LOCATION AGATHA IDEstablished Series
TAXONOMIC CLASS: Loamy-skeletal, isotic, frigid Vitrandic Haploxeralfs
TYPICAL PEDON: Agatha ashy silt loam, forested, on a 55 percent east-facing slope at 2,450 feet elevation. Described on August 23, 1978. (Colors are for dry soil unless otherwise noted.)
Oi--0 to 1 inch; undecomposed and slightly decomposed needles and twigs.(0.5 to 1.5 inches thick)
Oa--1 to 2 inches; decomposed organic material. (0 to 1 inch thick)
A--2 to 5 inches; brown (10YR 5/3) ashy silt loam, dark brown (7.5YR 3/4) moist; weak fine granular structure; slightly hard, very friable, slightly sticky and slightly plastic; many very fine, fine, and medium and few coarse roots; many fine interstitial pores; 5 percent gravel; neutral (pH 6.6); clear smooth boundary. (2 to 7 inches thick)
AB--5 to 9 inches; brown (7.5YR 5/4) gravelly ashy silt loam, dark brown (7.5YR 3/4) moist; weak fine subangular blocky structure; slightly hard, very friable, slightly sticky and slightly plastic; many very fine, fine, and medium and few coarse roots many fine tubular pores; 20 percent gravel and 10 percent cobbles; slightly acid (pH 6.4); clear wavy boundary. (0 to 10 inches thick)
Bt1--9 to 20 inches; light brown (7.5YR 6/4) very gravelly silt loam, dark brown (7.5YR 3/4) moist; moderate medium subangular blocky structure; slightly hard, friable, slightly sticky and slightly plastic; common fine and medium and few coarse roots; many fine tubular pores; 30 percent gravel and 10 percent cobbles; few distinct discontinuous clay films lining pores; few clean silt grains on faces of peds; slightly acid (pH 6.4); gradual wavy boundary. (5 to 15 inches thick)
Bt2--20 to 44 inches; light brown (7.5YR 6/4) very cobbly silty clay loam, dark brown (7.5YR 3/4) moist; moderate fine angular blocky structure; very hard, firm, moderately sticky and moderately plastic; common fine and medium roots; many fine tubular pores; 20 percent gravel and 40 percent cobbles; common distinct discontinuous clay films lining pores and on faces of peds; common fine iron and manganese concretions less than 1 mm in diameter; moderately acid (pH 6.0); abrupt wavy boundary. (10 to 24 inches thick)
Bt3--44 to 60 inches; light brown (7.5YR 6/4) very cobbly silty clay loam, dark brown (7.5YR 3/4) moist; moderate medium and coarse angular blocky structure; very hard, firm, moderately sticky and moderately plastic; common fine and medium roots; many fine tubular pores; 30 percent gravel and 30 percent cobbles; many prominent discontinuous clay films lining pores and on faces of peds; many clean silt grains on faces of peds; common fine iron and manganese concretions less than 1 mm in diameter; moderately acid (pH 6.0); abrupt wavy boundary. (6 to 16 inches thick)
R--60 inches; hard basalt bedrock.
TYPE LOCATION: Latah County, Idaho; about 1 mile southeast of Troy, Idaho; about 1,970 feet south and 1,400 feet west of the northeast corner of sec. 18, T. 39 N., R. 3 W. Latitude - 46 degrees, 43 minutes, 33 seconds North; Longitude - 116 degrees, 45 minutes, 13 seconds West; USGS Troy Quadrangle.
RANGE IN CHARACTERISTICS:
Soil moisture - usually dry for 45 to 60 consecutive days, moist in the fall through early summer, dry mid-July through mid-September. Xeric moisture regime.
Average annual soil temperature - 43 to 47 degrees F.
Average summer soil temperature - 48 to 55 degrees F. Frigid temperature regime.
