LOCATION POLONIO CAEstablished Series
TAXONOMIC CLASS: Fine-loamy, mixed, superactive, thermic Calcic Haploxerepts
TYPICAL PEDON: Polonio clay loam, rangeland. (Colors are for dry soil unless otherwise stated.)
Ap--0 to 6 inches; light brownish gray (10YR 6/2) clay loam, brown (10YR 4/3) moist; weak coarse subangular blocky structure; hard, friable, slightly sticky and plastic; few very fine roots; common very fine tubular pores; slightly effervescent with disseminated lime; moderately alkaline (pH 8.0); gradual wavy boundary. (6 to 11 inches thick)
A--6 to 14 inches; pale brown (10YR 6/3) clay loam, brown (10YR 4/3) moist; moderate fine subangular blocky; slightly hard, friable, slightly sticky and plastic; few very fine roots, common very fine and fine tubular pores; slightly effervescent with disseminated lime; moderately alkaline (pH 8.0); gradual wavy boundary. (5 to 19 inches thick)
Bk1--14 to 49 inches; light yellowish brown (10YR 6/4) clay loam, dark yellowish brown (10YR 4/4) moist; moderate medium subangular blocky structure; slightly hard, friable, slightly sticky and plastic; few very fine roots; few very fine and fine tubular pores; strongly effervescent with segregated lime as many fine lime filaments and seams; moderately alkaline (pH 8.0); gradual wavy boundary. (7 to 35 inches thick)
Bk2--49 to 69 inches; brown (7.5YR 5/4) clay loam, dark brown (7.5YR 4/4) moist; moderate medium subangular blocky structure, slightly hard, friable, slightly sticky and plastic; few very fine tubular pores; few thin clay films lining pores; violently effervescent with segregated lime as many fine lime filaments and seams; moderately alkaline (pH 8.0).
TYPE LOCATION: San Luis Obispo County, California; in McDonald Canyon about 600 feet west and 1,700 feet north of the SE corner of Section 33, T.27S., R.15E; USGS Camatta Canyon Topographic Quadrangle; lat. 35 degrees, 31 minutes, 56 seconds N. and long. 120 degrees, 21 minutes, 24 seconds W.
RANGE IN CHARACTERISTICS: The mean annual soil temperature is about 59 degrees to 62 degrees F., and is always above 47 degrees F. The soils are moist from about December 15 until about May 15; but in 6 out of 10 years, they are never moist in some parts between depths of 6 and 18 inches for 90 consecutive days. The soils have less than 30 percent coarse sand. The sands are rounded rather than angular. Gravel content is 0 to 35 percent throughout
The A horizon has a dry color of 10YR 5/1, 5/2, 5/3, 6/1, 6/2 or 6/3. Moist color is 10YR 4/1, 4/2, 4/3, 5/1, 5/2 or 5/3. It is clay loam, silty clay loam, silt loam or loam. This horizon is slightly hard or hard.
The Bk horizon has a dry color of 7.5YR 5/4; 10YR 5/4, 6/3, 6/4, 7/2, 7/3, 7/4, 8/3, 8/4. Moist color is 7.5YR 4/4; 10YR 4/2, 4/3, 4/4, 5/4, 6/2, 6/3, or 6/4. It is clay loam, silty clay loam, loam or heavy sandy loam or sandy clay loam. This horizon is slightly hard or hard.
COMPETING SERIES: These are the Chanac, Exclose, Paver, and Vernalis series. Chanac and Vernalis soils have Bt horizons. Exclose has slopes of 30 to 65 percent. Paver and Vernalis soils do not have carbonates above 20 inches.
GEOGRAPHIC SETTING: Polonio soils are on alluvial fans and have gradients of 0 to 9 percent. They formed in calcareous alluvium derived from sedimentary rock sources. Elevations are 1,050 to 2,500 feet. The climate is semiarid with warm, dry summers and cool, moist winter. The mean annual precipitation is 6 to 10 inches. Average January temperature is about 46 degrees F.; the average July temperature is about 73 degrees F.; and the mean annual temperature is about 57 degrees to 61 degrees F. Frost-free season is 175 to 250 days.
GEOGRAPHICALLY ASSOCIATED SOILS: These are the Balcom, Calleguas, and Camatta soils. Balcom soils have a solum 20 to 40 inches thick underlain by soft calcareous shale. Calleguas soils have a solum 12 to 20 inches thick underlain by weathered calcareous shale. Camatta soils have a solum 8 to 20 inches thick underlain by a petrocalcic horizon.
DRAINAGE AND PERMEABILITY: Well drained; negligible to medium runoff; moderately slow permeability.
USE AND VEGETATION: The soils are used for range and dry farmed grain. Vegetation is mainly redstem filaree, soft chess, red brome, foxtail barley, burclover.
DISTRIBUTION AND EXTENT: Valleys of the south end of Diablo Range, California, MLRA 17. The soils are of moderate extent.
MLRA SOIL SURVEY REGIONAL OFFICE (MO) RESPONSIBLE: Davis, California
SERIES ESTABLISHED: San Luis Obispo County, California, Paso Robles Area, 1977.