LOCATION ATWELL CA
Established Series
Rev: JAD/JPS/ET
07/2016
ATWELL SERIES
The Atwell series consists of very deep, moderately well drained soils formed in material from sheared sedimentary rocks. Atwell soils are on mountains and have slopes of 15 to 50 percent. The mean annual precipitation is about 2030 millimeters (80 inches) and the mean annual temperature is about 12 degrees C (54 degrees F).
TAXONOMIC CLASS: Fine, mixed, active, isomesic Oxyaquic Hapludalfs
TYPICAL PEDON: Atwell silt loam - on a southwest-facing slope of 30 percent under redwood, Douglas-fir, tanoak, western hemlock, grand fir, rhododendron, huckleberry, Oregon grape, salal, swordfern, deer fern, and oxalis, at 699 feet (213 meters) elevation. In an area of Atwell-Ladybird complex, 30 to 50 percent slopes. (Colors are for moist soil unless otherwise stated. When described on April 13, 1981, the soil was moist to a depth of 76 centimeters and wet from 76 to 205 centimeters.)
Oi -- 0 to 5 centimeters (0 to 2 inches); slightly decomposed needles, leaves and twigs; moderately acid (pH 6.0); clear wavy boundary
A -- 5 to 17 centimeters (2 to 7 inches); dark brown (10YR 3/3) silt loam, grayish brown (10YR 5/2) dry; moderate medium granular and moderate very fine subangular blocky structure; hard, firm, slightly sticky, slightly plastic; many very fine and fine, and common medium roots; many fine irregular pores; about 10 percent gravel; slightly acid (pH 6.5); clear wavy boundary.
AB -- 17 to 29 centimeters (7 to 11 inches); brown (10YR 4/3) clay loam, brown (10YR 5/3) dry; moderate medium subangular blocky structure; hard, firm, moderately sticky, slightly plastic; common very fine, fine and medium, and few coarse roots; common very fine tubular, and common fine irregular pores; about 10 percent gravel; moderately acid (pH 6.0); clear wavy boundary.
BAt -- 29 to 59 centimeters (11 to 23 inches); dark yellowish brown (10YR 4/4) clay loam, yellowish brown (10YR 5/4) dry; moderate coarse subangular blocky, parting to moderate medium subangular blocky structure; hard, firm, moderately sticky, moderately plastic; common very fine, fine and coarse, and many medium roots; few fine irregular, and common very fine, fine and medium tubular pores; common faint clay films on faces of peds; about 10 percent gravel; moderately acid (pH 6.0); clear irregular boundary.
Bt -- 59 to 81 centimeters (23 to 32 inches); light olive brown (2.5Y 5/4) gravelly clay loam, pale yellow (2.5Y 7/4) dry; moderate medium subangular blocky structure; hard, firm, moderately sticky, very plastic; common very fine and fine roots; few very fine and fine tubular pores; few distinct clay films on faces of peds; about 30 percent gravel; moderately acid (pH 6.0); clear wavy boundary.
2Cg1 -- 81 to 103 centimeters (32 to 41 inches); greenish gray (5GY 5/1) clay, light gray (N 7/) dry; massive; very hard, very firm, moderately sticky, very plastic; few very fine and fine roots; few very fine and fine tubular pores; many medium prominent reddish yellow (7.5YR 6/6) masses of iron accumulations, strong brown (7.5YR 5/6) moist; about 10 percent gravel; moderately acid (pH 6.0); clear smooth boundary.
2Cg2 -- 103 to 155 centimeters (41 to 61 inches); dark bluish gray (5B 4/1) clay, gray (N 6/) dry; massive; very hard, very firm, moderately sticky, very plastic; few very fine and fine roots; few very fine and fine tubular pores; common fine prominent yellowish brown (10YR 5/4) masses of iron accumulations, brownish yellow (10YR 6/6) dry; about 10 percent gravel; slightly acid (pH 6.5); diffuse smooth boundary.
2Cg3 -- 155 to 205 centimeters (61 to 81 inches); black (5Y 2.5/1) clay, gray (N 5/) dry; massive; very hard, very firm, moderately sticky, very plastic; few very fine and fine roots; few very fine and fine tubular pores; common prominent yellowish brown (10YR 5/4) masses of iron accumulations, brownish yellow (10YR 6/6) dry; about 10 percent gravel; many slickensides; slightly acid (pH 6.5).
TYPE LOCATION: Redwood National Park, Humboldt County, California; located approximately 61 meters north of Miller Creek, 49 meters west of C-40 road; Bald Hills Quadrangle; WGS84 Decimal degrees 41.2310361 latitude and -123.9972806 longitude, UTM Zone 10 416420mE 4564884mN; NAD83.
RANGE IN CHARACTERISTICS:
Soil moisture: The soil moisture control section is continuously moist in all parts in most years. The soils have an udic moisture regime and an oxyaquic regime subgroup. A seasonal water table is present for 20 or more consecutive days or 30 or more cumulative days in most years within the zone from 70 to 100 centimeters (28 to 39 inches).
Soil temperature: The mean annual soil temperature is 10 to 13 degrees C (50 to 55 degrees F). The difference between mean summer and mean winter temperature is 2 to 4 degrees C.
Depth to redoximorphic features: 70 to 100 centimeters.
Particle-Size Control Section (weighted average):
Rock fragments: 5 to 35 percent gravel.
