LOCATION FLAT HORN               AK

Established Series
Rev. JWM/JPM
05/2022

FLAT HORN SERIES

The Flat Horn series consists of very deep, somewhat poorly drained soils that formed in a thin mantle of ash influenced loess overlying alluvium. Flat Horn soils occur on stream terraces and outwash plains. Slopes range from 0 to 45 percent. Mean annual temperature is about 34 degrees F., and the average annual precipitation is about 21 inches.

TAXONOMIC CLASS: Coarse-loamy, mixed, superactive Typic Haplocryods

TYPICAL PEDON: Flat Horn silt loam -- on a 2 percent slope under forest vegetation. (All colors for moist soil)

Oe--3 inches to 0; dark reddish brown (5YR 2/2) mat of partially decomposed forest litter and moss; abrupt wavy boundary. (0 to 5 inches thick)

E--0 to 2 inches; gray (10YR 5/1) silt loam; weak thin platy structure; very friable, slightly sticky and nonplastic; many roots; very strongly acid (pH 4.6); abrupt wavy boundary. (1 to 4 inches thick)

Bs1--2 to 3 inches; reddish brown (5YR 4/4) silt loam; weak fine granular structure; very friable, slightly sticky and nonplastic; many fine roots; few fine concretions; very strongly acid (pH 4.6); clear wavy boundary. (1 to 5 inches thick)

Bs2--3 to 8 inches; brown (7.5YR 4/4) and strong brown (7.5YR 5/6) silt loam; weak fine subangular blocky structure; very friable, slightly sticky and nonplastic; common roots; strongly acid (pH 5.2); abrupt wavy boundary. (0 to 10 inches thick)

Eb--8 to 9 inches; grayish brown (2.5Y 5/2) silt loam; weak fine subangular blocky structure; friable, slightly sticky and nonplastic; common roots; strongly acid (pH 5.2); abrupt broken boundary. (0 to 2 inches thick)

2Bsb--9 to 15 inches; dark yellowish brown (10YR 4/4) fine sandy loam; patches of brown (7.5YR 4/4) and yellowish brown (10YR 5/4) silt and fine sand; weak medium subangular blocky structure; friable, nonsticky and nonplastic; common roots; strongly acid (pH 5.2); clear smooth boundary. (0 to 9 inches thick)

3C1--15 to 21 inches; olive brown (2.5Y 4/4) fine sand stratified with silt; strata are well sorted and range from 1/4 to 2 inches thick; fine sand is single grained and loose, silt has weak medium subangular blocky structure; friable, nonsticky and nonplastic; few roots; strongly acid (pH 5.2); gradual wavy boundary. (4 to 12 inches thick)

3C2--21 to 60 inches; olive (5Y 4/3) fine sand stratified with silt; strata are well sorted and range from 1/2 to 4 inches thick; fine sand is single grained and loose, silt is massive; friable, nonsticky and nonplastic; few weakly cemented streaks of dark yellowish brown (10YR 4/4) in fine sand strata; few roots to 30 inches, none below; strongly acid (pH 5.2).

TYPE LOCATION: Susitna Valley Area, Alaska; 300 yards north of Kroto Creek; NW1/4, SW1/4 of section 22, T.20N., R.6W., Seward Meridian.

RANGE IN CHARACTERISTICS: The thickness of the ash influenced eolian deposits ranges from 8 to 14 inches thick. The solum ranges from 8 to 24 inches thick. The exchange complex of the eolian mantle is dominated by amorphous material. Textures in the control section include silt loam, fine sandy loam, and fine sand stratified with silt. The weighted average particle size class of these materials is coarse-loamy. There are less than 15 percent coarse fragments throughout the control section. Reaction throughout the profile ranges from very strongly acid to medium acid. The E horizon has hue ranging from 5YR to 10YR; value from 3 through 7 moist; and chroma of 1 or 2 moist.

The Bs horizons have hue ranging from 5YR to 10YR; value from 3 through 5 moist; and chroma from 3 through 6 moist.

The Eb horizon is absent in some pedons.

The 2Bsb horizon, where present, has hue of 7.5YR or 10YR; value of 4 or 5 moist; and chroma of 3 or 4 moist.

The 3C horizon has hue of 2.5Y or 5Y; value moist of 4 or 5; and chroma moist of 3 or 4.

COMPETING SERIES: These are the Barlow, Hartnit, Oso, and Timberly series. Barlow and Timberly series do not have amorphous material in the series control section. Hartnit soils have a mean annual soil temperature of 42 to 44 degrees F and Bsh horizons. Oso soils are 20 to 40 inches to bedrock.

GEOGRAPHIC SETTING: The Flat Horn series occur on stream terraces. They formed in an admixture of eolian silt and volcanic ash overlying medium textured alluvium. The climate is transitional between maritime and continental with the average annual precipitation ranging from 13 to 30 inches. Mean annual temperature ranges from 33 to 36 degrees F. Slopes range from 0 to 45 percent.

DRAINAGE AND PERMEABILITY: Well drained. Moderate permeability. Slow to rapid runoff.

USE AND VEGETATION: Used for timber production, wildlife habitat, recreation, hay and pastureland, and cropland. Native vegetation is white spruce and paper birch.

DISTRIBUTION AND EXTENT: Southcentral Alaska. The series is of moderate extent.

SOIL SURVEY REGIONAL OFFICE (SSRO) RESPONSIBLE: WASILLA, ALASKA

SERIES ESTABLISHED: Matanuska Valley Area, Alaska, 1966.

REMARKS: Diagnostic horizons and features recognized in this profile are:
a.spodic horizon from 2 to 8 inches; a weighted average particle size class of coarse-loamy from 10 to 40 inches; cryic temperature regime. The Flat Horn series formerly classified as medial over coarse- loamy. Medial material, however, does not extend more than 4 inches into the control section.

---

National Cooperative Soil Survey
U.S.A.