LOCATION DIAZ CA+NV OREstablished Series
TAXONOMIC CLASS: Fine, smectitic, mesic Xeric Haplargids
TYPICAL PEDON: Diaz very cobbly silt loam--on a 3 percent south-facing slope under Wyoming big sagebrush, rabbitbrush, horsebrush, and cheatgrass at 4,620 feet elevation--rangeland. (Colors are for dry soil unless otherwise noted. When re-described on November 11, 1979, the soil was moist to about 8 inches and dry below.)
A--0 to 3 inches; light brownish gray (10YR 6/2) very cobbly silt loam, dark grayish brown (10YR 4/2) moist; moderate medium platy structure; slightly hard, friable, slightly sticky and slightly plastic; few very fine roots; many very fine interstitial pores; 20 percent cobbles and 20 percent gravel; slightly alkaline (pH 7.5); abrupt smooth boundary. (2 to 5 inches thick)
BAt--3 to 7 inches; brown (7.5YR 5/2) silty clay loam, brown (7.5YR 4/2) moist; moderate medium subangular blocky structure parting to strong very fine granular; slightly hard, friable, moderately sticky and moderately plastic; common very fine and fine roots; many very fine interstitial pores; few faint films on faces of peds and lining pores; slightly alkaline (pH 7.5); clear smooth boundary. (2 to 4 inches thick)
Bt1--7 to 16 inches; pinkish gray (7.5YR 6/2) silty clay, brown (7.5YR 4/2) moist; moderate coarse prismatic structure parting to moderate medium subangular blocky; very hard, firm, moderately sticky and moderately plastic; common fine and medium roots; many very fine tubular pores; many faint clay films on faces of peds and lining pores; many pressure faces; slightly effervescent; moderately alkaline (pH 8.0); clear smooth boundary.
Bt2--16 to 21 inches; light brown (7.5YR 6/4) silty clay, brown (7.5YR 4/4) moist; weak fine and medium prismatic structure parting to moderate medium and coarse angular blocky; very hard, firm, very sticky and very plastic; common fine and medium roots; many very fine tubular pores; common faint and distinct clay films on faces of peds and lining pores; slightly effervescent; moderately alkaline (pH 8.0); clear smooth boundary.
Bt3--21 to 25 inches; brown (7.5YR 5/4) silty clay, brown (7.5YR 4/4) moist; weak fine and medium prismatic structure parting to moderate medium and coarse angular blocky; very hard, firm, very sticky and very plastic; common very fine roots; common very fine tubular pores; common faint and distinct clay films on faces of peds and lining pores; strongly effervescent; moderately alkaline (pH 8.2); clear wavy boundary. (Combined thickness of the Bt horizons is 18 to 36 inches.)
R--25 inches; hard platy basalt; upper 3 inches are slightly weathered and with some horizontal fractures; many discontinuous coats of opaline silica and secondary carbonates; clay films coat some horizontal fractures.
TYPE LOCATION: Lassen County, California; in Secret Valley about 1.3 miles east of U.S. Highway 395; found by going east on a dirt road directly across from the intersection of Highway 395 and the Karlo Road, then about 330 feet north of the dirt road, and about 100 feet west of a north-south trending dirt road; approximately 2,000 feet west and 1,350 feet north of the southeast corner of section 36, T. 32 N., R. 15 E.; USGS Five Springs 7.5 minute topographic quadrangle; 40 degrees 35 minutes 19 seconds north latitude and 120 degrees 13 minutes 29 seconds west longitude, NAD27.
RANGE IN CHARACTERISTICS:
Soil moisture - The soil moisture control section (4 to 12 inches) is dry throughout from June 1 to November 15 (168 days) and moist throughout from December 1 to May 1. The temperature exceeds 41 degrees F from April 1 to December 1 (245 days) and exceeds 47 degrees F from May 1 to November 25; Aridic moisture regime that borders on xeric.
Mean annual soil temperature - 48 to 52 degrees F.
Depth to base of argillic horizon - 20 to 40 inches.
Depth to horizons with free carbonates - 7 to 17 inches.
Depth to bedrock - 20 to 40 inches to a lithic contact.
Particle-size control section - Clay content: Averages 35 to 60 percent;
Sand content: 15 to 30 percent;
Rock fragments: 0 to 15 percent, mainly gravel. Lithology of fragments are volcanic rocks such as basalt or andesite.
Other features - Rock fragments on the surface, mostly cobbles and stones, range from 15 to 35 percent.
A horizon
Dry color: 10YR 5/2, 5/3, 6/2, 6/3 or 7.5YR 5/2.
