LOCATION PARKFIELD CAEstablished Series
TAXONOMIC CLASS: Fine, smectitic, thermic Vertic Argixerolls
TYPICAL PEDON: Parkfield clay - summer fallow. (Colors are for dry soil unless otherwise stated.)
Ap--0 to 4 inches; brown (7.5YR 4/2) clay, dark brown (7.5YR 3/2) moist; moderate medium subangular blocky and moderate medium granular structure; hard, friable, very sticky, plastic; common very fine roots; many very fine tubular pores; medium acid (pH 6.0); clear smooth boundary. (4 to 8 inches thick)
A12--4 to 14 inches; brown (7.5YR 4/2) clay, dark brown (7.5YR 3/2) moist; weak coarse subangular blocky structure; hard, friable, very sticky, very plastic; common fine roots; common very fine tubular pores common thin clay films lining pores; slightly acid (pH 6.5); clear wavy boundary. (6 to 12 inches thick)
B2t--14 to 24 inches; dark brown (7.5YR 3/2 dry and moist) clay; moderate coarse angular blocky structure; extremely hard, friable, sticky, very plastic; common very fine roots; common very fine tubular pores; continuous thin clay films lining pores and common thick clay films on faces of peds; neutral (pH 7.0); abrupt wavy boundary. (8 to 16 inches thick)
IIC1--24 to 47 inches; pale olive (5Y 6/3) gravelly loam, olive brown (2.5Y 4/4) moist; massive; extremely hard, extremely firm, nonsticky, nonplastic; common very fine tubular and common very fine interstitial pores; many moderately thick clay films lining pores; neutral (pH 7.0); gradual wavy boundary. (22 to 24 inches thick)
IIC2--47 to 62 inches; light yellowish brown (10YR 6/4) gravelly loam, dark yellowish brown (10YR 4/4) moist; massive; hard, extremely firm, nonsticky, nonplastic; many very fine tubular, common very fine interstitial pores; many moderately thick clay films lining pores; neutral (pH 7.0).
TYPE LOCATION: Monterey County, California; about 2 miles southeast of Parkfield in the NW corner of the SW1/4NE1/4 sec. 31, T.23S., R.15E.
RANGE IN CHARACTERISTICS: Depth to a cemented C horizon regarded as a paralithic contact is 24 to 36 inches. Mean annual soil temperature is 60 degrees to 62 degrees F. and the soil temperature usually is never below 47 degrees F. Soil between depths of about 4 and 12 inches usually is dry all of the time from late April or May until November or early December and usually is continuously moist in some or all parts the rest of the year. Gravel and other rock fragments are from about 3 to 25 percent. During the summer the soil has cracks 1 to 2 inches wide at the surface that taper to about 1/4 to 1/2 inch wide at the bottom of the solum. Very few if any slickensides are present and intersecting slickensides are lacking. The A horizon is brown, dark brown, grayish brown or dark grayish brown in hue of 10YR or 7.5YR. It is silty clay, clay, clay loam or silty clay loam and has 35 to 43 percent clay. This horizon has moderate or strong subangular blocky structure. It is medium acid to neutral. Organic matter is 1 to 3 percent and decreases regularly with depth and is less than 1 percent below depth of 14 inches. The B2t horizon is brown, dark brown, yellowish brown or dark yellowish brown in 10YR or 7.5YR hue or dark reddish brown in 5YR hue. It is silty clay or clay with about 8 percent more clay than the A horizon. This horizon has moderate, coarse or medium angular blocky structure. It is neutral to moderately alkaline. The C horizon consists of weakly cemented, massive, stratified alluvium. After crushing, it is gravelly loam through gravelly clay and some pedons are cobbly. This horizon ranges from neutral to moderately alkaline. These underlying sediments are quite variable, ranging from light gray weakly consolidated calcareous material to grayish brown and reddish brown noncalcareous gravelly material with various degrees of cementation. In a few places the terrace deposits are only a few feet thick over unrelated sandstone and shale or serpentine. The C horizon is usually impervious to root and water penetration.
COMPETING SERIES: These are the Azule, Contra Costa, Henneke, Los Osos and Sespe series. Each of these soils lacks distinct cracks that extend to the surface. Azule and Contra Costa soils have ochric epipedons. Henneke soils have a lithic contact within a depth of 20 inches and have more than 35 percent rock fragments.
SETTING: The Parkfield soils are gently sloping to moderately steep and are on old terraces at elevations of 1,000 to 2,000 feet. They formed in fine and moderately fine textured alluvium from basic igneous, serpentine, and sedimentary sources over unrelated material. The climate is dry subhumid mesothermal with hot dry summers and cool moist winters. Mean annual precipitation is 13 to 20 inches. Average January temperature is 45 degrees F., average July temperature is about 72 degrees F., and the mean annual temperature is 58 degrees to 60 degrees F. The freeze-free season is 225 to 275 days.
PRINCIPAL ASSOCIATED SOILS: The Parkfield soils occur in the same general area as Alo, Climara, Millsholm, Montara, and Nacimiento soils. Alo and Climara soils have slickensides. Millsholm and Montara soils have lithic contacts at depths of less than 20 inches. Nacimiento soils lack cracks and an argillic horizon.
DRAINAGE AND PERMEABILITY: Well-drained; medium to rapid runoff; slow permeability.
USE AND VEGETATION: The Parkfield soils are used for range and growing dryland grain. Naturalized vegetation is annual grasses and forbs with few scattered blue oak, Digger pine, and scrub oak.
DISTRIBUTION AND EXTENT: Parkfield soils occur in the central Coast Range of California and are inextensive.
MLRA SOIL SURVEY REGIONAL OFFICE (MO) RESPONSIBLE: Davis, California
SERIES ESTABLISHED: Monterey County, California, 1972.
REMARKS: Parkfield soils would have been classified as (minimal) Brunizemic soils. Preliminary investigations show that the cemented C horizon does not meet requirements for a duripan.
OSED scanned by SSQA. Last revised by state on 11/72.