LOCATION TWICKENHAM OREstablished Series
TAXONOMIC CLASS: Fine, smectitic, mesic Vertic Paleargids
TYPICAL PEDON: Twickenham loam - rangeland, on a 9 percent, south-facing slope at an elevation of 1,700 feet. (Colors are for moist soils unless otherwise noted. When described on July 22, 1998, the soil was dry throughout.)
A--0 to 6 inches; brown (10YR 4/3) loam, light brownish gray (10YR 6/2) dry; weak medium subangular blocky structure; soft, very friable, slightly sticky and slightly plastic; few fine and common very fine roots; few fine and common very fine tubular pores; 5 percent gravel; neutral (pH 7.0); abrupt smooth boundary (2 to 8 inches thick)
2Bt1--6 to 13 inches; dark reddish brown (5YR 3/3) clay, reddish brown (5YR 4/3) dry; moderate medium and coarse angular blocky structure; very hard, very firm, very sticky and very plastic; few very fine roots; few fine and common very fine tubular pores; many prominent clay films on ped faces; 10 percent gravel; slightly alkaline (pH 7.5); clear smooth boundary.
3Bt2--13 to 19 inches; brown (7.5YR 4/3) silty clay loam, brown (7.5YR 5/4) dry; moderate medium and coarse angular blocky structure; hard, firm, moderately sticky and moderately plastic; few very fine tubular pores; common faint clay films on ped faces; 10 percent gravel; moderately alkaline (pH 8.3); clear wavy boundary (Combined thickness of the Bt horizon is 10 to 27 inches)
3Bk--19 to 60 inches; brown (7.5YR 4/4) very gravelly clay, light brown (7.5YR 6/4) dry; moderate medium subangular blocky structure; hard, firm, very sticky and very plastic; few very fine tubular pores; many fine soft powdery masses; carbonates coating all rock surfaces; 10 percent cobbles and 30 percent gravel; slightly effervescent; strongly alkaline (pH 8.5).
TYPE LOCATION: Wheeler County, Oregon, about 3/4 of a mile west of Camp Hancock; 300 feet east and 1,200 feet south of the NW corner of section 34, T. 7 S., R. 19 E. (Latitude 44 degrees, 55 minutes, and 08 seconds N. and Longitude 120 degrees, 26 minutes, and 26 seconds W)
RANGE IN CHARACTERISTICS: The soil is dry in all parts of the moisture control section for one-half to three-fourths of the time when the soil temperature is above 41 degrees F. The mean annual soil temperature is 47 to 54 degrees F. Depth to bedrock is greater than 60 inches. The particle-size control section is silty clay loam or clay with 35 to 60 percent clay and 10 to 35 percent rock fragments. An abrupt increase in clay of 15 to 30 percent or more exists between the A horizon and the 2Bt horizon. Coarse fragments are either basalt from the Columbia River Basalt flows or conglomerates from the Clarno Formation. The tuffaceous sediments of the John Day and Clarno Formations have hue of 5YR, 7.5YR, 10YR, 2.5Y with the hue of 5YR or 7.5YR the most common. The depth to secondary carbonates is 12 to 30 inches.
The A horizon has chroma of 2 or 3 moist and dry. It is loam or sandy loam with 8 to 27 percent clay It has 0 to 15 percent stones, 0 to 15 percent cobbles, and 5 to 40 percent gravel. It is neutral to moderately alkaline.
The 2Bt horizons have hue of 5YR to 2.5Y, value of 3 to 5 moist, 4 to 6 dry, and chroma of 3 or 4 moist and dry. It is silty clay loam or clay with 35 to 60 percent clay. It has 0 to 15 percent cobbles and 0 to 15 percent gravel. It is slightly or moderately alkaline.
The Btk horizon (when present) has hue of 5YR to 2.5Y, value of 3 to 5 moist, 4 to 6 dry and chroma of 2 to 4 moist and dry. It is clay or silty clay loam with 35 to 50 percent clay. It has 10 to 30 percent cobbles and 5 to 15 percent gravel.
The 3Bk horizon has hue of 5YR to 2.5Y, value of 4 to 6 moist, 5 to 7 dry, and chroma of 3 or 4 moist and dry. It is clay loam or clay with 30 to 45 percent clay. It has 0 to 25 percent stones, 0 to 30 percent cobbles, and 0 to 30 percent gravel, but averages 15 to 50 percent total rock fragments. Some pedons have 0 to 20 percent paragravels in the lower part of the horizon.
