LOCATION OROGNEN CAEstablished Series
TAXONOMIC CLASS: Fine, mixed, superactive, thermic Typic Palexeralfs
TYPICAL PEDON: Orognen sandy loam - on a west-facing slope of 3 percent at an elevation of 1,760 feet under annual barley, soft chess, and ripgut brome. (Colors are for dry soil unless otherwise stated. When described on August 23, 1981, the soil was dry to 19 inches and slightly moist below).
A1--0 to 2 inches; light brown (7.5YR 6/4) sandy loam, brown (7.5YR 4/4) moist; weak medium coarse platy and subangular blocky structure; slightly hard, friable, slightly sticky and slightly plastic; common very fine roots; common very fine tubular pores; slightly acid (pH 6.2); clear smooth boundary.
A2--2 to 11 inches; light brown (7.5YR 6/4) sandy loam, brown (7.5YR 4/4) moist; weak medium subangular blocky structure; slightly hard, friable, slightly sticky and slightly plastic; common very fine roots; common very fine tubular pores; neutral (pH 6.8); clear smooth boundary.
A3--11 to 16 inches; light brown (7.5YR 6/4) sandy loam, yellowish red (5YR 4/6) moist; weak medium and coarse subangular blocky structure; slightly hard, friable, slightly sticky and plastic; few very fine roots; common very fine tubular pores; neutral (pH 7.0); clear smooth boundary. (Combined thickness of the A horizon is 12 to 19 inches)
Bt1--16 to 19 inches; reddish brown (5YR 4/4) sandy clay loam, yellowish red (5YR 4/6) moist; strong medium and coarse prismatic structure; slightly hard, friable, slightly sticky and plastic; few very fine roots; few very fine tubular pores; common thin and few moderately thick clay films on peds and bridging sand grains; neutral (pH 7.1); abrupt smooth boundary. (0 to 9 inches thick)
2Bt2--19 to 34 inches; reddish brown (5YR 4/4) clay, yellowish red (5YR 4/6) and reddish yellow (7.5YR 6/6) moist; strong medium, coarse and very coarse prismatic structure; hard, very firm, sticky and very plastic; few very fine and fine roots; few very fine tubular pores; continuous thick clay films on peds and bridging sand grains; moderately alkaline (pH 7.9); clear smooth boundary. (10 to 18 inches thick)
2BCt1--34 to 52 inches; yellowish red (5YR 4/6) gravelly clay loam, yellowish red (5YR 4/6) and brown (7.5YR 4/4) moist; massive; slightly hard, firm, sticky and plastic; few very fine tubular pores; common moderately thick clay films bridging sand grains; 25 percent gravel 2 to 5mm in size; moderately alkaline (pH 8.0); gradual smooth boundary. (10 to 20 inches thick)
2BCt2--52 t 62 inches; yellowish red (5YR 4/6) gravelly clay loam, yellowish red (5YR 4/6, 5/8) moist; massive; slightly hard, firm, sticky and plastic; few very fine tubular pores; common thin and moderately thick clay films bridging sand grains; 25 percent gravel 2 to 5mm in size; moderately alkaline (pH 8.0).
TYPE LOCATION: Merced County, California; about 20 miles SW of the city of Los Banos, 1 mile north of Merced-San Benito County boundary, 3,000 feet east of south fork of Los Banos Creek, 100 feet west of dirt road, 2,600 feet south and 300 feet east of the NW corner of sec. 12, T. 13 S., R. 8 E.
RANGE IN CHARACTERISTICS: The moisture control section of 8 to 19 inches is moist throughout from about November 15 to May 15 and dry throughout from about June 15 to October 15 in most years. The soil temperature is below 47 degrees F from January 1 to February 15. Mean annual soil temperature is 59 degrees to 62 degrees F. The soil is noneffervescent throughout. The solum thickness ranges from 40 inches to more than 60 inches thick.