Clay content: 35 to 50 percent.
O horizon
Hue: 10YR.
Value: 2 through 6 dry and moist.
Chroma: 1 through 4 dry and moist.
Texture: slightly decomposed organic material.
Wood fragments: 0 to 35 percent.
Clay content: 0 to 5 percent.
Reaction: moderately to very strongly acid.
A horizon
Hue: 10YR.
Value: 5 or 6 dry, 3 or 4 moist.
Chroma: 2 or 3 dry, 2 or 3 moist.
Texture of fine earth: clay loam, silt loam or silty clay loam.
Rock fragments: 2 to 25 percent.
Clay content: 23 to 35 percent.
Reaction: slightly or moderately acid.
Bt horizon
Hue: 10YR or 2.5Y.
Value: 6 or 7 dry, 4 or 5 moist.
Chroma: 3 or 4 dry, 3 or 4 moist.
Texture of fine earth: clay loam or clay.
Rock fragments: 3 to 35 percent gravel.
Clay content: 35 to 50 percent.
Reaction: moderately to strongly acid.
Redoximorphic features:
Hue: 10YR.
Value: 6 dry, 5 moist.
Chroma: 6 dry, 6 moist.
2Cg horizon
Hue: 5Y, 2.5Y, N 5/, 6/, 7/, 5GY or 5B.
Value: 6 or 7 dry, 2 through 6 moist.
Chroma: / through 2 dry, / through 2 moist.
Texture of fine earth: clay or silty clay.
Rock fragments: 5 to 35 percent.
Clay content: 35 to 60 percent.
Reaction: moderately acid to moderately alkaline.
Redoximorphic features:
Hue: 7.5YR or 10YR.
Value: 6 dry, 5 moist.
Chroma: 6 dry, 4 through 6 moist.
Slickensides are common in some profiles.
COMPETING SERIES: At this time there no other series in this family.
GEOGRAPHIC SETTING: Atwell soils are on mountains. They occupy concave to irregular, unstable slopes in areas of high drainage density. Slips and slides are common. Seeps and springs are common. Slopes are 15 to 50 percent. Elevations are 18 to 874 meters (60 to 2870 feet). These soils formed in earthflow colluvium from sheared sandstone and mudstone. The climate is humid with cool, foggy summers and cool, rainy winters. Mean annual precipitation is 1780 to 2290 millimeters (70 to 90 inches). Mean January temperature is about 9 degrees C; mean July temperature is about 14 degrees C; and the mean annual temperature is 10 to 13 degrees C (50 to 55 degrees F). Frost-free season is about 250 to 290 days.
GEOGRAPHICALLY ASSOCIATED SOILS: These are the
Coppercreek and
Ladybird soils. Coppercreek and Ladybird soils are fine-loamy and lack redoximorphic features within 150 centimeters of the soil surface. The Coppercreek and Ladybird soils are on drier slopes above the Atwell soils.
DRAINAGE AND SATURATED HYDRAULIC CONDUCTIVITY: Moderately well drained; very high runoff; moderately high saturated hydraulic conductivity in the A horizon, low to very low in the 2Cg horizon. Subsoils are continuously moist.
USE AND VEGETATION: This soil has been used for commercial timber, wildlife, and watershed. Natural vegetation consists of redwood, Douglas-fir, grand fir, western red cedar, California laurel, tanoak, bigleaf maple, huckleberry, salal, and swordfern.
DISTRIBUTION AND EXTENT: Coastal Redwood Belt; MLRA 4b. The series is not extensive.
MLRA SOIL SURVEY REGIONAL OFFICE (MO) RESPONSIBLE: Davis, California.
SERIES ESTABLISHED: Humboldt County, California, 2013. Proposed 1957. Source of name is Atwell Creek, located south of the town of Rio Dell.
REMARKS: Diagnostic horizons and features recognized in this pedon are:
1. Ochric epipedon - the zone from 0 to 29 centimeters (A & AB horizons)
2. Argillic horizon - the zone from 29 to 81 centimeters (BAt & Bt horizons)
3. Redoximorphic features - in the zone from 81 to 205 centimeters (2Cg1, 2Cg2 & 2Cg3 horizons)
4. Hapludalfs feature -. Base saturation of 35 to 50 percent, by ammonium acetate, within the zone from 29 and 81 centimeters (Bat & Bt horizons)
5. Oxyaquic Hapludalfs - seasonal water table, reduced matrix, and aquic conditions for more than 30 days in most years within the zone from 81 to 100 centimeters
6. Particle-size control section - the zone from 29 to 79 centimeters, averages 35 percent clay, by field estimate, and 25 percent rock fragments, by volume. CEC/clay ratio averages 0.50
Typical pedon location was changed to better reflect the geographic distribution of the Atwell series (August 2007).
ADDITIONAL DATA: California Soil-Vegetation Survey samples 56-CA-12-14X and 57-CA-12-11X were collected at the type location. California Soil- Vegetation Survey sample 82-CA-12-03X was collected from this pedon in Redwood National Park. California Soil-Vegetation Survey sample 62-CA-12-28X was collected from another Atwell pedon in Humboldt County.
NASIS User Pedon ID: 81CA605REDW003
Soil classified using the 12th Edition of the Keys to Soil Taxonomy.
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National Cooperative Soil Survey
U.S.A.