LOCATION SHAWMOUNT IDEstablished Series
TAXONOMIC CLASS: Loamy-skeletal, mixed, superactive, mesic Aridic Argixerolls
TYPICAL PEDON: Shawmount gravelly sandy loam -- on a convex northwest-facing slope of 23 percent at 3,420 feet elevation in rangeland. When described on September 3, 1995, the soil was dry throughout. (Colors are for air-dry soil unless otherwise stated.)
A--0 to 3 inches; grayish brown (10YR 5/2) gravelly sandy loam, very dark grayish brown (10YR 3/2) moist; moderate fine granular structure; soft, very friable, slightly sticky and slightly plastic; many very fine and fine, few medium and coarse roots; many very fine and fine, few medium tubular and irregular pores; 15 percent gravel, 5 percent cobbles; neutral (pH 6.6); clear smooth boundary. (2 to 7 inches thick)
AB--3 to 10 inches; brown (10YR 5/3) gravelly sandy loam, dark brown (10YR 3/3) moist; weak fine subangular blocky structure; slightly hard, very friable, slightly sticky and slightly plastic; many very fine and fine, few medium and coarse roots; many very fine and fine, few medium tubular pores; 20 percent gravel, 5 percent cobbles; neutral (pH 6.7); clear wavy boundary. (0 to 10 inches thick)
Bt1--10 to 16 inches; yellowish brown (10YR 5/4) very gravelly sandy clay loam, dark yellowish brown (10YR 3/4) moist; moderate fine subangular blocky structure; hard, friable, slightly sticky and slightly plastic; common very fine and fine, few medium roots; common very fine and fine, few medium tubular pores; common distinct clay films on faces of peds, in pores and bridging sand grains; 40 percent gravel, 10 percent cobbles; neutral (pH 6.7); clear wavy, boundary.
Bt2--16 to 26 inches; yellowish brown (10YR 5/4) very gravelly sandy clay loam, dark yellowish brown (10YR 3/4) moist; moderate fine subangular blocky structure; very hard, friable, slightly sticky and slightly plastic; common very fine and fine roots; common very fine and fine, few medium tubular pores; many distinct clay films on faces of peds, in pores and bridging sand grains; 40 percent gravel, 10 percent cobbles; slightly acid (pH 6.5); gradual wavy boundary.
Bt3--26 to 38 inches; yellowish brown (10YR 5/4) very gravelly sandy clay loam, dark yellowish brown (10YR 3/4) moist; moderate fine subangular blocky structure; hard, very friable, slightly sticky and slightly plastic; few very fine and fine roots; common very fine and fine tubular pores; common distinct clay films on faces of peds, in pores and bridging sand grains; 45 percent gravel, 15 percent cobbles; slightly acid (pH 6.5); clear wavy boundary. (combined Bt horizon - 13 to 30 inches thick)
E&Bt--38 to 48 inches; (E material - 95% of horizon) light yellowish brown (10YR 6/4) extremely gravelly sandy loam, dark yellowish brown (10YR 4/4) moist; massive; hard, very friable, nonsticky and nonplastic; few very fine and fine roots; common very fine and fine tubular pores; 60 percent gravel, 15 percent cobbles; neutral (pH 6.6); (Bt material) continuous lamellae; yellowish brown (10YR 5/4) sandy clay loam, dark yellowish brown (10YR 3/4) moist; 2 to 10 mm thick, 2 to 5 inches apart; many distinct clay films bridging sand grains; clear wavy boundary. (6 to 18 inches thick)
C--48 to 60 inches; very pale brown (10YR 7/4) extremely gravelly coarse sandy loam, yellowish brown (10YR 5/4) moist; massive; slightly hard, very friable, nonsticky and nonplastic; few very fine and fine roots; many very fine and fine irregular pores; 60 percent gravel, 20 percent cobbles; neutral (pH 6.8).
TYPE LOCATION: Ada County, Idaho; about 1 mile northwest of Lucky Peak Dam; 1,750 feet south and 1,950 feet east of the northwest corner of section 2, T.2 N., R.3 E.; USGS Lucky Peak Quadrangle; Latitude - 43 degrees, 32 minutes, 25 seconds N. and Longitude - 116 degrees, 03 minutes, 52 seconds W.; NAD 27.
RANGE IN CHARACTERISTICS:
Mollic epipedon thickness - 7 to 12 inches
Depth to base of argillic horizon - 20 to 40 inches
Particle-size control section - 18 to 30 percent clay; 35 to 65 percent rock fragments
Reaction - slightly acid or neutral
Moisture control section - moist less than 90 consecutive days when the soil temperature is greater than 47 degrees F.
Average annual soil temperature - 50 to 53 degrees F.
