LOCATION THOMHILL CAEstablished Series
TAXONOMIC CLASS: Fine-loamy, mixed, superactive, thermic Calcic Haploxerolls
TYPICAL PEDON: Thomhill loam on a southwest slope of 2 percent, under barley stubble from a crop that was harvested in the fall of 1983, at 2330 feet elevation (colors are for dry soil unless otherwise stated. When described on September 9, 1984, the soil was slightly moist below 2 inches.)
Ap--0 to 2 inches; grayish brown (2.5Y 5/2) loam, very dark grayish brown (2.5Y 3/2) moist; cloddy; hard, friable, slightly sticky and slightly plastic; common very fine roots; common very fine interstitial and few fine tubular pores; moderately alkaline (pH 8.0); clear smooth boundary. (2 to 8 inches thick)
A--2 to 13 inches; grayish brown (2.5Y 5/2) loam, very dark grayish brown (2.5Y 3/2) moist; medium moderate and coarse subangular blocky structure; slightly hard and hard, friable, slightly sticky and slightly plastic; common very fine roots; common very fine tubular and few very fine interstitial pores; moderately alkaline (pH 8.0); gradual smooth boundary. (8 to 12 inches thick)
AB--13 to 22 inches; light brownish gray (2.5Y 6/2) loam, dark grayish brown (2.5Y 4/2) moist; massive; slightly hard, friable, slightly sticky and slightly plastic; few very fine roots; common very fine tubular and interstitial and few fine tubular pores; moderately alkaline (pH 8.0); clear wavy boundary. (0 to 13 inches thick)
Bk1--22 to 26 inches; light brownish gray (2.5Y 6/2) loam, dark grayish brown (2.5Y 4/2) moist; massive; slightly hard, friable, sticky and slightly plastic; few very fine roots; common very fine tubular and interstitial and few fine tubular pores; strongly effervescent with carbonates disseminated; moderately alkaline (pH 8.0); clear wavy boundary. (4 to 10 inches thick)
Bk2--26 to 34 inches; light brownish gray (2.5Y 6/2) loam, dark grayish brown (2.5Y 4/2) moist; massive; slightly hard, friable, sticky and slightly plastic; few very fine roots; common very fine interstitial and many very fine tubular pores; strongly effervescent with carbonates disseminated and segregated into few fine filaments; moderately alkaline (pH 8.0); gradual wavy boundary.
Bk3--34 to 40 inches; light brownish gray (2.5Y 6/2) loam, dark grayish brown (2.5Y 4/2) moist; massive; slightly hard, friable, sticky and slightly plastic; few very fine roots; common very fine interstitial and many very fine tubular pores; strongly effervescent with carbonates disseminated and segregated into common fine filaments; moderately alkaline (pH 8.0);gradual wavy boundary.
Bk4--40 to 53 inches; light brownish gray (2.5Y 6/2) loam, dark grayish brown (2.5Y 4/2) moist; massive; slightly hard, friable, sticky and slightly plastic; few very fine roots; common very fine interstitial and many very fine tubular pores; strongly effervescent with carbonates desseminated and segregated into many fine filaments; moderately alkaline (pH 8.0); gradual wavy boundary.
Bk5--53 to 64 inches; light gray (2.5Y 7/2) loam, grayish brown (2.5Y 5/2) moist; massive; slightly hard, friable, sticky and slightly plastic; few very fine roots; common very fine interstitial and tubular pores; strongly effervescent with carbonates disseminated and segregated into common fine filaments; moderately alkaline (pH 8.0). (The combined thickness of the Bk horizon is 25 to 55 inches)
TYPE LOCATION: San Luis Obispo County, California; 1,780 feet south and 1,350 feet west of the northeast corner of section 13, T. 29 S., R. 18 E., USGS Las Yeguas Ranch Topographic Quadrangle; lat. 35 degrees, 24 minutes, 18 seconds N. and long. 119 degrees, 59 minutes, 27 seconds W.
RANGE IN CHARACTERISTICS: The mean annual soil temperature is 60 to 67 degrees F. The soil between the depths of 8 and 21 inches is moist in some part from December 15 until May 1 and is moist in all parts for at least 45 consecutive days. The soil is dry in all parts for about 210 days and has a xeric moisture regime bordering on aridic. Gravel content is 0 to 5 percent throughout the profile. Clay content is 20 to 30 percent throughout the profile.
The A horizon has dry color of 10YR 5/2 or 5/3; 2.5Y 5/2 or 5/3 and moist color of 10YR 3/2 or 3/3; 2.5Y 3/2 or 3/3. It is slightly or moderately alkaline. Textures are loam or clay loam.
The AB horizon has color of 10YR 6/2 or 7/2; 2.5Y 6/2 or 7/2. Moist color is 10YR 4/2, 4/3, 4/4, 5/4; 2.5Y 4/2, 4/3, 4/4. It is strongly or violently effervescent.
The C horizon has dry color of 10YR 6/2 or 7/2; 2.5Y 6/2 or 7/2 and moist color of 10YR 4/2, 4/3, 4/4, 5/4; 2.5Y 4/2, 4/3, 4/4. It is strongly or violently effervescent with carbonates disseminated and segregated as few to many fine filaments or soft masses. Textures are loam, silt loam or clay loam. Some pedons have sandy loam strata in the lower part.
COMPETING SERIES: These are the Apollo, Domengine, Fontana, Nacimiento, Sorrento and Woo series. Apollo, Sorrento and Woo soil are moist throughout there moisture control section for about 120 days. Domengine, Nacimiento and Fontana soils are moderately deep.
GEOGRAPHIC SETTING: Thomhill soils are on alluvial flats and alluvial fans. Slopes are 0 to 9 percent. They formed in alluvium from mixed sources. Elevations are 1,900 to 2,400 feet. The climate is semiarid with hot dry summers and cool moist winters. Mean annual precipitation is 8 to 10 inches. Mean January temperature is about 46 degrees F, the mean July temperature is about 77 degrees F and the mean annual temperature is 58 to 62 degrees F. Frost-free season is 175 to 200 days.
GEOGRAPHICALLY ASSOCIATED SOILS: These are the Beam (T), Jenks (T), Panoza (T), Yeguas (T) and Polonio soils. Beam (T) soils are less than 20 inches to a paralithic contact. Jenks (T) and Panoza (T) soils are 20 to 40 inches to paralithic contact. Yeguas (T) soils have an argillic horizon. Polonio soils have an ochric epipedon and are calcareous throughout.
DRAINAGE AND PERMEABILITY: Well drained. Runoff is negligible to medium. Permeability is moderate.
USE AND VEGETATION: The soil is used for dry farmed small grain crops and some livestock grazing.
DISTRIBUTION AND EXTENT: The Carrizo Plain in California, MLRA 17. The series is not extensive.
MLRA SOIL SURVEY REGIONAL OFFICE (MO) RESPONSIBLE: Davis, California
SERIES PROPOSED: San Luis Obispo County, California; Carrizo Plain Area, 1985. Soil name was coined.
REMARKS: Diagnostic horizons and features recognized in this pedon are:
Mollic epipedon: The zone from the surface of the soil to a depth of 13 inches (Ap,A horizons). Organic carbon is 1.20 percent in the Ap and 0.71 percent in the A horizon and decreases regularly with depth. 1.2 Base saturation is 97 to 100 percent.
Bk horizons: The zone with secondary carbonates within a depth of 1.1 meters. (Bk1, Bk2, Bk3, Bk4 horizons 24 to 64 inches)
ADDITIONAL DATA: NSSL Pedon No. 84P 930