LOCATION ROCKLAKE AK

Established Series
SDB/MJS
08/2025

ROCKLAKE SERIES

Depth class: very deep, shallow to bedrock, lithic
Drainage class: well drained
Parent material: silty noncalcareous loess over gravelly colluvium
Landscape: Glacially modified mountains and hills
Landform: hillslopes and mountain slopes
Slope: 5 to 30 percent
Mean annual precipitation: about 400 mm (16 in)
Mean annual air temperature: about -1.5 degrees C (29 F)
Frost-free period: 32 to 103 days

TAXONOMIC CLASS: Loamy-skeletal, mixed, superactive, nonacid Lithic Cryorthents

TYPICAL PEDON: Rocklake silt loam in a black spruce community on a north facing simple, convex slope of 22 percent at an elevation of 384m (1110 ft).

Oe--0 to 11 cm (0 to 4 in); moderately decomposed plant material, dark brown (7.5YR 3/2) moist; common very fine, fine, medium, and coarse roots throughout; slightly acid (pH 6.3); clear wavy boundary (6 to 13 cm, 2 to 5 in)

A--11 to 18 cm (4 to 7 in); silt loam, black (7.5YR 2.5/1) moist; moderate medium granular structure; soft, very friable, nonsticky, nonplastic; nonsmeary; common very fine and fine roots throughout; neutral (pH 6.6); clear wavy boundary (5 to 11 cm, 2 to 4 in)

Bw--18 to 31 cm (7 to 12 in); silt loam, 85 percent dark grayish brown (10YR 4/2) and 10 percent very dark grayish brown (10YR 3/2) and 5 percent black (10YR 2/1) moist; weak medium subangular blocky structure; soft, very friable, nonsticky, nonplastic; nonsmeary; common medium roots; 5 percent medium distinct irregular weakly coherent cemented (10yr 5/1) masses of reduced iron with clear boundaries in matrix and 7 percent medium distinct irregular weakly coherent cemented (10yr 4/6) masses of oxidized iron with clear boundaries in matrix; neutral (pH 6.8); clear irregular boundary (8 to 12 cm, 3 to 5 in)

C--31 to 42 cm (12 to 17 in); extremely gravelly silt loam, dark grayish brown (10YR 4/2) moist; massive; soft, very friable, nonsticky, nonplastic; nonsmeary; common fine and medium roots throughout; 10 percent cobbles and 70 percent gravel by volume; slight effervescence; neutral (pH 7.3); clear broken boundary (2 to 15 cm, 1 to 6 in)

R--42 to 67 cm (17 to 26 in); bedrock

TYPE LOCATION: North Copper River Soil Survey Area, Alaska; latitude 61.60352, longitude -144.47325, UTM 6832614.03 north and UTM 634037.21 east, zone 6, Datum WGS84.

RANGE IN CHARACTERISTICS:

Soil moisture regime: udic
Soil temperature regime: cryic
Mean annual soil temperature: 0 to 5 degrees C. (32 to 41 degrees F)
Thickness of organic material: 6 to 13 cm (2 to 5 in)
Thickness of epipedon: 11 to 24 cm (4 to 9 in)
Depth to lithic contact: 25 to 56 cm (10 to 22 in)

Oi and Oe horizon:
Hue: 7.5YR or 10YR
Value: 2 to 3
Chroma: 1 to 3
Texture: Slightly decomposed organic material, moderately decomposed organic material
Organic matter: 60 to 90 percent
Reaction class: slightly acid (pH 6.1 to 6.5)

A horizon:
Hue: 7.5YR or 10YR
Value: 2 to 4
Chroma: 1 to 2
Texture: very fine sandy loam or silt loam
Sand: 22 to 60 percent
Silt: 36 to 74 percent
Clay: 4 to 8 percent
Rock fragments: 0 percent
Organic matter: 4.0 to 8.0 percent
Reaction class: slightly acid to neutral (pH 6.1 to 7.0)

Bw horizon:
Hue: 10YR or 2.5Y
Value: 3 to 5
Chroma: 2 to 4
Texture: very fine sandy loam, fine sandy loam, silt loam
Sand: 22 to 65 percent
Silt: 31 to 74 percent
Clay: 4 to 8 percent
Organic matter: 1.0 to 2.0 percent
Reaction class: slightly acid to neutral (pH 6.3 to 7.3)

C horizon:
Hue: 10YR or 2.5Y
Value: 3 to 5
Chroma: 2 to 4
Texture: Very gravelly silt loam, extremely gravelly silt loam
Sand: 23 to 37 percent
Silt: 61 to 75 percent
Clay: 2 to 6 percent
Rock fragments: 41 to 83 percent
Gravels: 36 to 72 percent
Cobbles: 5 to 11 percent
Organic matter: 0.25 to 1.0 percent
Reaction class: Neutral to slightly alkaline (pH 6.6 to 7.8)

Some pedons have a paralithic horizon above the bedrock.

COMPETING SERIES: This is the Mariaspass (MT) series.
Mariaspass has a paralithic contact and residuum parent material.

GEOGRAPHIC SETTING:
Elevation: 100 to 1200 meters (330 to 3935 ft)
Parent material: silty noncalcareous loess over gravelly colluvium
Landform: hillslopes and mountain slopes
Slopes: 5 to 30 percent
Mean annual precipitation: 300 to 1400 mm (12 to 55 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 Alterationcreek, Cirquecreek, Greylingcreek, Haggardcreek, Secondlake, and Taral series.
Alterationcreek soils have and umbric epipedon, have bedrock between 101 and 154 cm (40 and 61 in) deep, lack bedrock within 2 m (79 in), and occur on hillslopes and mountain valleys.
Cirquecreek soils have a cambic horizon, lack bedrock within 2 m (79 in), and occur on saddles and mountain slopes
Greylingcreek soils are excessively drained and occur in mountain valleys and moraines.
Haggardcreek soils are well drained, have a folistic epipedon, and occur on hillslopes and mountain slopes.
Secondlake soils are well drained, have a mollic epipedon, have bedrock between 75 and 130 cm (30 and 51 in) deep, and occur on mountain slopes landforms.
Slatka soils are somewhat poorly drained, have permafrost and cryoturbation, have a histic epipedon, lack bedrock within 2 m (79 in), and occur on mountain slopes.
Taral soils are well drained, have a mollic epipedon, lack bedrock within 2 m (79 in), and occur on mountain slopes and hillslopes.

DRAINAGE AND SATURATED HYDRAULIC CONDUCTIVITY:
Drainage class: well drained
Saturated Hydraulic Conductivity: very high in the Oi horizon, moderately high in the A, Bw, and C horizons, and moderately low in the R horizon.
Permeability: very rapid in the Oi horizon, moderate in the A, Bw, and C horizons, and slow in the R horizon.
Runoff: very high

USE AND VEGETATION:
Use: wildlife habitat, recreation, and subsistence
Native vegetation: Black spruce, bog labrador tea, feather moss

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

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: 11 to 42 cm (4 to 17 in)

Ochric epipedon: 0 to 18 cm (0 to 7 in) (Oe and A horizon)

Lithic contact: 42 to 67 cm in (17 to 26 in) (R horizon)

ADDITIONAL DATA:

User pedon Id: 2018AK261216

National Cooperative Soil Survey
U.S.A.