LOCATION MAHOON OREstablished Series
TAXONOMIC CLASS: Fine, smectitic, mesic Aridic Palexerolls
TYPICAL PEDON: Mahoon very gravelly loam - rangeland, on a 33 percent slope at an elevation of 3900 feet. (Colors are for dry soil unless otherwise stated.)
A--0 to 3 inches; grayish brown (10YR 5/2) very gravelly loam, very dark grayish brown (10YR 3/2) moist; weak medium platy structure parting to moderate medium granular; slightly hard, very friable, slightly sticky and slightly plastic; many very fine and common fine and medium roots; common fine and medium, and few very fine and coarse vesicular pores; 50 percent gravel and 5 percent cobbles; neutral (pH 7.2); abrupt smooth boundary. (2 to 10 inches thick)
Bt1--3 to 9 inches; grayish brown (10YR 5/2) gravelly clay, very dark grayish brown (10YR 3/2) moist; weak medium subangular blocky structure parting to moderate medium granular; hard, friable, slightly sticky and slightly plastic; common very fine, fine and medium roots; common very fine, fine and medium irregular and tubular pores; common distinct clay films on faces of peds; 15 percent gravel and 5 percent cobbles; slightly alkaline (pH 7.4); abrupt smooth boundary. (3 to 8 inches thick)
2Bt2--9 to 18 inches; brown (10YR 5/3) gravelly clay, dark brown (10YR 3/3) moist; moderate medium prismatic structure parting to strong medium angular blocky; very hard, very firm, very sticky and very plastic; few very fine, fine and medium roots; few fine, medium and coarse irregular and tubular pores; common distinct and few prominent clay films on faces of peds; 20 percent gravel and 5 percent cobbles; slightly mildly alkaline (pH 7.6); clear smooth boundary. (2 to 10 inches thick)
2Bt3--18 to 25 inches; pale brown (10YR 6/3) gravelly clay, dark brown (10YR 4/3) moist; moderate coarse angular blocky structure parting to weak fine angular blocky; hard, firm, sticky and plastic; few very fine and fine roots; few very fine and medium, and common fine roots; common distinct clay films on faces of peds; 25 percent gravel and 5 percent cobbles; slightly alkaline (pH 7.8); gradual wavy boundary. (6 to 15 inches thick)
2Cr--25 to 35 inches; diatomaceous earth.
TYPE LOCATION: Harney County, Oregon, about 3 miles east of Drinkwater Pass, about 200 feet south and 2,300 feet west of the northeast corner of section 1, T. 21 S., R. 36 E., on the Petes Mountain quadrangle. (Latitude 43 degrees, 46 minutes, 44 seconds N., Longitude 118 degrees, 14 minutes, 22 seconds W. 1927 NAD)
RANGE IN CHARACTERISTICS: The soil is dry in 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 51 degrees F. The mollic epipedon is 7 to 12 inches thick. Between the A and Bt horizon there is an absolute clay increase of 15 to 20 percent. The thickness of the solum and depth to soft bedrock is 20 to 40 inches. The linear extensibility between the surface and bedrock is 4.0 to 6.0 centimeters. The particle-size control section averages 5 to 35 percent rock fragments mainly as gravels, and averages 40 to 50 percent clay.
The A horizon has values of 4 to 6 dry, 3 or 4 moist and chroma of 2 or 3 moist and dry. Rock fragment content is 10 to 60 percent and includes gravel and cobbles. Clay content is 18 to 27 percent. Reaction is neutral to slightly alkaline.
The Bt horizon has value of 4 to 6 dry, 2 to 5 moist and chroma of 2 to 4 moist and dry. Chroma of 4 and value of 6 dry and 4 or 5 moist occur in the lower part of the Bt. Rock fragment content is 0 to 35 percent. It is clay or clay loam with 35 to 45 percent clay in the upper part and clay with 40 to 60 percent clay in the lower part. Reaction is slightly to moderately alkaline.
COMPETING SERIES: These are the Barshaad and Simas soils. Barshaad soils are moderately deep over hard bedrock. Simas soils are greater than 40 inches to bedrock.
GEOGRAPHIC SETTING: Mahoon soils are on tablelands and hills and have slopes of 2 to 40 percent. The soils formed in residuum and colluvium from diatomaceous earth and tuffaceous sedimentary rocks. Elevation is 3,400 to 4,800 feet. The climate is characterized by cool, moist winters and hot, dry summers. The mean annual precipitation is 9 to 12 inches. The mean annual temperature is 45 to 49 degrees F. The frost free period is 80 to 100 days.
GEOGRAPHICALLY ASSOCIATED SOILS: These are the Cagle, Cotant, Gumble, and Risley soils. Cagle soils do not have the abrupt textural change and are on hills. Cotant and Gumble soils are shallow and are on hills. Risley soils lack a mollic epipedon and are on hills.
DRAINAGE AND PERMEABILITY: Well drained, slow permeability.
USE AND VEGETATION: The soils are used for livestock grazing and wildlife habitat. The potential native vegetation is Wyoming big sagebrush, bluebunch wheatgrass, Thurbers needlegrass, and Sandberg bluegrass.
DISTRIBUTION AND EXTENT: Southeastern Oregon; MLRA 10. Series is of small extent.
MLRA SOIL SURVEY REGIONAL OFFICE (MO) RESPONSIBLE: Portland, Oregon
SERIES ESTABLISHED: Harney County, Oregon, 1997.
REMARKS: Diagnostic horizons and features recognized in this pedon:
Mollic epipedon - from 0 to 9 inches (A, Bt1 horizons)
Pale- clay increase between the A and Bt horizons of about 17 percent (absolute) with an abrupt boundary
Argillic horizon - from 3 to 25 inches (Bt1, 2Bt2, 2Bt3 horizons)
Particle-size control section - from 3 to 23 inches (Bt1, 2Bt2, 2Bt3 horizons) averages about 47 percent clay and 20 percent rock fragments