LOCATION STEWAH                  ID

Established Series
Rev. BDG-JAL-EMM
11/2013

STEWAH SERIES

The Stewah series consists of deep, well drained soils on side slopes, ridges, and shoulders of foothills and low mountains. They formed in material from fine grained quartzites and siltite of the Libby and Striped Peak formations of the Belt supergroup that is blanketed by a thin mantle of mixed volcanic ash and loess. Saturated hydraulic conductivity is moderately high. Slope ranges from 15 to 55 percent. The average annual temperature is about 45 degrees F. and the average annual precipitation is about 37 inches.

TAXONOMIC CLASS: Coarse-loamy, mixed, superactive, frigid Vitrandic Hapludalfs

TYPICAL PEDON: Stewah ashy silt loam - forested - on a south-facing slope of 43 percent at 3,262 feet elevation. (Colors are for dry soil unless otherwise stated). When described on October 25, 2001, the soil was moist to 40 inches and dry below.

Oi--0 to 1 inch; slightly decomposed needles, twigs, leaves and moss. (0.5 to 1 inch thick)

A--1 to 5 inches; light brownish gray (10YR 6/2) ashy silt loam, very dark brown (7.5YR 2.5/2) moist; moderate very fine and fine granular structure; slightly hard, friable, nonsticky and slightly plastic; many very fine, common fine and medium and few coarse roots; many very fine tubular and common very fine irregular pores; 2 percent paragravel; slightly acid (pH 6.1); abrupt wavy boundary. (2 to 5 inches thick)

Bw--5 to 10 inches; pale brown (10YR 6/3) ashy silt loam, dark brown (7.5YR 3/4) moist; moderate fine and medium subangular blocky structure parting to moderate very fine and fine granular; slightly hard, friable, slightly sticky and slightly plastic; common very fine, fine and medium roots, few coarse roots; many very fine tubular and common very fine irregular pores; 3 percent paragravel; moderately acid (pH 6.0); clear wavy boundary. (0 to 10 inches thick)

Bt1--10 to 16 inches; pale brown (10YR 6/3) silt loam, brown (7.5YR 4/4) moist; moderate fine and medium subangular blocky structure; moderately hard, friable, slightly sticky and moderately plastic; common very fine and fine roots between peds, few medium, coarse and very coarse roots; many very fine tubular and common very fine irregular pores; few faint clay films on surfaces along pores; common faint silt coats on vertical faces of peds and on surfaces along pores; 5 percent paragravel; slightly acid (pH 6.2); clear wavy boundary. (6 to 25 inches thick)

2Bt2--16 to 25 inches; pale brown (10YR 6/3) paragravelly silt loam, dark yellowish brown (10YR 4/4) moist; moderate fine and medium subangular blocky structure; moderately hard, friable, slightly sticky and moderately plastic; common very fine and fine roots between peds; many very fine tubular and common very fine irregular pores; common distinct clay films on vertical faces of peds; common prominent silt coats on vertical faces of peds and on surfaces along pores; 5 percent gravel, 25 percent paragravel; slightly acid (pH 6.1); clear wavy boundary.

2Bt3--25 to 40 inches; very pale brown (10YR 7/4) very paracobbly silt loam, yellowish brown (10YR 5/4) moist; weak fine and medium prismatic structure parting to moderate fine and medium subangular blocky; very hard, firm, moderately sticky and very plastic; common very fine and fine roots between peds, few medium roots; common very fine tubular and irregular pores; common distinct clay films along surfaces of pores and on vertical faces of peds; 5 percent gravel, 15 percent paragravel and 30 percent paracobbles; slightly acid (pH 6.1); clear wavy boundary. (Combined thickness of 2Bt horizons is 0 to 24 inches)

2C1--40 to 52 inches; light yellowish brown (10YR 6/4) extremely paragravelly silt loam, dark yellowish brown (10YR 4/4) moist; massive; moderately hard, friable, nonsticky and slightly plastic; common very fine roots; common very fine tubular pores; 14 percent gravel, 36 percent paragravel and 20 percent paracobbles; moderately acid (pH 5.9); clear wavy boundary.

2C2--52 to 60 inches; light yellowish brown (10YR 6/4) extremely paracobbly silt loam, dark yellowish brown (10YR 4/4) moist; massive; moderately hard, friable, nonsticky and slightly plastic; few very fine roots; 14 percent gravel, 16 percent paragravel and 66 percent paracobbles; moderately acid (pH 5.9); clear wavy boundary. (Combined thickness of 2C horizons is 8 to 21 inches)

2Cr--60+ inches; fractured siltite.

TYPE LOCATION: Latah County, Idaho; about 6 miles north and 4 miles east of Potlatch, Idaho; about 1,650 feet north and 2,200 feet west of the southeast corner of Sec. 2, T42N, R4W; Latitude 47 degrees, 0 minutes, 30 seconds North and Longitude 116 degrees 48 minutes, 5 seconds West; UTM Zone 11 Northing 5206111 meters and Easting 0515101 meters; USGS Sanders Quadrangle.

RANGE IN CHARACTERISTICS:

Solum thickness - 53 to 60 inches
Soil moisture control section - usually dry for less than 45 consecutive days during June to October.
Udic moisture regime.
Average annual soil temperature - 43 to 46 degrees F.
Frigid temperature regime.

