LOCATION TWINHILLS AK
Established Series
SAS/TJR/MPR
02/2022
TWINHILLS SERIES
Landscape--hills
Landform--hillslopes
Slope--25 to 70 percent
Parent material--colluvium influenced by volcanic ash over residuum derived from sedimentary or volcanic rock
Mean annual precipitation--about 900 mm
Mean annual air temperature--about 1 degrees C
Depth class--moderately deep
Drainage class--well drained
Soil moisture regime--udic
Soil temperature regime--cryic
Soil moisture subclass--typic
TAXONOMIC CLASS: Medial-skeletal, amorphic, shallow Folistic Haplocryands
TYPICAL PEDON: Twin hills very gravelly medial silt loam on an east-facing, linear backslope of a hill, on a slope of 65 percent at an elevation of 97 m (The soil was moist throughout when described on July 24, 2013.)
Oe--0 to 7 cm; moderately decomposed plant material; many very fine to medium and common coarse roots; extremely acid (pH 3.8) clear smooth boundary
Oa--7 to 20 cm; highly decomposed plant material; common very fine to coarse roots; very strongly acid (pH 4.7) clear smooth boundary
A/B--20 to 45 cm; very gravelly medial silt loam, matrix color 60 percent brown (7.5YR 4/2) dry, very dark brown (7.5YR 2.5/2) moist, and 40 percent brown (10YR 5/3) dry, dark brown (10YR 3/3) moist; moderate medium granular structure; slightly hard, friable, nonsticky and slightly plastic; common very fine to medium roots; 35 percent gravel and 5 percent cobbles; extremely acid (pH 4.1) clear smooth boundary
Bw--45 to 60 cm; very gravelly medial silt loam, matrix color 70 percent brown (10YR 5/3) dry, dark brown (10YR 3/3) moist, and 30 percent yellowish brown (10YR 5/4) dry, dark yellowish brown (10YR 3/4) moist; weak fine subangular blocky structure; slightly hard, friable, slightly sticky and slightly plastic; common very fine and fine roots; 45 percent gravel and 5 percent cobbles; extremely acid (pH 3.6) clear smooth boundary
2Cr--60 to 130 cm; paralithic bedrock; irregular very abrupt boundary
2R--130 cm; bedrock
TYPE LOCATION: Dillingham Census Area, Alaska, about 6 km north of the village of Togiak; latitude 59.1124307 degrees north, longitude 160.3839473 degrees west, datum WGS 84 (coordinates determined with a GPS)
RANGE IN CHARACTERISTICS:
Mean annual soil temperature--0.6 to 2.2 degrees C
Soil moisture control section--dry less than 45 consecutive days in June through October (udic moisture regime)
Lithology of rock fragments--sedimentary, volcanic
Depth to paralithic contact--50 to 80 cm (moderately deep)
Layers influenced by volcanic ash
*Thickness--50 to 80 cm
*Phosphorous retention--85 to 100 percent
*Bulk density--0.45 to 0.9 g/cm3
*Ammonium oxalate Al plus 1/2 Fe--2 to 4 percent
*Volcanic glass content--10 to 40 percent
*Ammonium oxalate Si-0.5 to 1.0 percent
*Ammonium oxalate Fe--0.5 to 2.1 percent
Particle-size control section
*Clay content--3 to 16 percent
*Sand content--20 to 65 percent
*Total rock fragment content--35 to 55 percent
Oe horizon
Thickness--5 to 15 cm
Oa horizon
Thickness--5 to 15cm
A or A/B horizon
Hue--5YR, 7.5YR, 10YR
Value--2 or 3 moist, 4 to 6 dry
Chroma--1 to 3 moist
Fine-earth texture--medial silt loam, medial sandy loam, medial fine sandy loam
Clay content--3 to 16 percent
Reaction--4.0 to 5.5
Total rock fragment content--15 to 40 percent
Gravel content--0 to 35 percent
Cobble content--0 to 5 percent
Thickness--10 to 25 cm
Bulk density--0.5 to 0.9 g/cm3
Phosphorous retention--85 to 100 percent
Volcanic glass content--10 to 40 percent
Bw horizon
Hue--7.5YR, 10YR
Value--3 or 4 moist, 5 or 6 dry
Chroma--3 or 4 moist
Fine-earth texture--medial silt loam, medial loam
Clay content--3 to 16 percent
Reaction--3.5 to 5.5
Total rock fragment content--35 to 55 percent
Gravel content--35 to 45 percent
Cobble content--0 to 20 percent
Thickness--5 to 60 cm
Bulk density--0.7 to 0.9 g/cm3
Phosphorous retention--85 to 100 percent
Volcanic glass content--10 to 40 percent
2Cr horizon
Thickness--25 to 80 cm
COMPETING SERIES: None
GEOGRAPHIC SETTING:
Elevation--50 to 500 m
Climate--warm, moist summers; cold, moist winters
Mean annual precipitation--640 to 1900 mm
Mean annual air temperature-- -1.9 to 1.8 degrees C
Frost-free period--80 to 140 days
GEOGRAPHICALLY ASSOCIATED SOILS:
Mitlak--aquic conditions below a depth of 50 cm; andic soil properties; plains and lower mountain slopes
Klak--more than 150 cm (very deep) to lithic bedrock; lower mountain slopes
Nagugun--more than 150 cm (very deep) to lithic bedrock; glaciated plains
Kashaiak--less than 50 cm (shallow) to lithic bedrock; no andic soil properties; upper third of mountain slopes
DRAINAGE AND SATURATED HYDRAULIC CONDUCTIVITY:
Drainage class--well drained
Saturated hydraulic conductivity (Ksat)--high throughout A and B horizons
USE AND VEGETATION:
Use--wildlife habitat, recreation, subsistence
Potential natural vegetation--alder, bluejoint, arctic starflower, spreading woodfern, common ladyfern
DISTRIBUTION AND EXTENT: Ahklun Mountains, Alaska; MLRA 237; moderate extent
SOIL SURVEY REGIONAL OFFICE (SSRO) RESPONSIBLE: WASILLA, ALASKA
SERIES ESTABLISHED: Togiak National Wildlife Refuge, Dillingham Census Area, Alaska; 2019
REMARKS:
Diagnostic horizons and other features in this pedon
*Particle-size control section--zone from 20 to 60 cm
*Folistic epipedon--Oe and Oa horizons
*Andic soil properties--zone from 20 to 60 cm
*Cambic horizon--zone from 45 to 60 cm
*Depth to paralithic contact--60 cm
*Depth to lithic contact--130 cm
See laboratory pedon number 13N0047, layer 13N00122, for a Bw horizon that has andic soil properties and amorphic mineralogy.
National Cooperative Soil Survey
U.S.A.