Moist color: 10YR 3/2, 3/3, 4/2, 4/3 or 7.5YR 3/2 or 4/2.
Texture: Very cobbly silt loam, very cobbly loam, or very cobbly silty clay loam.
Clay content: 18 to 30 percent.
Rock fragments: 35 to 45 percent, mainly cobbles.
Reaction: Neutral or slightly alkaline.
Structure: Moderate medium platy, moderate medium subangular blocky, or granular.
BAt horizon
Dry color: 10YR 5/2, 5/3, 6/2, 6/3 or 7.5YR 5/2.
Moist color: 10YR 3/2, 3/3, 4/2, 4/3 or 7.5YR 3/2.
Texture: Silty clay loam or loam.
Clay content: 20 to 35 percent.
Rock fragments: 0 to 15 percent.
Reaction: Neutral through moderately alkaline.
Bt horizons
Dry color: 10YR 5/4, 6/3, 6/4; 7.5YR 5/2, 5/4, 6/2, 6/3 or 6/4.
Moist color: 10YR 4/3, 4/4; 7.5YR 3/4, 4/3, or 4/4.
Texture: Clay, clay loam, or silty clay.
Clay content: 35 to 60 percent.
Rock fragments: 0 to 15 percent.
Reaction: Slightly alkaline or moderately alkaline.
Effervescence: Slightly effervescent or strongly effervescent.
Calcium carbonate equivalent: 0 to 2 percent.
Other features: Some pedons have secondary carbonates segregated in fine filaments or threads; Some pedons have transitional BCt horizons or have a Bk horizon just above the bedrock.
COMPETING SERIES: These are the Buncelvoir, Farmell, Glasgow, Lanktree, Milkiway (T), Oppio, Risley, Schamp, and Trunk series.
Buncelvoir, Farmell, Lanktree, Milkiway, and Schamp soils are very deep. Glasgow soils have A horizons that are influenced by volcanic ash and have identifiable secondary carbonates in the lower part of the argillic horizon. Oppio soils do not have transitional BAt horizons in the upper part of the argillic horizon and are not effervescent in the argillic horizon. Risley soils are moderately deep to paralithic contacts. Trunk soils have more than 30 percent sand and average 15 to 35 percent rock fragments in the particle-size control section.
GEOGRAPHIC SETTING: Diaz soils are on lava plateaus. These soils formed in residuum and colluvium derived from basalt, andesite, or tuff. Slopes are 2 to 30 percent. Elevations range from 4,300 to 6,030 feet. The climate is semiarid with cold, moist winters and warm, dry summers. The mean annual precipitation is 8 to 12 inches including annual snowfall of 10 to 30 inches. The mean January temperature is 26 to 32 degrees F., the mean July temperature is 62 to 67 degrees F., and the mean annual temperature is 46 to 48 degrees F. The frost-free period is 80 to 110 days.
GEOGRAPHICALLY ASSOCIATED SOILS: These are the Brubeck, Horsecamp, Longcreek, Gerlach, and Ravendale soils. Brubeck, Horsecamp, Gerlach, and Ravendale soils have cracks that open to the surface every year. Longcreek soils are clayey-skeletal and shallow to lithic contacts.
DRAINAGE AND PERMEABILITY: Well drained; high surface runoff; slow permeability (moderately low or moderately high saturated hydraulic conductivity).
USE AND VEGETATION: Diaz soils are used for rangeland and wildlife habitat. The vegetation is mainly Wyoming big sagebrush, Thurber's needlegrass, Indian ricegrass, and bluebunch wheatgrass.
DISTRIBUTION AND EXTENT: Northeastern California, northwestern Nevada, and south-central Oregon. These soils are moderately extensive. MLRA 23.
MLRA SOIL SURVEY REGIONAL OFFICE (MO) RESPONSIBLE: Davis, California.
SERIES ESTABLISHED: Lake County (Southern Part), Oregon, 1991. The series was proposed from the Susanville Area Soil Survey, California, in 1965. The type location is currently in this survey area.
REMARKS: Diagnostic horizons and features recognized in this pedon are:
Ochric epipedon - The zone from the soil surface to 3 inches (A horizon).
Argillic horizon - The zone from 3 to 25 inches (BAt, Bt1, Bt2, and Bt3 horizons).
Lithic contact - The boundary at 25 inches to underlying hard bedrock (R layer).
Particle-size control section - The zone from 3 to 23 inches (BAt, Bt1, and Bt2 horizons and part of the Bt3 horizon).