The A horizon dry color is 7.5YR 5/4, 6/4, 7/4; 10YR 5/3 or 6/4. Moist colors are 5YR 4/6; 7.5YR 3/4, 4/4, 5/4; 10YR 3/2, 3/3 or 4/4. Organic matter is less than 1 percent. It is sandy loam in the upper part and sandy loam, loam, sandy clay loam, or gravelly sandy clay loam in the lower part. It has 10 to 25 percent clay content. Gravel content ranges from 0 to 20 percent. Reaction is slightly acid to mildly alkaline in the upper part and neutral or mildly alkaline in the lower part.
The Bt horizon dry color is 5YR 4/4, 4/6; 7.5YR 4/4, 4/6 or 5/4. Moist colors are 5YR 4/4, 4/6; or 7.5YR 4/4. It is gravelly sandy clay loam, sandy clay loam, sandy loam or loam with 15 to 25 percent clay content. There is only a slight increase in clay content and is less than 1.2 times than the horizon above. Gravel content ranges from 0 to 20 percent. Reaction is neutral to moderately alkaline.
The 2Bt horizon dry color is 5YR 4/4, 4/6; 7.5YR 4/4, or 4/6. Moist colors are 5YR 4/4, 4/6; 7.5YR 4/4, 5/4, or 6/6. It is clay loam, sandy clay, or clay with 35 to 60 percent clay content and at leasts 15 percent more clay (absolute) within 1 inch than the horizon above. Gravel content ranges from 0 to 10 percent. Reaction is neutral to moderately alkaline.
The 2BCt horizon dry color is 5YR 4/6, 5/4; 7.5YR 4/6, or 5/4, 5/6. Moist colors are 5YR 4/6, 5/8; 7.5YR 4/4, 4/6, 5/4, or 4/6. It is gravelly sandy clay loam, gravelly clay loam, or clay loam with 30 to 50 percent clay content. Gravel content ranges from 10 to 35 percent. Reaction is mildly alkaline or moderately alkaline.
COMPETING SERIES: These are the Cometa, Corning, Hytop, Millsap and Yokayo series. Cometa soils have sola less than 40 inches thick and have less than 10 percent gravel throughout the Bt horizons. Corning soils have moderately acid or strongly acid reactions. Millsap soils are 20 to 40 inches deep to a lithic contact. Yokayo soils have 10YR and 2.5Y hues in the argillic horizon, are neutral to moderately acid.
GEOGRAPHIC SETTING: Orognen soils are on high elevation dissected terraces and hillslopes of these terraces and have slopes of 2 to 50 percent. Elevations are 700 to 1,800 feet. These soils formed in alluvium from sedimentary and metamorphic rock of the Peckham Formation. The climate is subhumid with hot dry summers and cool moist winters. The mean annual precipitation is about 13 to 21 inches. Mean January temperature is about 45 degrees F; mean July temperature is about 75 degrees F; mean annual temperature is about 61 degrees F. Frost-free period is 190 to 240 days.
GEOGRAPHICALLY ASSOCIATED SOILS: These are the Contra Costa, Fifield, and Quiensabe soils. These soils have a lithic contact within 20 to 40 inches of the surface.
DRAINAGE AND PERMEABILITY: These soils are used mainly for annual livestock grazing. The vegetation is soft chess, wild oats, Mediterranean barley, ripgut brome, filaree, tarweed, and other annual grasses and forbs.
DISTRIBUTION AND EXTENT: These soils are on high terraces in intermountain valleys of the Coast Range. They are not extensive.
MLRA SOIL SURVEY REGIONAL OFFICE (MO) RESPONSIBLE: Davis, California
SERIES ESTABLISHED: Merced County, California 1984.
REMARKS: These soils were formerly mapped as Positas in the Los Banos Area, series 1939 report. They are being differentiated by having less than 1 percent organic matter and being noneffervescent. pH determined by colorimetric method using Thymol Blue and Hellige-Truog triplex indicators. Texture determined by modified Bouyoucos method. Organic matter assumed to be less than 1 percent. Base saturation determined by KC1-triethanolamine extract (sum of cations).
Diagnostic horizons and features recognized in this pedon are:
Ochric epipedon- the zone from 0 to 16 inches (A1, A2, A3)
Argillic horizon- the zone from 16 to 62 inches (Bt1, 2Bt2, 2BCt1, 2BCt2)