LOCATION MODOC CA+OR UTEstablished Series
TAXONOMIC CLASS: Fine-loamy, mixed, superactive, mesic Vitritorrandic Durixerolls
TYPICAL PEDON: Modoc ashy loam--on a southwest-facing slope of 2 percent under big sagebrush, basin wildrye, Nevada bluegrass, and cheatgrass at 4,235 feet elevation--rangeland. (Colors are for dry soil unless otherwise noted. When described on August 19, 1980, the soil was dry throughout.)
A1--0 to 3 inches; grayish brown (10YR 5/2) ashy loam, very dark grayish brown (10YR 3/2) moist; moderate medium granular structure; slightly hard, friable, slightly sticky and slightly plastic; many very fine and fine roots; common very fine interstitial and tubular pores; neutral (pH 7.0); clear smooth boundary. (2 to 5 inches thick).
A2--3 to 12 inches; grayish brown (10YR 5/2) ashy loam, very dark grayish brown (10YR 3/2) moist; moderate medium subangular blocky structure; slightly hard, friable, slightly sticky and slightly plastic; many very fine and fine, few medium and coarse roots; common very fine interstitial and tubular pores; neutral (pH 7.3); clear smooth boundary. (7 to 11 inches thick).
BA--12 to 21 inches; light brownish gray (10YR 6/2) loam, dark grayish brown (10YR 4/2) moist; moderate medium subangular blocky structure; slightly hard, friable, slightly sticky and slightly plastic; common very fine and fine, few medium roots; common very fine and fine interstitial and tubular pores; slightly alkaline (pH 7.8); clear smooth boundary. (0 to 9 inches thick).
Bt--21 to 34 inches; pale brown (10YR 6/3) sandy clay loam, brown (10YR 4/3) moist; moderate fine and medium angular blocky structure; hard, firm, moderately sticky and moderately plastic; few very fine and fine roots; few very fine and fine interstitial and tubular pores; few distinct and many faint clay films on faces of peds and lining pores; moderately alkaline (pH 8.0); abrupt wavy boundary. (6 to 17 inches thick).
Bqkm1--34 to 42 inches; light gray (10YR 7/2) cemented material, brown (10YR 5/3) moist; moderate medium thick and very thick platy structure; some plates have a thin continuous opal laminar cap; very hard, very firm and brittle; strongly cemented by opaline silica; roots are horizontal and matted on top of this horizon; few very fine tubular pores; slightly effervescent; moderately alkaline (pH 8.0); clear wavy boundary. (3 to 10 inches thick).
Bqkm2--42 to 55 inches; light gray (10YR 7/2) cemented material, brown (10YR 5/3) moist; strong very thick platy structure; some plates have thin opal laminar caps; extremely hard, very firm and brittle; strongly cemented by opaline silica; few very fine tubular pores; strongly effervescent; accumulations of lime in seams and thin layers of lime coat top of plates; moderately alkaline (pH 8.0); clear wavy boundary. (2 to 15 inches thick).
2C--55 to 60 inches; light gray (10YR 7/2) sandy loam, brown (10YR 5/3) moist; massive; soft, very friable, nonsticky and nonplastic; common very fine interstitial pores; moderately alkaline (pH 8.0).
TYPE LOCATION: Siskiyou County, California; in Butte Valley about 3.5 miles south-southwest of Dorris and west of U.S. Highway 97; about 350 feet south and 2,050 feet west of the northeast corner of section 14, T. 47 N., R. 1 W.; USGS Dorris 7.5 minute topographic quadrangle; 41 degrees 55 minutes 22 seconds north latitude and 121 degrees 56 minutes 46 seconds west longitude, NAD27.
RANGE IN CHARACTERISTICS:
Soil moisture - The soil temperature at a depth of 20 inches is above 41 degrees F. from about March 15 to December 1 (255 days) and is above 47 degrees F. from about April 15 to November 15 (210 days); The soil between depths of 6 to 16 inches is dry in all parts from mid-June to mid-November (about 120 to 140 days); Aridic moisture regime that borders on xeric.
Mean annual soil temperature - 47 to 53 degrees F.
Mollic epipedon thickness - 10 to 14 inches; includes the upper part of the Bt horizon in some pedons.
Depth to duripan - 20 to 40 inches.
Depth to bedrock - Greater than 60 inches; Some pedons have paralithic contacts within 60 inches of the soil surface.
Salinity (EC): 0 to 2 mmhos/cm.
Sodicity (SAR): 0 to 4.
A horizons - Dry color: 10YR 5/3, 5/2, 4/2 and 4/3.
Moist color: 10YR 3/3, 3/2 or 2/2.
Reaction: Slightly acid through slightly alkaline.
Texture: Ashy sandy loam, ashy fine sandy loam, ashy loam, gravelly ashy sandy loam, gravelly ashy fine sandy loam or gravelly ashy loam.
Clay content: 10 to 25 percent.