A horizon
Value - 4 or 5 dry, 2 or 3 moist
Chroma - 2 or 3 dry or moist
Rock fragments - 0 to 5 percent stones, 5 to 10 cobbles, 15 to 30 gravel and 15 to 35 total
Bt horizon
Value - 5 or 6 dry, 3 or 4 moist
Chroma - 3 or 4 dry or moist
Texture - SL, L, CL or SCL
Clay content - 18 to 30 percent
Rock fragments - 0 to 5 percent stones, 5 to 15 cobbles, 35 to 50 gravel and 35 to 60 total
E&Bt horizon
Clay content (weighted average) - 5 to 15 percent
Rock fragments (weighted average) - 50 to 85 percent
- E material (greater than 90 percent)
Value - 6 or 7 dry, 4 or 5 moist
Texture - SL, COSL, LS or LCOS
Clay content - 5 to 15 percent
Rock fragments - 0 to 5 percent stones, 5 to 20 cobbles, 35 to 75 gravel and 50 to 85 total
- Bt material (lamellae)
Hue - 7.5YR or 10YR
Value - 5 or 6 dry, 3 or 4 moist
Chroma - 4 through 6 dry or moist
Texture - SL or SCL
Clay content - 12 to 22 percent
Thickness - 2 to 15 mm
Separation - 1 to 8 inches
C horizon
Value - 6 or 7 dry, 4 or 5 moist
Texture - SL, LS, COSL or LCOS
Clay content - 4 to 15 percent
Rock fragments - 0 to 10 percent stones, 5 to 30 cobbles, 35 to 75 gravel and 60 to 85 total
COMPETING SERIES: These are the Ashue, Badena, Badenaugh, Eaglerock, Gitabyte (T), Grinrod, Ister, Lemm, Leviathan, Nosrac, Oest, Searles, Searvar, Shree, Shroe, Trid and Tristan series. Ashue soils have extremely gravelly or extremely cobbly sand textures in the 2C horizon at depths greater than 30 inches and do not have lamellae below the argillic horizon. Badena soils are 20 to 36 inches to sandy-skeletal material, have a mean annual soil temperature of 47 to 50 degrees F. and Bt horizons that are strongly alkaline with over 60 percent rock fragments. Badenaugh and Leviathan soils have Bt horizons extending to depths of greater than 60 inches. Eaglerock, Gitabyte, Grinrod, Ister, Searles, Searvar and Trid soils are 20 to 40 inches deep to lithic or paralithic contact. Nosrac soils have a mean annual soil temperature of 47 to 50 degrees F., Bt horizons that have less than 45 percent sand with a base greater than 50 inches deep and lack lamellae below the argillic horizon. Oest soils do not have lamellae below the argillic horizon. Lemm soils have less than 18 percent clay in the Bt horizon. Shree soils do not have lamellae below the argillic horizon. Shroe soils have 35 to 45 percent clay in the upper Bt horizon, have 2C horizons of lacustrine sediment origin, and do not have lamellae below the argillic horizon. Tristan soils are 40 to 60 inches deep to bedrock.
GEOGRAPHIC SETTING: Shawmount soils are nearly level to very steep on flood-plain steps, stream terraces, relict lakebed escarpments and eroded fan remnants at elevations of 2,500 to 4,000 feet. Slopes range from 1 to 65 percent. These soils formed in alluvium and colluvium from igneous rocks (dominantly granitic). Average annual precipitation ranges from 13 to 16 inches. Average annual temperature ranges from 48 to 51 degrees F. Frost-free period is 130 to 150 days.
GEOGRAPHICALLY ASSOCIATED SOILS: These are the Ada, Adelmann, Cranegulch and Flofeather soils. Ada, Adelmann and Cranegulch soils are clayey and are on dissected fan remnants. Flofeather soils are coarse-loamy and on nearly level flood plain steps.
DRAINAGE AND PERMEABILITY: Well drained; very slow to rapid runoff; moderate permeability.
USE AND VEGETATION: Shawmount soils are used mainly for rangeland. Native vegetation is basin big sagebrush, antelope bitterbrush, bluebunch wheatgrass and Thurber needlegrass. Some areas are used for homesites.
DISTRIBUTION AND EXTENT: West-central and southwestern Idaho. MLRA 10 and 11. Shawmount soils are not extensive.
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 0 to 10 inches (A and AB horizons)
Argillic horizon - zone 10 to 38 inches (Bt1, Bt2 and Bt3 horizons)
Particle-size control section - zone 10 to 30 inches
Soil moisture regime - aridic bordering on xeric
These soils are drier than other Xerolls in the region under similar precipitation due to early runoff and extended period of high evapotranspiration.