LOCATION TOURN CAEstablished Series
TAXONOMIC CLASS: Ashy-skeletal, glassy, frigid Vitrandic Argixerolls
TYPICAL PEDON: Tourn ashy sandy loam--forestland. (Colors are for dry soil unless otherwise noted). The surface is partially covered with about 0.25 inch of pine needles.
A1--0 to 3 inches; brown (7.5YR 4/2) ashy sandy loam, dark brown (7.5YR 3/2) moist; moderate very fine subangular blocky structure; soft, very friable, nonsticky and nonplastic; many very fine and few fine roots; many very fine interstitial pores; moderately acid (pH 5.8); clear wavy boundary. (1 to 4 inches thick).
A2--3 to 7 inches; brown (7.5YR 4/2) ashy sandy loam, dark brown (7.5YR 3/2) moist; moderate very fine adn fine subangular blocky structure; soft, friable, nonsticky and nonplastic; many very fine, and common fine roots; many very fine interstitial pores; moderately acid (pH 5.8); clear wavy boundary. (2 to 6 inches thick).
BA--7 to 20 inches; brown (7.5YR 4/2) ashy sandy loam, dark brown (7.5YR 3/2) moist; weak medium subangular blocky structure; slightly hard, very friable, slightly sticky and slightly plastic; many very fine through medium and common coarse roots; many very fine interstitial pores; few faint clay films bridging mineral grains; moderately acid (pH 5.8); clear smooth wavy. (5 to 12 inches thick).
Bt--20 to 37 inches; brown (7.5YR 5/4) very gravelly ashy loam, brown (7.5YR 4/3) moist; weak fine and medium subangular blocky structure; slightly hard, friable, moderately sticky and moderately plastic; few fine, medium and coarse roots; many very fine interstitial pores; few faint clay films lining pores and bridging mineral grains; 50 percent hard volcanic gravel; moderately acid (pH 5.8); abrupt wavy boundary. (8 to 14 inches thick).
Cr--37 to 47 inches; gray (N 6/) weathered tuff.
TYPE LOCATION: Lassen County, California; on the Modoc National Forest in the Warner Mountains about 0.3 mile south of Sunflower Knob; about 1800 feet south and 1900 feet west of the northeast corner of section 23, T. 39 N., R. 15 E.; USGS Emerson Peak 7.5 minute topographic quadrangle; 41 degrees 12 minutes 14 seconds north latitude and 120 degrees 14 minutes 03 seconds west longitude, NAD27.
RANGE IN CHARACTERISTICS:
Soil moisture - These soils are usually moist in winter, spring, and early summer, dry later in summer and fall; xeric soil moisture regime.
Mean annual soil temperature - 43 to 46 degrees F.
Mean summer soil temperature - 60 to 63egrees F.
Mollic epipedon thickness - 12 to 20 inches.
Oxalate Al + 1/2 oxalate iron: 0.2 to 0.4 percent.
Volcanic glass content - 50 to 80 percent in the coarse silt through fine sand fractions.
Depth to bedrock - 22 to 40 inches to a paralithic contact. The paralithic materials below the contact are weathered glassy tuff.
Reaction - Moderately acid or slightly acid.
Particle-size control section - Clay content: Averages 18 to 27 percent.
A horizons - Hue: 10YR or 7.5YR.
Value: 3 through 5 dry, 2 or 3 moist.
Chroma: 2 or 3, dry or moist.
Organic matter content: 1 to 4 percent.
BA horizon - Hue: 5YR or 7.5YR.
Clay content: 10 to 15 percent.
Rock fragments: 5 to 15 percent.
Organic matter content: 1 or 2 percent.
Structure: Moderate or strong, fine or medium subangular blocky.
Bt horizon - Hue: 10YR or 7.5YR.
Texture: Ashy loam or ashy sandy clay loam.
Clay content: 20 to 30 percent.
Rock fragments: 40 to 60 percent.
Structure: Moderate or strong, fine to coarse subangular blocky.
COMPETING SERIES: These are the Chesebro (T)(OR), Eep, Lyonman and Monasterio. Chesebro and Eep are very deep. Lyonman soils are very gravelly or very cobbly throughout. Monasterio soils are moderately deep to a lithic contact and have a Btq horizon with silica pendants on undersides of rocks.
GEOGRAPHIC SETTING: Tourn soils are on mountains. They formed in volcanic ash, and alluvium and residuum derived from glassy tuff. Slopes are 2 to 15 percent. Elevations range from 6,500 to 8,000 feet. The climate is subhumid with cold, moist winters and warm, dry summers. The mean annual precipitation is 20 to 25 inches most of which comes as snow. The mean annual temperature is 43 to 45 degrees F., and the mean summer temperature is about 56 degrees F. The frost-free period is 50 to 80 days.
GEOGRAPHICALLY ASSOCIATED SOILS: These are the Longval and competing Lyonman soils. Longval soils have 5 to 12 percent clay in the particle size control section, are very deep and are cryic.
DRAINAGE AND PERMEABILITY: Well drained; low or medium surface runoff; moderate permeability.
USE AND VEGETATION: Tourn soils are used for timber production, watershed, wildlife habitat, and limited livestock grazing. The vegetation consists of an open forest canopy of ponderosa pine with an understory of mountain big sagebrush, antelope bitterbrush, snowberry, mountain brome, Idaho fescue, slender wheatgrass, and bluegrasses.
DISTRIBUTION AND EXTENT: Northeastern California. These soils are not extensive with about 1,500 acres of the series mapped to date. MLRA 21.
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, 1971.
REMARKS: The revision of December 2004 changes the classification to Ashy-skeletal, glassy, frigid Vitrandic Argixerolls based on re-description of the recovered type location. This change better represents the soil series as mapped presently.
The revision of January 2004 updates the taxonomic class from Medial Xeric Haplocryands, changes temperature regime to frigid, updates horizon designations, and recognizes the presence of an argillic horizon.
Mollic epipedon - The zone from the soil surface to 20 inches (A1, A2 and the BA horizons).
Vitrandic intergrade feature - The zone from the soil surface to 37 inches (A1, A2, BA, and the Bt horizons).
Argillic horizon - The zone from 20 to 37 inches (Bt horizon).
Paralithic contact - The boundary at 37 inches to underlying soft, weathered bedrock (Cr layer).
Particle-size control section - The zone from 20 to 37 inches (Bt horizon).