LOCATION ZACA CAEstablished Series
TAXONOMIC CLASS: Fine, smectitic, thermic Vertic Haploxerolls
TYPICAL PEDON: Zaca clay, cultivated. (Colors are for dry soil unless otherwise noted.
Ap--0 to 4 inches, very dark gray (10YR 3/1) clay very dark gray (10YR 3/1) when moist; strong, fine and medium, granular structure; very hard, friable, very sticky and very plastic; common very fine roots; many very fine interstitial pores; moderately alkaline (pH 8.0); slightly effervescent with lime disseminated; clear, smooth boundary. 1 to 4 inches thick.
A12--4 to 16 inches, very dark gray (10YR 3/1) clay,
very dark gray (10YR 3/1) when moist; strong, medium and coarse, subangular blocky and weak, fine, granular structure; very hard, friable, very sticky and very plastic; many very fine roots; many very fine interstitial and few very fine tubular pores; moderately alkaline (pH 8.0); strongly effervescent with lime disseminated; gradual, wavy boundary. 10 to 16 inches thick.
A13--16 to 36 inches, very dark gray (10YR 3/1) clay, very dark gray (10YR 3/1) when moist; strong, fine, subangular blocky and medium, fine, granular structure; very hard, friable, very sticky and very plastic; common very fine roots; many very fine interstitial and few very fine tubular pores; moderately alkaline (pH 8.0); slightly effervescent with lime disseminated; many slickensides on peds; clear, irregular boundary. 9 to 25 inches thick.
Cca--36 to 54 inches; mixed very dark grayish brown 10YR 3/2) and yellowish brown (10YR 5/4) silty clay, very dark brown (10YR 2/2) and dark yellowish brown (10YR 4/4) when moist; moderate, fine, subangular blocky and moderate, fine, granular structure, hard, friable, very sticky and plastic; few very fine roots; many very fine interstitial pores; moderately alkaline (pH 8.0); violently effervescent with lime disseminated and segregated in large irregularly shaped soft masses; clear, wavy boundary. 20 to 25 inches thick.
Cr--54 to 72 inches; yellowish brown (10YR 5/4) softly consolidated mudstone that crushes to sandy clay loam, dark yellowish brown (10YR 4/4) when moist; massive; hard, friable, sticky and plastic; no roots; many very fine interstitial pores; moderately alkaline (pH 8.0); violently effervescent with lime segregated in medium irregularly shaped soft masses.
TYPE LOCATION: San Luis Obispo County, California; in Nipomo Valley about 1,550 feet north and 3,100 feet east of the intersection of Thompson Avenue and Mehlaschu Road, T.11N., R.34W.
RANGE IN CHARACTERISTICS: Depth to a paralithic contact of softly consolidated marine sediments is 40 to 65 inches. The mean annual soil temperature is about 60 degrees to 64 degrees F., and usually is not below 47 degrees F. at any time. The soil between depths of 4 to 12 inches is usually dry all of the time from May until November and is moist in some or all parts all the rest of the year. The soil has cracks more than 1 cm wide to a depth of 20 inches or more when dry and lacks intersecting slickensides. The soils are slightly to strongly effervescent in their upper horizons and violently effervescent in their lower horizons.
The A horizon has hue of 10YR, value of 3 through 5 and chroma of less than 1.5 moist. It is clay or silty clay. The uppermost few inches are granular and remainder of the A horizon has subangular of angular blocky ore granular structure.
The C horizon has hue of 10YR, value of 3 through 5 and chroma of 1 or 2, but includes chroma of 4 in some pedons.
The Cr horizon is white, light yellowish brown, or yellowish brown in hue of 10YR, or brown or olive brown in the hue 2.5Y. It is strongly or violently effervescent.
COMPETING SERIES: These are the Ayar, Diablo, Linne, and Nacimiento series. Ayar soils have intersecting slickensides and chroma of 2 or more in the A horizon. Diablo soils have noncalcareous surface horizons and have intersecting slickensides. Linne soils are less than 40 inches deep to a paralithic contact and do not crack widely upon drying. Nacimiento soils have 25 to 35 percent clay and are less than 40 inches deep to paralithic contact.
GEOGRAPHIC SETTING: Zaca soils are 5 to 75 percent are on gently rolling to very steep slopes at elevations of 200 to 2,000 feet. They formed in softly consolidated marine sediments of mudstone, sandstone and shale. The climate is subhumid mesothermal with warm dry summers and moist cool winters. Mean annual precipitation is 15 to 22 inches. Average January temperature is 50 degrees F.; average July temperature is 67 degrees to 72 degrees F.; mean annual temperature is 58 to 62 degrees F. The frost-free season is 300 to 350 days.
GEOGRAPHICALLY ASSOCIATED SOILS: These are the competing Diablo and Ayar soils and the Santa Lucia soils. Santa Lucia soils have a lithic contact at depths of 20 to 40 inches and have more than 35 percent coarse fragments.
DRAINAGE AND PERMEABILITY: Well drained; medium to rapid runoff; slow permeability.
USE AND VEGETATION: Used for range, dryland grain and beans, irrigated orchards, and for urban development. The native vegetation is annual grasses and forbs.
DISTRIBUTION AND EXTENT: Scattered throughout the coast range in central and southern California. The soils are of moderate extent.
MLRA OFFICE RESPONSIBLE: Davis, California
SERIES ESTABLISHED: Santa Barbara County (Santa Ynez
Area), California, 1927.
REMARKS: The Zaca soils were formerly classified as Rendzinas or Grumusols with some characteristics of Rendzinas. The type location has been moved back to San Luis Obispo County because it is more extensive in this locality.
OSED scanned by SSQA. Last revised by state on 9/74.