LOCATION COBBLANK                AK

Established Series
Rev. MHC/JPM/DLM
02/2022

COBBLANK SERIES

The Cobblank series consists of shallow, well drained soils formed in a thin mantle of silty loess over loamy glacial till and colluvium underlain by consolidated bedrock. Cobblank soils occur on hills. Slopes range from 0 to 20 percent. The mean annual temperature is about 26 degrees F. and the mean annual precipitation is about 16 inches.

TAXONOMIC CLASS: Loamy-skeletal, mixed, superactive Lithic Haplocryepts

TYPICAL PEDON: Cobblank silt loam on an 18 percent slope under open white spruce forest at 2600 feet elevation. (all colors are for moist soil)

Oi--1 inch to 0; dark reddish brown (5YR 3/3) peat; fibrous moss, twigs, and root fibers; abrupt smooth boundary. (1 to 5 inches thick)

A/E--0 to 1 inch; dark brown (10YR 3/3) and dark grayish brown (10YR 4/2) silt loam; weak medium granular structure; very friable, nonsticky and nonplastic; many roots of all sizes; very strongly acid (pH 4.8); abrupt wavy boundary. (1 to 3 inches thick)

2Bw1--1 to 4 inches; brown (7.5YR 4/4) gravelly sandy loam; weak medium subangular blocky structure; very friable, nonsticky and nonplastic; common very fine, fine , and medium roots; 15 percent subangular and subrounded gravel and 5 percent subangular cobble; strongly acid (pH 5.4); gradual wavy boundary. (2 to 8 inches thick)

2Bw2--4 to 10 inches; dark yellowish brown (10YR 4/4) very cobbly sandy loam; weak medium subangular blocky structure; friable, nonsticky and nonplastic; few very fine roots; 20 percent subangular and subrounded gravel and 20 percent subangular cobble; strongly acid (pH 5.4); gradual wavy boundary. (0 to 8 inches thick)

2C--10 to 18 inches; brown (10YR 4/3) very cobbly sandy loam; massive; friable, nonsticky and nonplastic; 20 percent subangular and subrounded gravel and 20 percent subangular cobble; moderately acid (pH 5.6); abrupt irregular boundary. (3 to 11 inches thick)

R--18 inches; consolidated greenstone bedrock.

TYPE LOCATION: Gulkana River Area, Alaska; about 12 miles north of Sourdough; the NE1/4 of the SW1/4 of section 27, T.11N., R.2W., Copper River Meridian.

RANGE IN CHARACTERISTICS: The silty loess mantle ranges in thickness from 1 to 3 inches. The solum is 3 to 10 inches thick. The particle size control section is loamy-skeletal. Depth to bedrock ranges from 10 to 20 inches. Reaction is very strongly acid to moderately acid in the solum and moderately acid or slightly acid in the substratum.

The A horizon or the A part of the A/E horizon has hue of 7.5YR or 10YR; value moist of 2 or 3; chroma moist of 1 through 3. The E part (when present) has value moist of 4 or 5; chroma moist of 2 or 3. Texture is mucky silt loam, silt loam, or loam.

The 2Bw horizon has hue of 7.5YR or 10YR; value moist of 3 or 4; chroma moist of 4 through 6. Texture is loam or sandy loam. Rock fragments range from 15 to 45 percent and include 15 to 45 percent gravel and 0 to 30 percent cobble.

The 2C horizon has hue of 10YR or 2.5Y; value moist of 3 or 4: chroma moist of 2 or 3. Texture is loam, or sandy loam. Rock fragments range from 35 to 70 percent and include 25 to 60 percent gravel and 10 to 40 percent cobble.

COMPETING SERIES: These are the Caseypeak, Cowood, Hechtman, Hotter, Jarbidge, Merino, Pendergrass, Sigbird series. All of these soils lack lithological discontinuties.

GEOGRAPHIC SETTING: The Cobblank soils occur on hills. Slopes range from 0 to 20 percent. Cobblank soils formed in a thin loess mantle overlying very gravelly glacial till and colluvium deposits. The climate is subarctic-continental. Mean annual temperature is about 26 degrees F. Mean annual precipitation is about 16 inches.

GEOGRAPHICALLY ASSOCIATED SOILS:

DRAINAGE AND PERMEABILITY: Well drained. Medium or rapid runoff. Moderate permeability in the mineral soil and variable in the bedrock.

USE AND VEGETATION: Wildlife habitat. Native vegetation includes glandular birch shrub and willow shrub.

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

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

SERIES ESTABLISHED: Gulkana River Area, Alaska, 1999.

REMARKS: Diagnostic horizons and features recognized in this profile include: a cambic horizon from 1 to 10 inches; a loamy-skeletal particle-size control section from 4 to 18 inches; consolidated bedrock at 18 inches; and a cryic temperature regime.

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National Cooperative Soil Survey
U.S.A.