Established Series
Rev. JPM


The Coal Creek series consists of very deep, poorly drained soils formed in eolian and colluvial materials overlying firm glacial till. Coal Creek soils are in upland depressions and muskeg borders, often along the edges of drainages. Slopes range from 0 to 20 percent. The mean annual temperature is about 35 degrees F., and the average annual precipitation is about 22 inches.

TAXONOMIC CLASS: Coarse-loamy, mixed, superactive, acid Humic Cryaquepts

TYPICAL PEDON: Coal Creek silt loam - on a 5 percent slope under stunted black spruce and willow. (All colors are for moist soil)

Oi--6 to 2 inches; undecomposed mat of leaves, twigs, and grass straw. (1 to 4 inches thick)

Oe--2 inches to 0; dark reddish brown (5YR 2/2) mat of mostly decomposed organic matter mixed with silty material; abrupt smooth boundary. (1 to 2 inches thick)

A--0 to 3 inches; very dark brown (10YR 2/2) silt loam; weak very fine granular structure; very friable; common medium faint mottles of dark grayish brown (2.5Y 4/2); thin irregular streaks of black (5Y 2/1); many roots; very strongly acid; clear smooth boundary. (3 to 9 inches thick)

Cg1--3 to 9 inches; dark olive gray (5Y 3/2) silt loam; weak very thin platy structure; friable; many medium prominent mottles of dark brown (7.5YR 3/2); irregular streaks of dark grayish brown (2.5Y 4/2); common roots; few angular pebbles; very strongly acid; clear smooth boundary. (6 to 14 inches thick)

Cg2--9 to 15 inches; dark greenish gray (5GY 4/1) silt loam; weak very thin platy structure; friable; common medium distinct mottles of olive brown (2.5Y 4/4) and brown (7.5YR 4/4); few roots; few angular pebbles; thin irregular strata of fine sand; very strongly acid; gradual wavy boundary. (6 to 7 inches thick)

2Cg3--15 to 60 inches; dark greenish gray (5GY 4/1) gravelly silt loam; massive; firm; 20 percent gravel, 10 percent cobble up to 6 inches in diameter; thin irregular strata of sand and silty clay loam; gravel increases with depth; very strongly acid. TYPE LOCATION: Homer - Ninilchik Area, Alaska; in the SE 1/4, SE 1/4, Section 23, T.5S., R.13W., Kenai Peninsula.

RANGE IN CHARACTERISTICS: The mat of organic material ranges from 2 to 6 inches thick. Matrix chromas of 2 or less and mottles are present within 20 inches of the surface. Thickness of the umbric epipedon ranges from 9 to 21 inches. Depth to the gravelly 2C horizon ranges from 15 to 30 inches. The coarse fragment content of the control section ranges from 15 to 35 percent. Reaction throughout the profile ranges from very strongly to strongly acid.

The A horizon has hue of 2.5Y or 10YR, moist value of 2 or 3, and moist chroma of 1 or 2.

The C horizons have hue of 2.5Y or 5Y, moist value of 3 or 4, and moist chroma of 1 or 2. Mottling and gley occur throughout. Texture is silt loam with occasional thin stratas of fine sandy loam and silty clay loam.

Texture of the 2C horizon is silt loam with few thin strata of sand, fine sandy loam, and silty clay loam. Coarse fragment content ranges from 20 to 45 percent with 15 to 30 percent gravel and 5 to 15 percent cobble.

COMPETING SERIES: These are the Clam Gulch and Wasilla series of the same subgroup. Clam Gulch and Wasilla soils have greater than 18 percent clay in the control section.

GEOGRAPHIC SETTING: Coal Creek soils are in upland depressions, along muskeg borders, and in concave footslope areas. The soils are often adjacent to drainages. Slopes range from 0 to 20 percent. Coal Creek soils formed in eolian and colluvial materials overlying glacial till. The mean annual temperature ranges from 33 to 37 degrees F. Average annual precipitation ranges from 16 to 28 inches.

GEOGRAPHICALLY ASSOCIATED SOILS: These include the competing Clam Gulch, Slikok, and Torpedo Lake series; and the Kenai, and Naptowne series. The Kenai and Naptowne soils have spodic horizons and are on well drained glacial moraines.

DRAINAGE AND PERMEABILITY: Poorly drained. Runoff is slow on lower slopes and medium on steeper slopes. Seepage from higher areas keeps these soils wet. Permeability is moderate in the surface horizons and moderately slow in the underlying material. The soils on lower slopes near drainages are subject to flooding.

USE AND VEGETATION: Mostly in native vegetation of black spruce, paper birch, willow, alder, grasses, horsetail, low-growing shrubs, and mosses.

DISTRIBUTION AND EXTENT: South-central Alaska. The series is of moderate extent.


SERIES ESTABLISHED: Kenai-Kasilof Area, Alaska, 1960.

REMARKS: Diagnostic horizons and features recognized in this profile include: mottles and matrix chromas of 2 or less from 0 to 60 inches; a cryic temperature regime; an umbric epipedon from 0 to 9 inches; pH is 5.5 (1:1,H2O) or less throughout the profile; texture of the controlsection i silt loam with less than 18 percent clay and more than 15 percent fine sand or coarser.

The Coal Creek series formerly classified as coarse-silty. Classification was revised based on the coarse fragment content of the substratum. A different typical pedon is used due to the incomplete description of the original.

National Cooperative Soil Survey