LOCATION SIMPSON CAEstablished Series
TAXONOMIC CLASS: Ashy, glassy, mesic Vitritorrandic Argixerolls
TYPICAL PEDON: Simpson ashy sandy loam - rangeland. (Colors are for dry soil unless otherwise stated).
A1--0 to 4 centimeters; dark grayish brown (10YR 4/2) ashy sandy loam, very dark grayish brown (10YR 3/2) moist; massive; soft, very friable, nonsticky, nonplastic; many very fine roots; many very fine interstitial pores; slightly acid (pH 6.4); abrupt smooth boundary. (2 to 13 centimeters thick).
E--4 to 9 centimeters; light brownish gray (10YR 6/2) ashy sandy loam, very dark grayish brown (10YR 3/2) moist; weak medium platy structure; soft, very friable, slightly sticky, slightly plastic; many very fine roots; many very fine interstitial and tubular pores; common clean sand grains; neutral (pH 6.6); abrupt wavy boundary. (0 to 5 centimeters thick).
Bt1--9 to 18 centimeters; dark grayish brown (10YR 4/2) ashy sandy clay loam, dark brown (10YR 3/3) moist; moderate coarse prismatic structure; hard, friable, moderately sticky, moderately plastic; common very fine and fine roots; common very fine tubular pores; many thin clay films as bridges between sand grains and in pores; common thin clay films on faces of peds; neutral (pH 6.8); clear wavy boundary. (8 to 20 centimeters thick).
Bt2--18 to 30 centimeters; brown (10YR 4/3) ashy clay, dark brown (10YR 3/3) moist; strong medium and coarse prismatic structure; very hard, firm, very sticky, very plastic; many very fine roots between peds and few very fine and fine roots throughout; common very fine tubular pores; many thin, and few moderately thick dark brown (10YR 3/3) clay films on faces of peds and in pores; neutral (pH 6.8); gradual smooth boundary. (10 to 23 centimeters thick).
Bt3--30 to 43 centimeters; brown (10YR 4/3) ashy clay, dark brown (10YR 3/3) moist; moderate coarse prismatic structure; very hard, firm, very sticky, very plastic; many very fine roots between peds, and few very fine and medium roots throughout; common very fine tubular pores; many thin and few moderately thick dark brown (10YR 3/3) clay films on faces of peds and in pores; neutral (pH 7.0); clear wavy boundary. (10 to 25 centimeters thick).
Bt4--43 to 58 centimeters; brown (10YR 4/3) ashy sandy clay loam, dark brown (10YR 3/3) moist; moderate medium and coarse prismatic structure; hard, friable, moderately sticky, moderately plastic; few very fine, fine, and medium roots; few very fine interstitial, and common very fine tubular pores; common thin dark brown (10YR 3/3) clay films on faces of peds and in pores; neutral (pH 7.0); clear wavy boundary. (8 to 36 centimeters thick).
C1--58 to 79 centimeters; brown (10YR 4/3) ashy sandy loam, dark brown (10YR 3/3) moist; massive; slightly hard, very friable, nonsticky, nonplastic; few very fine and fine roots; common very fine, and few fine tubular pores; neutral (pH 7.0); clear wavy boundary. (13 to 38 centimeters thick).
C2--79 to 94 centimeters; pale brown (10YR 6/3) gravelly ashy loamy sand, dark brown (10YR 3/3) moist; massive; slightly hard, very friable, nonsticky, nonplastic; few very fine and fine roots; few very fine tubular, and many very fine interstitial pores; 25 percent gravel; slightly alkaline (pH 7.4); clear wavy boundary. (13 to 25 centimeters thick).
2Ck--94 to 122 centimeters; very dark gray (10YR 3/1) and dark gray (10YR 4/1) and gray (10YR 5/1) extremely gravelly ashy sand, very dark gray (10YR 3/1) and dark gray (10YR 4/1) moist; single grain; loose, nonsticky, nonplastic; common very fine and fine roots; many very fine and fine, and few medium interstitial pores; 60 percent gravel; common 0.1 to 1 millimeter thick, very pale brown (10YR 8/2) lime coatings on bottom of rock fragments; moderately alkaline (pH 8.0).
TYPE LOCATION: Modoc County, California; about 1.8 miles north of the center of Cedarville, and about 550 feet south and 2650 feet east of the northwest corner of sec. 32, T. 43 N., R. 16 E., Mount Diablo base line and meridian; 41 degrees, 33 minutes, 26.0 seconds north latitude and 120 degrees, 10 minutes, 18.9 seconds west longitude, NAD 1927; Cedarville quadrangle.
RANGE IN CHARACTERISTICS:
Soil moisture - Usually dry, dry during summer and fall months in most years, moist in winter and spring. Soil moisture regime is aridic bordering xeric.
Soil temperature - Mean annual soil temperature ranges from 47 to 53 degrees F.
Mollic epipedon thickness - 50 to 79 centimeters (20 to 31inches), includes most or all of the argillic horizon.
Solum thickness - 53 to 69 centimeters (21 to 27 inches).
Depth to the unconformable 2C horizons - 61 to 97 centimeters (24 to 38 inches).
Volcanic glass content: 30 to 60 percent volcanic glass and glass aggregates in the coarse silt to fine sand fraction.
A horizon
Values: 4 or 5 dry and 2 or 3 moist.
Chroma: 2 or 3.
Structure: Massive or weak or moderate, very thin to medium platy.
Consistence: Soft or slightly hard when dry.
Organic matter: 1 to 2 percent.