Rock fragments: 0 to 20 percent gravel.
Volcanic glass content: 20 to 40 percent in coarse silt through fine sand fractions.
Oxalate Al + 1/2 oxalate iron: 0.15 to 0.40 percent.
Bt horizon - Dry color: 10YR 6/4, 6/3, 6/2, 5/4, 5/3, 4/4, 4/3, 7.5YR 5/4, 4/4, 5YR 5/4, 4/4; 2.5Y 5/3 or 4/4.
Moist color: 10YR 4/4, 4/3, 4/2, 3/4, 3/3; 7/5YR 4/4, 3/4; 5YR 4/4, 4/3 or 2.5Y 4/4.
Texture: Loam, sandy clay loam, clay loam, gravelly sandy clay loam, or gravelly clay loam.
Clay content: 25 to 35 percent.
Rock fragments: 0 to 30 percent gravel.
Reaction: Neutral through moderately alkaline.
Other features: This horizon has 5 to 15 more clay than the A horizons.
Bqkm horizons - Cementation: Indurated or strongly cemented and indurated in some part or has thin continuous opal capping on plates.
Structure: Massive or platy.
Rupture resistance: Extremely hard or very hard when dry and extremely or very firm when moist.
Other features: In some pedons the lower part of the duripan is weakly cemented and contains up to 25 percent gravel; Thin seams of lime or lime-silica occur in some places of the Bqk horizon. Thickness ranges from 5 to 25 inches.
COMPETING SERIES: These are the Homehollow (T) and St. Andrews series.
Homehollow soils have lithic contacts below the duripan. St. Andrews soils have dense glacial till below the duripan.
GEOGRAPHIC SETTING: Modoc soils are on lake terraces and fan remnants. These soils formed in volcanic ash over lacustrine deposits or alluvium derived from basalt, andesite, and pyroclastic rocks. Slopes are 0 to 15 percent. Elevations are 3,700 to 5,000 feet. The climate is semiarid with cool, moist winters and warm, dry summers. The mean annual precipitation is 9 to 16 inches. Annual snowfall is 20 to 30 inches. The mean annual temperature is 45 to 52 degrees F. The average January temperature is 27 to 29 degrees F. and the average July temperature is 65 to 68 degrees F. The frost-free period is 50 to 130 days.
GEOGRAPHICALLY ASSOCIATED SOILS: These are the Inlow, Munnell, Ocho, Poman, and Rojo soils. Inlow soils have natric horizons. Munnell soils do not have duripans. Ocho soils have natric horizons and are less than 20 inches deep to a duripan. Poman soils are sandy. Rojo soils are coarse-loamy.
DRAINAGE AND PERMEABILITY: Well drained; medium surface runoff; moderately slow permeability.
USE AND VEGETATION: Modoc soils are used for cropland, hay and pasture, and as rangeland. Natural vegetation is big sagebrush, rabbitbrush, antelope bitterbrush, bluebunch wheatgrass, Idaho fescue, needlegrass, and basin wildrye.
DISTRIBUTION AND EXTENT: Northeastern California, south-central Oregon, and western Utah. These soils are moderately extensive. The series concept and main acreage is in MLRA 21, while other acreage occurs in MLRA 10 in Oregon and 28A in Utah.
MLRA SOIL SURVEY REGIONAL OFFICE (MO) RESPONSIBLE: Davis, California.
SERIES ESTABLISHED: Lassen and Modoc Counties (Big Valley Area), California, 1920. The current series type location was moved to Siskiyou County (Butte Valley-Tule Lake Soil Survey Area) in 1985. This was done to more accurately reflect the mapping done in Modoc and Siskiyou counties.
REMARKS: This revision of August 2004 updates the taxonomic class from Fine-loamy, mixed, superactive, mesic Argiduridic Durixerolls based on laboratory data and the series concept centered in volcanic ash influenced areas of MLRA 21. Modoc components in MLRA 28A need correlation to another series.
Diagnostic horizons and features recognized in this pedon are:
Mollic epipedon - The zone from the soil surface to 12 inches (A1 and A2 horizons).
Vitrandic intergrade feature - The zone from the soil surface to 12 inches (A1 and A2 horizons).
Argillic Horizon - The zone from 21 to 34 inches (Bt horizon).
Duripan - The zone from 34 to 55 inches (Bqkm1 and Bqkm2 horizons).
Particle-size control section - The zone from 21 to 34 inches (Bt horizon).
The superactive cation exchange activity class was added in 03/2003 to the taxonomic classification by the National Soil Survey Center on request of the Reno MLRA office, without review of the soil series property data.
ADDITIONAL DATA: The typical pedon at the series type location has full characterization data by the Soil Survey Laboratory (SSL), Lincoln, NE, as soil survey sample number S80CA-093-015 (pedon # 80P0458). The control section is 27.9 percent clay. This soil probably did not disperse well because 2.5 X 17.1 (15 bar water) = 42.75.