LOCATION TRISTAN NVEstablished Series
TAXONOMIC CLASS: Loamy-skeletal, mixed, superactive, mesic Aridic Argixerolls
TYPICAL PEDON: Tristan very cobbly loam--rangeland. (Colors are for dry soil unless otherwise noted.)
A1--0 to 3 inches; brown (7.5YR 4/2) very cobbly loam, dark brown (7.5YR 3/2) moist; moderate thick platy structure parting to moderate fine subangular blocky; soft, very friable, slightly sticky and slightly plastic; common very fine roots; few medium tubular, and many fine and very fine interstitial pores; 20 percent gravel, 15 percent cobbles, and 10 percent stones; slightly alkaline (pH 7.4); gradual smooth boundary. (2 to 4 inches thick)
A2--3 to 7 inches; brown (7.5YR 4/2) very stony loam, dark brown (7.5YR 3/2) moist; moderate medium and fine subangular blocky structure; slightly hard, friable, slightly sticky and slightly plastic; many fine and very fine roots; many fine and very fine tubular pores; 20 percent gravel, 10 percent cobbles, and 15 percent stones; neutral (pH 7.2); clear smooth boundary. (3 to 6 inches thick)
Bt1--7 to 11 inches; brown (7.5YR 4/2) very gravelly loam, dark brown 7.5YR 3/2) moist; strong medium subangular blocky structure; hard, friable, moderately sticky and moderately plastic; common fine through coarse roots; common fine tubular pores; many faint clay films on faces of peds and lining pores; 30 percent gravel and 10 percent cobbles; neutral (pH 7.0); gradual wavy boundary. (4 to 8 inches thick)
Bt2--11 to 17 inches; brown (7.5YR 5/2) very stony clay loam, dark brown (7.5YR 3/2) moist; strong medium and coarse subangular blocky structure; very hard, firm, moderately sticky and moderately plastic; common fine and medium roots; common fine tubular pores; many distinct clay films on faces of peds and lining pores; 10 percent gravel, 15 percent cobbles, and 20 percent stones; neutral (pH 7.0); clear wavy boundary. (5 to 10 inches thick)
Bt3--17 to 28 inches; brown (7.5YR 5/4) very gravelly clay loam, brown (7.5YR 4/4) moist; strong medium and coarse angular blocky structure; hard, friable, moderately sticky and moderately plastic; many very fine and fine roots; common fine and very fine tubular pores; many faint and distinct clay films on faces of peds and lining pores; 30 percent gravel, 5 percent cobbles, and 5 percent stones; neutral (pH 7.0); clear wavy boundary. (8 to 17 inches thick)
Bt4--28 to 49 inches; brown (7.5YR 5/4) extremely cobbly sandy clay loam, brown (7.5YR 4/4) moist; massive; hard, friable, slightly sticky and slightly plastic; many very fine through medium roots; common very fine and fine tubular pores; many faint and distinct clay films lining pores and bridging mineral grains; 20 percent gravel, 40 percent cobbles, and 20 percent stones; neutral (pH 7.0); gradual wavy boundary. (18 to 22 inches thick)
R--49 inches; highly fractured basaltic rock; soil and roots extend into the fractures.
TYPE LOCATION: Washoe County, Nevada; in the Pah Rah Range; approximately 900 feet east and 1,800 feet south of the northwest corner of section 35, T. 22 N., R. 22 E.; USGS Olinghouse 7.5 minute topographic quadrangle; 39 degrees 44 minutes 0.7 seconds north latitude and 119 degrees 29 minutes 12.6 seconds west longitude, NAD83.
RANGE IN CHARACTERISTICS:
Soil moisture - Usually moist during winter and spring, dry for 90 to 110 days during late summer and fall; Aridic moisture regime that borders on xeric.
Mean annual soil temperature - 47 to 53 degrees F.
Mollic epipedon thickness - 10 to 20 inches; includes the upper part of the argillic horizon.
Depth to bedrock - 40 to 60 inches to a lithic contact.
Particle-size control section - Clay content: 18 to 35 percent;
Rock fragments: 35 to 60 percent. Lithology of fragments are basalt and similar volcanic rocks.
Reaction - Neutral or slightly alkaline.
A horizons
Hue: 10YR or 7.5YR.
Value: 4 or 5 dry, 2 or 3 moist.
Chroma: 2 or 3, dry or moist.
Organic matter content: 1 or 2 percent.
Bt horizons
Hue: 10YR or 7.5YR.
Value: 4 through 6 dry, 3 or 4 moist.
Chroma: 2 through 4, dry or moist.
Texture: Loam or clay loam in the fine-earth fraction.
Rock fragments: 35 to 60 percent in the upper horizons; 60 to 80 percent in the lower horizons, mainly cobbles.
Structure: Angular or subangular blocky in some or all parts.
Organic matter content: 1 or 2 percent in the Bt1 and Bt2 horizons; less than 0.8 percent in the Bt3 and Bt4 horizons.
COMPETING SERIES: These are the Ashue, Badena, Badenaugh, Eaglerock, Gitabyte (T), Grinrod, Ister, Lemm, Leviathan, Nosrac, Oest, Searles, Searvar, Shawmount, Shree, Shroe, and Trid series.
Ashue soils have A and Bt horizons 13 to 30 inches thick and have unconformable very gravelly sand at a depth of 30 to 60 inches. Badena, Badenaugh, Lemm, Leviathan, Nosrac, Oest, Shawmount, Shree, and Shroe soils are very deep and do not have a lithic contact within 60 inches of the soil surface. Eaglerock, Gitabyte, Grinrod, Ister, Searles, Searvar, and Trid soils have bedrock at a depth of 20 to 40 inches.
GEOGRAPHIC SETTING: Tristan soils are on mountains. These soils formed in residuum and colluvium derived from basaltic rocks. Slopes are 15 to 50 percent. Elevations range from 5,000 to 7,500 feet. Soils at higher elevations occur on south-facing slopes. The climate is semiarid with cool, moist winters and warm, dry summers. The mean annual precipitation is 10 to 14 inches, the mean annual temperature is 44 to 50 degrees F., and the frost-free period is 80 to 100 days.
GEOGRAPHICALLY ASSOCIATED SOILS: These are the Arzo and Burnborough soils. Arzo soils are clayey and moderately deep to paralithic contacts. Burnborough soils are very deep and have a frigid temperature regime.
DRAINAGE AND PERMEABILITY: Well drained; moderately slow permeability (moderately high saturated hydraulic conductivity).
USE AND VEGETATION: Tristan soils are used for rangeland and wildlife habitat. The vegetation is Wyoming big sagebrush, Douglas rabbitbrush, bottlebrush squirreltail, antelope bitterbrush, and some Utah juniper.
DISTRIBUTION AND EXTENT: Western Nevada. These soils are moderately extensive. MLRA 26.
MLRA OFFICE RESPONSIBLE: Reno, Nevada.
SERIES ESTABLISHED: Washoe County (South Part), Nevada, 1980.
REMARKS: Diagnostic horizons and features recognized in this pedon are:
Mollic epipedon - The zone from the soil surface to 17 inches (A1, A2, Bt1, and Bt2 horizons).
Argillic horizon - The zone from 7 to 49 inches (Bt1, Bt2, Bt3, and Bt4 horizons).
Lithic contact - The boundary at 49 inches to underlying hard bedrock (R layer).
Particle-size control section - The zone from 7 to 27 inches (Bt1 and Bt2 horizons and part of the Bt3 horizon).