COMPETING SERIES: These are the Acoma, Berdugo, Biscaro, Borda, Bowns, Brent, Chardoton, Deodar, Gooding, Hagata, Jowec, Locey, Lodico, Mahala, Phing, Poall, Reba, Sorf, Spangenburg, and Verdico soils. Acoma soils have over 45 percent sand in the control section and are neutral or slightly alkaline in the surface horizons. Berdugo soils have a C horizon with stratified loam, loamy sand, sandy loam, or sand. Biscaro soils are moderately deep to paralithic contact and have a weakly, silica-cemented Bq horizon, Borda soils have 0 to 10 percent coarse fragments in the control section, slightly acid or neutral reaction in the solum, and are 40 to 60 inches to bedrock. Bowns soils are moderately deep to bedrock and have a neutral reaction in the solum. Brent soils have an E horizon and are neutral or slightly alkaline in the solum. Chardoton soils have an E horizon and have a neutral reaction in the surface horizons. Deodar soils have an AB horizon and are less than 45 percent clay in the upper part of the argillic horizon. Gooding soils have an E horizon and are deep to a duripan. Hagata soils are moderately deep to a paralithic contact and have a neutral reaction in the surface horizons. Jowec soils are slightly acid or neutral in the surface horizons and have a solum 15 to 25 inches thick. Locey soils are moderately deep to bedrock and are non-calcareous throughout the profile. Lodico soils are moderately deep to bedrock and have a neutral reaction in the surface horizons. Mahala soils are moderately deep to a paralithic contact and have an E horizon. Phing soils have an E horizon and have silica coatings on ped faces in the Bq horizon. Poall soils have a Bk horizon with very fine sandy loam, fine sandy loam, or silt loam textures and the Bk horizon lacks any coarse fragments. Reba soils have a slightly acid or moderately acid reaction in the surface horizons and the Bk horizon has more than 50 percent sand. Sorf soils are moderately deep to a paralithic contact and have a neutral or slightly alkaline reaction in the surface horizons. Spangenburg soils have a neutral or slightly alkaline reaction in the surface horizons and the depth to the stratified C horizon is 30 to 50 inches. Verdico soils are moderately deep to a paralithic contact and have a slightly acid to slightly alkaline reaction throughout the profile.
GEOGRAPHIC SETTING: Twickenham soils are on south slopes and rolling ridgetops. They formed in clayey colluvium weathered from tuffaceous sediment of the John Day and Clarno Formations. Slopes range from 2 to 60 percent. Elevation is 1,350 to 3,800 feet. The mean annual temperature is 47 to 52 degrees F. and the mean annual precipitation is 9 to 12 inches. The frost-free period is 90 to 150 days.
GEOGRAPHICALLY ASSOCIATED SOILS: These are the Day, Buffaran, Gwinly, Simas, and the Cooperopolis, and the competing Sorf soil. Day soils are on saddles and sideslopes, are in the very-fine family, and have intersecting slickensides. Buffaran soils are on fan piedmont remnants and are shallow to a duripan. Gwinly soils are on convex sideslopes near rock outcrops, are clayey-skeletal, and are shallow to bedrock. Simas soils are on north slopes and have a mollic epipedon. Cooperopolis soils are on gently sloping, north slopes, are in the loamy family, and are shallow to bedrock.
DRAINAGE AND PERMEABILITY: Well drained; very slow permeability
USE AND VEGETATION: Used for livestock grazing and wildlife habitat. Native vegetation is shadscale, bluebunch wheatgrass, sand dropseed, and basin big sagebrush.
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 ESTABLISHED: John Day Fossil Beds National Monument, Oregon, 2000.
REMARKS: Diagnostic horizons and features recognized in this pedon -
Ochric epipedon - 0 to 6 inches (A horizon)
Argillic horizon - 6 to 19 inches (2Bt1 and 3Bt2 horizons)
secondary carbonates - 19 to 60 inches (3Bk horizon)
Particle-size control section - 6 to 19 inches (2Bt1 and 3Bt2 horizons)
Xeric intergrade
ADDITIONAL DATA: Partial laboratory data is available for this soil. Reference sample is S98OR-069-004 from Wheeler County, Oregon to NSSL, Lincoln, NE.