping to steep on dissected fan remnants and outwash terrace remnants at elevations of 3,050 to 5,250 feet. These soils formed in lacustrine sediments derived from igneous rocks and fine pyroclastic materials. Slopes range from 8 to 50 percent. Average annual precipitation is 20 to 30 inches. Average annual temperature is 42 to 45 degrees F. Frost-free period is 60 to 90 days.
GEOGRAPHICALLY ASSOCIATED SOILS: These are the Charters, Hellake, Pinney and Zeb soils. Charters soils do not have argillic horizons and occur on more exposed geomorphic positions. Hellake soils are mesic and occur on south-facing slopes. Pinney soils have pachic epipedons and occur on steeper north-facing slopes. Zeb soils are skeletal and occur on convex summits and shoulders.
DRAINAGE AND PERMEABILITY: Well drained; medium to rapid runoff; moderately slow permeability.
USE AND VEGETATION: Middlefork soils are used mainly for timber production and woodland grazing. Some areas are used for homesites. Native vegetation is Douglas-fir, ponderosa pine, common snowberry, mallow ninebark and Geyers (elk) sedge.
DISTRIBUTION AND EXTENT: West-central Idaho. MLRA 43b and 44. Middlefork soils are of small extent.
MLRA SOIL SURVEY REGIONAL OFFICE (MO) RESPONSIBLE: Portland, Oregon
SERIES ESTABLISHED: Boise County Area, Idaho, Parts of Ada and Boise Counties, 2005.
REMARKS: Diagnostic horizons and features recognized in this pedon:
Mollic epipedon - zone from 1 to 12 inches (A1 and A2 horizons)
Argillic horizon - zone from 15 to 60 inches (Bt1, Bt2 and Bt3 horizons)
Particle-size control section - zone from 15 to 35 inches
Soil moisture regime - xeric
All depths related to diagnostic horizons and features listed in the range of characteristics are measured from the top of the first mineral horizon.
Further investigations are needed to confirm the typical depth class and soil temperature regime of the Johnson series. Presence or absence of discontinuous lamellae may not be adequate criteria for series separation. However, soil genesis of the two series is a key difference: residual material vs. lacustrine deposits.
ADDITIONAL DATA: This pedon has partial laboratory analysis, reference sample no. S98ID-015-003 (Pedon no. 99P59), NSSL, Lincoln, NE