Reaction: Slightly acid to slightly alkaline.
Carbonates: Noneffervescent.
E horizon (when present)
Value: 6 or 7 dry and 3 or 4 moist.
Chroma: 1 or 2 dry; 2 moist.
Structure: Weak thin or medium platy; weak or moderate, very fine or fine granular; or weak or moderate, very fine or fine subangular blocky.
Reaction: Slightly acid to slightly alkaline.
Carbonates: Noneffervescent.
Other features: In some areas the E horizon is lacking and only occurs as a scattering of bleached sand grains on prism tops.
Bt horizon
Hue: 10YR or 7.5YR.
Value: 4 to 6 dry and 3 or 4 moist.
Chroma: 2 or 3.
Texture: Ashy clay loam, ashy clay, ashy sandy clay loam or ashy sandy clay.
Clay content: Averages 35 to 50 percent.
Structure: Strong to weak, fine to coarse prismatic or subangular blocky.
Organic matter: 0.5 to 2 percent.
Reaction: Neutral.
Carbonates: Noneffervescent.
C horizon (when present)
Value: 4 to 6 dry and 3 or 4 moist.
Chroma: 2 or 3.
Texture: Stratified ashy sandy loam, ashy fine sandy loam, ashy loam, or ashy loamy sand; averages gravelly ashy sandy loam.
Rock fragments: Averages 10 to 30 percent, mainly gravel.
Clay content: Averages 5 to 10 percent.
Organic matter: 0.5 to 1 percent.
Reaction: Neutral to slightly alkaline.
Carbonates: Noneffervescent.
2Ck or 2C horizon
Color is dependent upon the color of the individual gravel and sand grains.
Value: 3 to 7 dry and 2 to 5 moist.
Chroma: 1 to 3.
Texture: Stratified gravel to ashy sand; averages very gravelly ashy sand or extremely gravelly ashy sand.
Rock fragments: Averages 50 to 80 percent, mainly gravel.
Clay content: 0 to 5 percent.
Organic matter: 0 to 0.5 percent.
Reaction: Slightly alkaline or moderately alkaline.
Carbonates: Noneffervescent to strongly effervescent.
COMPETING SERIES: These are the Ashone (NV), Bidwell, Coppersmith (CA) and Ponyspring (NV) series. Ashone soils are moderately deep to paralithic contacts. Bidwell soils have a mollic epipedon 25 to 41 cm (10 to 16 inches) thick. Coppersmith soils have 20 to 41 centimeter (8 to 16 inch) thick mollic epipedons and 18 to 27 percent clay in the control section. Ponyspring soils have 25 to 36 centimeter (10 to 14 inch) thick mollic epipedons and 18 to 27 percent clay in the control section.
GEOGRAPHIC SETTING: Simpson soils are on fan remnants. Slopes range from 0 to 15 percent. These soils formed in volcanic ashand alluvium superimposed over very gravelly ashy sandy lacustrine material, both of which were derived mainly from tuffs, basalts and andesites. Elevations range from 1,280 to 1,542 meters (4,200 to 5,060 feet). The climate is cool, continental with mean annual precipitation of 305 to 406 millimeters (12 to 16 inches), most of which comes in the form of snow. The mean annual air temperature ranges from 7.5 to 11.0 degrees C. (46 to 52 degrees F.); frost-free period is 90 to 120 days.
GEOGRAPHICALLY ASSOCIATED SOILS: These are the Bidwell, Buntingville, Donica and Surprise soils. Bidwell soils have 18 to 35 percent clay and do not have 2C horizons with 50 to 80 percent rock fragments. Buntingville soils are somewhat poorly drained, and have 20 to 35 percent clay and do not have 2C horizons with 50 to 80 percent rock fragments. Donica soils have ashy-skeletal control sections. Surprise soils do not have argillic horizons.
DRAINAGE AND PERMEABILITY: Well drained; surface runoff is slow; permeability is slow; saturated hydraulic conductivity class is moderately low.
USE AND VEGETATION: Areas of these soils are used for production of dryland small grains and pasture, and irrigated alfalfa in rotation with small grains and pasture. They are also used for livestock grazing and wildlife habitat. The native vegetation consists mainly of big sagebrush, antelope bitterbrush and bluebunch wheatgrass, and scattered juniper.
DISTRIBUTION AND EXTENT: These soils occur in northeastern California. These soils are of limited extent. MLRA 23.
MLRA SOIL SURVEY REGIONAL OFFICE (MO) RESPONSIBLE: Davis, California.
SERIES ESTABLISHED: Surprise Valley-Home Camp Area, Modoc and Lassen Counties, California, and Washoe County, Nevada, 1957. Simpson was derived from Simpson Creek in Surprise Valley, California.
REMARKS: These soils were formerly classified as Chestnut soils.
The series is reclassified in 2006 based on the optical grain count of associated soils. It was previously classified as Fine, smectitic, mesic Pachic Argixerolls.
Diagnostic horizons and features recognized in this pedon are:
Mollic epipedon - The zone from the surface to 58 centimeters (23 inches) (A, E, Bt1, Bt2, Bt3, Bt4 horizons).
Argillic horizon - The zone from 9 to 58 centimeters (Bt1, Bt2, Bt3, Bt4 horizons).
Vitritorrandic feature - The horizons within 75 centimeters of the surface with 30 to 60 percent volcanic glass in the coarse silt to sand fractions.
Particle-size control section - The zone from 9 to 58 centimeters (Bt1, Bt2, Bt3, Bt4 horizons).