LOCATION CENTUU                  AK

Established Series
SDB/MJS
08/2025

CENTUU SERIES

Depth class: very deep
Drainage class: well drained
Parent material: silty loess over sandy and gravelly alluvium
Landscape: mountains
Landform: river valleys and alluvial fans
Slopes: 2 to 10 percent
Mean annual precipitation: about 350 mm (14 in)
Mean annual air temperature: about -1 degrees C. (30 degrees F)
Frost-free period: 32 to 103 days

TAXONOMIC CLASS: Coarse-loamy over sandy or sandy-skeletal, mixed, superactive Cumulic Haplocryolls

TYPICAL PEDON: Centuu highly organic silt loam in a white spruce balsam poplar forest on a north facing linear, linear alluvial fan on a slope of 4 percent at an elevation of 217m (710 ft).

Oe--0 to 8 cm (0 to 3 in); moderately decomposed plant material, dark brown (7.5YR 3/2) moist; common very fine, fine, medium, coarse, and very coarse roots throughout; noneffervescent; slightly alkaline (pH 7.6); clear smooth boundary. (6 to 12 cm, 2 to 5 in).

A1--8 to 23 cm (3 to 9 in); silt loam, black (7.5YR 2.5/1) moist; moderate medium granular structure; very friable, nonsticky, nonplastic; common very fine, fine, medium, coarse and very coarse roots throughout; neutral (pH 6.8); gradual smooth boundary.

A2--23 to 50 cm (9 to 20 in); silt loam, very dark brown (10YR 2/2) moist; moderate medium subangular blocky structure; friable, nonsticky, nonplastic; common very, fine, medium, and coarse roots throughout; 15 percent fine dendritic brown (10YR 5/3) masses of reduced iron with clear boundaries around rock fragments and 20 percent medium irregular strong brown (7.5YR 5/6) masses of oxidized iron with clear boundaries in matrix; neutral (pH 7.2); abrupt smooth boundary; combined thickness (40 to 60 cm, 16 to 24 in)

2C--50 to 150 cm (20 to 59 in); extremely gravelly loamy sand, olive gray (5Y 4/2) moist; single grain; loose, nonsticky, nonplastic; common fine roots top of horizon; 5 percent cobbles by volume, 25 percent gravel by volume, 45 percent fine gravel by volume; noneffervescent; slightly alkaline (pH 7.4). (78 to 104 cm, 31 to 41 in).

TYPE LOCATION: North Copper River Soil Survey Area, Alaska; latitude 61.64911, longitude -144.67706, UTM 6837287.39 north and UTM 623047.97 east, zone 6, Datum WGS84.

RANGE IN CHARACTERISTICS:

Soil moisture regime: udic
Soil temperature regime: cryic
Mean annual soil temperature: -1 to 5 degrees C. (30 to 41 degrees F)
Thickness of organic material: 6 to 12 cm (2 to 5 in)
Thickness of mollic epipedon: 40 to 60 cm (16 to 24 in)

Oi and Oe horizon:
Hue: 7.5YR or 10YR
Value: 2 to 3
Chroma: 1 to 3
Texture: Moderately decomposed organic material or slightly decomposed organic material
Organic matter: 60 to 90 percent
Reaction class: very strongly acid to slightly acid (pH 4.5 to 6.5)

A horizon:
Hue: 10YR or 2.5Y
Value: 2 to 3
Chroma: 1 to 2
Texture: Silt loam
Sand: 20 to 45 percent
Silt: 50 to 76 percent
Clay: 2 to 10 percent
Reaction class: neutral (pH 6.6 to 7.3)

C horizon:
Hue: 10YR or 5Y
Value: 3 to 5
Chroma: 2 to 3
Texture: very gravelly loamy sand, very gravelly coarse sand, extremely gravelly loamy sand
Sand: 70 to 99 percent
Silt: 0 to 29 percent
Clay: 1 to 5 percent
Rock fragments: 40 to 75 percent
Reaction class: slightly alkaline (pH 7.4 to 7.8)

Some pedons have a Bw horizon that is either part of, or beneath, the mollic epipedon. This horizon has a texture of silt loam or silty clay loam, tend to have a hue of 10YR or 2.5YR, value between 3 and 5, and a chroma of 1 to 3. Horizon thickness 20 to 50 cm (8 to 20 in).

COMPETING SERIES: These are the Kouwegok soils.
Kouwegok soils have pH values lower than 6 in the AB and 2CA horizons and mean annual soil temperatures below -1 degree C (30 F).

GEOGRAPHIC SETTING:
Elevation: 100 to 700 meters (330 to 2295 ft)
Parent material: silty loess over sandy and gravelly alluvium
Landform: river valleys and alluvial fans
Slopes: 2 to 10 percent
Mean annual precipitation: 300 to 800 mm (12 to 31 in)
Mean annual air temperature: -4 to 1 degrees C. (25 to 34 degrees F)
Frost free period: 32 to 103 days

GEOGRAPHICALLY ASSOCIATED SOILS: These are the Ahtell, Chelina, Kluna, Mcclaren, Nizina, and Stibnite soils
Ahtell soils are well drained, lack permafrost, have folistic and umbric epipedons, and occur on hills.
Chelina soils are well drained, lack a mollic epipedon, and occur on the ancient shorelines of lake plains.
Kluna soils are well drained, have stratified horizons of sandy and silty alluvium, and occur on stream terraces and floodplains.
Mclaren soils are well drained, lack a mollic epipedon, and occur on stream terraces and in river valleys.
Nizina soils lack the thick loess cap and mollic epipedon, and occur on floodplains.
Stibnite soils are well drained, have a cambic horizon, and occur in till plains, mountains, kames and kettles.

DRAINAGE AND SATURATED HYDRAULIC CONDUCTIVITY:
Drainage class: well
Saturated Hydraulic Conductivity: Very high in the O and C horizons, moderately high in the A horizon.
Permeability: Very rapid in the O and C horizons, moderately rapid in the A horizon.
Runoff: Low

USE AND VEGETATION:
Use: wildlife habitat, recreation, and subsistence
Native vegetation: white spruce, balsam poplar, squashberry and moss

DISTRIBUTION AND EXTENT: MLRA 228 Interior Alaska mountains.
Extent: limited

SOIL SURVEY REGIONAL OFFICE (SSRO) RESPONSIBLE: Wasilla, Alaska

SERIES ESTABLISHED: North Copper River Soil Survey, Alaska, 2024.

REMARKS: Diagnostic features and horizons recognized in this profile include:

Particle-size control section: 33 to 108 cm (13 to 43 in)

Mollic epipedon: 8 to 50 cm (3 to 20 in) (A1 and A2 horizons)

Lithologic discontinuity: 50 to 150 cm (20 to 59 in) (2C horizon)

ADDITIONAL DATA:

User pedon Id: 2018AK261300

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National Cooperative Soil Survey
U.S.A.