LOCATION AGATHA ID

Established Series
Rev. CJW-BDG-EMM
05/2013

AGATHA SERIES

The Agatha series consists of deep, well drained soils on benches, plateaus, escarpments, and canyonsides. They formed in colluvium or residuum weathered from basalt with a mixed loess and volcanic ash mantle. Saturated hydraulic conductivity is moderately high. Slopes are 5 to 90 percent. The average annual precipitation is about 30 inches, and the average annual air temperature is about 44 degrees F.

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.
Average annual soil temperature - 43 to 47 degrees F.
Average summer soil temperature - 48 to 55 degrees F.
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 12 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 - 0.80 to 1.50 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 to 4 dry or moist
Texture - ashy-silt loam or ashy-loam
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 - loam, silt loam, ashy-silt loam or silty clay loam
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 - strongly acid to neutral

Bw horizon - present in some pedons
Texture - loam or silt loam
Rock fragments - 15 to 20 percent
Reaction - slightly acid or neutral

Bt horizons
Hue - 10YR or 7.5YR
Value - 4 to 6 dry, 3 to 5 moist
Chroma - 2 to 5 dry, 2 to 4 moist
Texture - loam, silt loam, clay loam, silty clay loam, or clay
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:
Bennettcreek soils: 20 to 40 inches to lithic contact (basalt or tuffbreccia)
Jummer soils: 20 to 40 inches to lithic contact (basalt); volcanic ash influence 10 to 22 inches
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
Stevensgulch: greater than 60 inches to a lithic contact; formed in colluvium and residuum in relict alluvial and lacustrine deposits with a minor amount of volcanic ash

GEOGRAPHIC SETTING: Agatha soils are on benches, plateaus, 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 (328 to 1524 meters). The climate is cool, subhumid with warm, dry summers and cool, moist winters. The average annual precipitation is 24 to 41 inches (600 to 1040 mm); average annual air temperature is 40 to 46 degrees F.; and the frost-free season is 70 to 130 days.

GEOGRAPHICALLY ASSOCIATED SOILS: These are the Bobbitt, Dorb, Keuterville, Klickson, Threebear, 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. Threebear soils have a fragipan at depths of 20 to 40 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 SATURATED HYDRAULIC CONDUCTIVITY: Well drained; moderately high saturated hydraulic conductivity.

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. MLRAs 43A and 9.

MLRA SOIL SURVEY REGIONAL OFFICE (MO) 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)

The Agatha soils have a frigid soil temperature regime and a xeric soil moisture regime.

ADDITIONAL DATA: Partial laboratory data available for Soil Survey Sample Number: 93ID057-002, NSSL Pedon Number: 93P0585, Latah County, Idaho.

National Cooperative Soil Survey
U.S.A.