Oe horizons present in some pedons and mixed with 1980 Mt. St. Helens volcanic ash; 0.5 to 1 inch thick
Surface stones - 0 to 3 percent
Depth to bedrock - 40 to 60 inches
Volcanic ash influence 7 to 10 inches thick (surface layers)
Volcanic glass content 5 to 20 percent
Acid-oxalate extr. Al + Fe 0.4 to 0.8 percent
Moist bulk density 1.0 to 1.2 g/cc (estimated)
Phosphate retention 25 to 50 percent
A horizon
Hue - 10YR or 7.5YR
Value - 4 or 5 dry, 2 or 3 moist
Chroma - 2 through 4 dry or moist
Texture - Ashy-SIL, Ashy-L, GR-Ashy-SIL, GRV-Ashy-SIL, GR-Ashy-L
Clay content - 8 to 25 percent
Rock fragments - 0 to 30 percent gravel, 0 to 10 percent cobbles, 0 to 40 percent total rock fragments
Reaction - moderately acid to slightly alkaline
AB or BA horizons
Value - 4 or 5 dry, 3 or 4 moist
Chroma 3 or 4 dry or moist
Texture - SIL, SICL, GR-L, CBV-SIL, GR-Ashy-SIL
Clay content - 12 to 27 percent
Rock fragments - 2 to 40 percent gravel, 0 to 25 percent cobbles, 2 to 45 percent total rock fragments
Reaction slightly acid or neutral
Bw horizon - present in some pedons
Texture - CB-L, CB-SIL
Rock fragments - 15 to 20 percent
Reaction - slightly acid or neutral
Bt horizons
Hue - 10YR or 7.5YR
Value - 4 through 6 dry, 3 through 5 moist
Chroma - 2 through 5 dry, 2 through 4 moist
Texture - GRV-SIL, GR-CL, GRV-L, GRV-CL, GRV-SICL, GRX-SIL, GRX-CL, CBV-SIL, CBV-CL, CBV-L, CBV-SICL, CBV-C, CBX-SIL, CBX-CL, CBX-SICL, STV-SIL, STV-CL, STV-SICL, STX-SIL, STX-CL, STX-SICL, CBX-C
Rock fragments - 15 to 65 percent in the upper part and 45 to 90 percent in the lower part
Base saturation (by sum of cations) - 40 to 75 percent
Clay content 18 to 45 percent
Reaction - strongly acid to neutral
COMPETING SERIES: These are the
Jummer (T),
Nicmar (T),
Outland and
Rasser series.
Jummer soils: 20 to 40 inches to lithic contact (basalt); volcanic ash influence 10 to 22 inches
Nicmar soils: 60 inches or more to bedrock; dry for 60 to 75 consecutive days following summer solstice
Outland soils: 20 to 40 inches to paralithic contact (vesicular andesite); dry for 90 to 110 consecutive days following summer solstice
Rasser soils: 60 inches or more to bedrock; derived from mudflow material
GEOGRAPHIC SETTING: Agatha soils are on benches, escarpments, and canyonsides. These soils formed in colluvium or residuum weathered from basalt with a mixed loess and volcanic ash mantle. Slopes are 5 to 90 percent. Elevations are 1,050 to 5,000 feet. The climate is cool, subhumid with warm, dry summers and cool, moist winters. The average annual precipitation is 24 to 35 inches; average annual air temperature is 40 to 45 degrees F.; and the frost-free season is 70 to 125 days.
GEOGRAPHICALLY ASSOCIATED SOILS: These are the Bobbitt, Dorb, Keuterville, Klickson, Helmer, and Lacy soils. Bobbitt soils have a mollic epipedon, are moderately deep, have a mesic soil temperature regime and are on south-facing slopes. Dorb soils are deep, have a thick mantle of volcanic ash and are on north-facing slopes. Keuterville soils have a mollic epipedon, a mesic soil temperature regime and are on south-facing slopes. Klickson soils have a mollic epipedon and are on north-facing slopes. Helmer soils have a fragipan at depths of 10 to 20 inches, and are on terraces. Lacy soils have a mollic epipedon, have bedrock at depths of 10 to 20 inches, and are on south-facing ridges.
DRAINAGE AND PERMEABILITY: Well drained; rapid to very rapid runoff, moderately slow permeability.
USE AND VEGETATION: These soils are used for timber production, livestock grazing, recreation, and wildlife habitat. Potential natural vegetation is mainly grand fir, western white pine, western larch, Douglas-fir, ponderosa pine, and lodgepole pine, with an understory of mallow ninebark, creambush oceanspray, common snowberry, myrtle pachystima, bald hip rose, heartleaf arnica, Columbia brome, and elk sedge.
DISTRIBUTION AND EXTENT: Northern Idaho. This soil is moderately extensive. MLRA 43A.
MLRA OFFICE RESPONSIBLE: Bozeman, Montana
SERIES ESTABLISHED: Latah County, Idaho, 1979
REMARKS: Diagnostic horizons and features recognized in this pedon are:
Ochric epipedon - The zone from 2 to 9 inches (A and AB horizons)
Argillic horizon - The zone from 20 to 60 inches (Bt2 and Bt3 horizons)
Volcanic ash influence - the zone from 2 to 9 inches (A and AB horizons)
Particle-size control section - The zone from 20 to 40 inches (Bt2 horizon)
ADDITIONAL DATA: Partial laboratory data available for Soil Survey Sample Number: 93ID057-002, NSSL Pedon Number: 93P0585, Latah County, Idaho.