A and AB horizons (AB horizon present in some pedons)
Hue - 7.5YR or 10YR moist
Value - 5 or 6 dry, 2 to 3 moist
Chroma - 2 or 3 dry and 2 to 4 moist
Texture - ashy silt loam
Clay content - 8 to 12 percent
Rock fragments - 0 to 5 percent gravel
Reaction - 6.1 to 6.6
Volcanic glass in the 0.02 to 2.0 mm fraction - 5 to 25 percent
Acid-oxalate extractable Al+1/2Fe - 0.4 to 1.0 percent

Bw horizon
Value - 3 or 4 moist
Chroma - 3 or 4 dry or moist
Texture - ashy silt loam
Clay content - 8 to 12 percent
Rock fragments - 0 to 3 percent gravel
Reaction - 5.6 to 6.3
Volcanic glass in the 0.02 to 2.0 mm fraction - 5 to 25 percent
Acid-oxalate extractable Al+1/2Fe - 0.4 to 1.0 percent

E and EB horizons (where present)
Value - 6 dry, 4 moist
Chroma- 3 or 4 dry or moist
Texture - silt loam
Clay content - 11 to 15 percent
Rock fragments - 0 to 25 percent gravel
Pararock fragments - 0 to 3 percent
Reaction - 6.1 to 6.5

Bt horizon
Hue - 7.5YR or 10YR moist
Value - 6 or 7 dry, 4 or 5 moist
Chroma - 2 to 4 dry or moist
Texture - silt loam
Clay content - 12 to 21 percent
Rock fragments - 2 to 20 percent gravel
Reaction - 5.2 to 6.2

2Bt and 2BCt horizons (2BCt horizon present in some pedons)
Hue - 7.5YR or 10YR moist
Value - 6 to 8 dry, 4 to 6 moist
Chroma - 2 to 4 dry, 3 or 4 moist
Texture - silt loam
Clay content - 10 to 18 percent
Rock fragments - 20 to 35 percent gravel, 0 to 30 percent cobbles, 30 to 50 percent total rock fragment content
Reaction - 5.3 to 6.1

2C horizons
Value - 6 to 8 dry, 4 to 6 moist
Chroma - 3 or 4 dry, 4 to 6 moist
Texture - silt loam
Clay content - 8 to 12 percent
Rock fragments - 45 to 65 percent gravel, 0 to 50 percent cobbles, 50 to 90 percent total rock fragment content
Reaction - 5.0 to 5.9

COMPETING SERIES:

Frycanyon soils: are very deep
Rubson soils: are very deep

GEOGRAPHIC SETTING: The Stewah soils are on sideslopes, rigdes, and shoulders of foothills and low mountains. Slopes range from 15 to 55 percent. These soils formed in fine grained quartzites or siltite with a thin mantle of mixed volcanic ash and loess at elevations of 2,575 to 4,000 feet (785 to 1221 meters). The average annual air temperature ranges from 41 to 46 degrees F, with an average annual precipitation of 26 to 39 inches (660 to 991 mm). The frost free season is 85 to 120 days.

GEOGRAPHICALLY ASSOCIATED SOILS: These are the Arson, Chesley and Reggear soils. Arson soils are on sideslopes, shoulders, and ridge summits of foothills and low mountains and have a xeric moisture regime. Chesley soils are on sideslopes and shoulders of foothills and low mountains and have a thick volcanic ash mantle. Reggear soils are on broad interfluves and have a fragipan.

DRAINAGE AND SATURATED HYDRAULIC CONDUCTIVITY: Well drained; medium to rapid runoff; moderately high saturated hydraulic conductivity.

USE AND VEGETATION: These soils are used for timber production, livestock grazing, wildlife habitat, watershed, and recreation. Potential natural vegetation is western redcedar, Douglas-fir, grand fir and western larch with an understory of queencup beadlily, western goldthread, thimbleberry, rocky mountain maple, common snowberry, creeping Oregon grape and Columbian brome.

DISTRIBUTION AND EXTENT: North-central Idaho. The series is not extensive. MLRA 43A.

MLRA SOIL SURVEY REGIONAL OFFICE (MO) RESPONSIBLE: Bozeman, Montana

SERIES ESTABLISHED: Latah County, Idaho, 2013. The name is from a local stream.

REMARKS: Diagnostic horizons and features recognized in this pedon are:

Ochric epipedon - The zone from the soil surface to 5 inches (Oi, and A horizons).

Cambic horizon - The zone from 5 to 10 inches (Bw horizon)

Argillic horizon - The zone from 10 to 40 inches (Bt1, 2Bt2 and 2Bt3 horizons).

Vitrandic feature - The zone from 1 to 10 inches (A and Bw horizons).

Paralithic contact - at a depth of 60 inches

Particle-size control section - The zone from 10 to 30 inches (Bt1, Bt2, and part of the 2Bt3 horizons).

Series reclassified from coarse-silty to coarse-loamy 7/3/2013 based on presence of rock fragments. The series should be investigated to determine if there is a coarse-silty counterpart that needs to be written and delineated separately.

---

National Cooperative Soil Survey
U.S.A.