LOCATION SWEEK ORTentative Series
TAXONOMIC CLASS: Very-fine, smectitic, mesic Chromic Haploxererts
TYPICAL PEDON: Sweek silty clay - rangeland, on a 19 percent, west-facing slope at an elevation of 3,623 feet. (When described on August 4, 2003, the soil was dry to 24 inches and slightly moist below. Colors are for moist soil unless otherwise noted.)
A--0 to 1 inch; brown (7.5YR 4/3) silty clay, brown (7.5YR 4/4) dry; strong very fine and fine granular structure; hard, firm, very sticky and very plastic; few fine and common very fine roots; few fine and many very fine irregular pores; neutral (pH 7.2); abrupt smooth boundary. (1 to 3 inches thick)
BA--1 to 9 inches; dark reddish brown (5YR 3/4) clay, reddish brown (5YR 4/4) dry; strong coarse prismatic structure parting to moderate coarse angular blocky; very hard, very firm, very sticky and very plastic; few fine and very fine roots; few fine and very fine tubular pores; slightly alkaline (pH 7.4); gradual wavy boundary. (0 to 10 inches thick)
Bss1--9 to 17 inches; dark reddish brown (5YR 3/4) clay, reddish brown (5YR 4/4) dry; strong medium and coarse angular blocky structure; very hard, very firm, very sticky and very plastic; few medium, fine, and very fine roots; few fine and very fine tubular pores; common distinct slickensides on ped faces; moderately alkaline (pH 8.1); gradual wavy boundary.
Bss2--17 to 25 inches; dark reddish brown (2.5YR 3/4) clay, reddish brown (2.5YR 4/4) dry; strong medium angular blocky structure; extremely hard, extremely firm, very sticky and very plastic; common prominent slickensides on ped faces; moderately alkaline (pH 8.2); clear wavy boundary. (The combined thickness of the Bss horizon is 14 to 20 inches.)
Bssk--25 to 60 inches; dark reddish brown (2.5YR 3/4) clay, reddish brown (2.5YR 4/4) dry; moderate medium angular blocky structure; very hard, very firm, very sticky and very plastic; few very fine roots; few very fine tubular pores; common distinct slickensides on ped faces; strongly effervescent secondary carbonates in soft masses; moderately alkaline (pH 8.4).
TYPE LOCATION: Grant County, Oregon, located about 1 mile SW of the community of Hamilton on the west side of Cottonwood Road just north of the cinder pit; 10 feet east and 2,000 feet south of the northwest corner of section 2, T. 10 S., R. 28 E. (Latitude 44 degrees, 43 minutes, and 53.00 seconds North and Longitude 119 degrees, 19 minutes, and 42.56 seconds West)
RANGE IN CHARACTERISTICS: Sweek soils have cracks 5 mm or more that open and close once each year and remain open for 90 to 120 consecutive days (July through September). The mean annual soil temperature is 47 to 52 degrees F. Depth to weathered sediments of the John Day Formation is 40 to over 60 inches. Depth to secondary carbonates is 20 to 30 inches. The red hue found throughout the profile is derived from the red geologic member of the John Day Formation. The particle-size control section averages 60 to 75 percent clay. Soil reaction is neutral to slightly alkaline in the surface horizon and slightly alkaline to moderately alkaline in the subsoil.
The A horizon has hue of 5YR or 7.5YR, value of 2 or 3 moist, 3 to 5 dry, and chroma of 2 through 6 moist and dry. It is silty clay with 40 to 55 percent clay. It has 0 to 30 percent stones, 0 to 20 percent cobbles, and 0 to 15 percent gravel.
The BA, Bss1, and Bss2 horizons have hues of 5YR, 2.5YR, or 10R, values of 3 or 4 moist and dry, and chromas of 3 through 6 moist and dry. Soil structure is angular blocky or very coarse and coarse prismatic parting to angular blocky. Slickensides are common or many and distinct or prominent. It is clay with 60 to 75 percent clay.
The Bssk horizon has colors similar to the BA, Bss1, and Bss2 horizons. Secondary carbonates occur as filaments or as soft masses. Slickensides are few or common. It is clay with 55 to 70 percent clay. It has 0 to 5 percent cobbles and 0 to 15 percent gravel.
COMPETING SERIES: These are the Ager, Agerdelly, Beirman, and Day series. The Ager soils are 40 to 60 inches deep to paralithic siltstone and mudstone. Agerdelly soils have carbonates at a depth of 30 to 44 inches and have hue of 10YR or 2.5Y. Beirman soils have carbonates at a depth of 10 to 20 inches. Day soils have open cracks for 120 to 150 consecutive days.
GEOGRAPHIC SETTING: Sweek soils are on rolling hills and have slopes of 2 to 50 percent. These soils formed in the clayey sediments of the John Day Formation. Elevations are 2,200 to 4,600 feet. The climate is characterized by cool wet winters and hot dry summers. The mean annual precipitation is 12 to 16 inches, and the mean annual temperature is 45 to 50 degrees F. The frost-free period is 80 to 120 days.
GEOGRAPHICALLY ASSOCIATED SOILS: These are the Cupper, Drybed, Hack, Haystack, Patron, and Wylie (T) series. All these soils have less than 60 percent clay. Cupper soils are on fans and are in the ashy over loamy family. Drybed soils have an aridic moisture regime, are fine-loamy, and occur at lower elevations. Hack soils are on fans and are fine-loamy. Haystack soils have an aridic moisture regime, are loamy-skeletal, and occur at lower elevations. Patron soils vitrandic properties in the surface layers and are on north-facing slopes. Wylie soils are shallow to a paralithic contact and are found on sideslopes near exposures of Badlands.
DRAINAGE AND PERMEABILITY: Well drained; very slow permeability.
USE AND VEGETATION: Livestock grazing and wildlife habitat. The potential native vegetation is low sage, Sandbergs bluegrass, and western juniper.
DISTRIBUTION AND EXTENT: East-central Oregon, MLRA B-10. This series is of small extent.
MLRA SOIL SURVEY REGIONAL OFFICE (MO) RESPONSIBLE: Portland, Oregon
SERIES PROPOSED: Grant County, Oregon, 2004. The name is derived from Sweek Canyon.
REMARKS: Diagnostic horizons and features recognized in this pedon are:
Ochric epipedon
Cambic horizon - from 9 to 25 inches (Bss1 and Bss2 horizons)
Secondary carbonates - 25 to 60 inches (Bssk horizon)
Particle size control section - from 10 to 40 inches (lower part of the AB horizon, Bss1, Bss2, and the upper part of the Bssk horizon)