LOCATION HAMBRIGHT CAEstablished Series
TAXONOMIC CLASS: Loamy-skeletal, mixed, superactive, thermic Lithic Haploxerolls
TYPICAL PEDON: Hambright very stony loam - on a south facing slope of 55 percent in an area that was severely burned in the summer of 1981. Vegetation is scrub oak, laurel, and annual grasses at 960 feet elevation. (Colors are for dry soil unless otherwise stated. When described on June 13, 1983, the soils were dry from 0 to 1 inch, slightly moist from 1 to 6 inches and wet from 6 to 12 inches.
A--0 to 1 inch, dark grayish brown (10YR 4/2) very stony loam, dark brown (7.5YR 3/2) moist; weak fine and medium granular structure; soft, very friable, nonsticky and nonplastic; many very fine roots; many very fine tubular and interstitial pores; 50 percent pebbles, cobbles, and stones; moderately acid (pH 5.6); clear smooth boundary.
AB--1 inch to 6 inches; brown (10YR 4/3) very stony loam, dark reddish brown (5YR 3/2) moist; weak fine subangular blocky structure; slightly hard, friable, nonsticky and slightly plastic; common very fine roots; many very fine tubular pores; 60 percent pebbles, cobbles, and stones; moderately acid (pH 5.6);clear wavy boundary.
Bw--6 to 12 inches, dark brown (7.5YR 4/4) very stony loam, dark reddish brown (5YR 3/2) moist; weak fine and medium subangular blocky structure; slightly hard, friable, nonsticky and slightly plastic; common very fine roots; many very fine tubular pores; 60 percent pebbles, cobbles, and stones; moderately acid (pH 5.6); abrupt wavy boundary.
R--12 inches, fractured basic igneous bedrock.
TYPE LOCATION: Napa County, California; 2 1/2 miles NE on Atlas Peak Road from intersection of Westgate Drive, at the north end of the Silverado Country Club golf course; 100 feet west of Atlas Peak Road in the NE1/4NE1/4, sec. 13, R. 4 W., T. 6 N.
RANGE IN CHARACTERISTICS: Solum thickness and depth to a lithic contact is 10 to 20 inches. Mean annual soil temperature varies from 59 degrees to 65 degrees F and is not below 41 degrees F at any time. The soils to a depth of 10 inches or the bedrock are dry in May or early June to October or early November for 130 to 150 days. The soils have rock fragments throughout and consist of gravel, cobbles, and stones. The fragments make up from 15 to 75 percent of the soil or occur on the surface. The soils are slightly acid or moderately acid. It is loam or silt loam with 20 to 27 percent clay content.
The A horizon is 10YR 4/2, 4/3; 7.5YR 4/2, 4/4, 5/2; 5YR 4/3, 4/4, 5/3, or 5/4. Moist color is 10YR 3/2; 7.5YR 3/2; 5YR 3/2 or 3/3. It has weak to strong granular or subangular blocky structure when dry. Organic matter content ranges from 2 to 8 percent.
The Bw horizon has similar range of properties as the A horizon except 10YR hues excluded. It typically has a very slight clay increase or redder hues than the A horizon. Some pedons have a few clay films.
COMPETING SERIES: These are the Temblor series in the same family and the Friant, Inks, Lodo, Lopez and Toomes series in other families. Friant and Lodo soils have less than 35 percent rock fragments. Inks soils have argillic horizons. Lopez soils have chroma of less than 2, have base saturation of 50 to 75 percent, and have formed from siliceous shales. Temblor soils are neutral to moderately alkaline throughout and have formed in diatomaceous or siliceous shales. Toomes soils lack a mollic epipedon and have less than 35 percent rock fragments.
GEOGRAPHIC SETTING: Hambright soils are on hillslopes of plateaus and basalt flows. Slopes are 2 to 75 percent. The soils formed in material weathered from basic igneous rocks, mainly basalt. Elevations are 300 to 3,000 feet. Hambright soils are commonly mapped in complex with rock outcrop. The climate is subhumid with hot dry summers and cool moist winters. Mean annual precipitation is 20 to 40 inches. Mean January temperature is 42 degrees F; mean July temperature is 76 degrees F; and mean annual temperature varies from 56 to 62 degrees F. Frost-free season is 160 to 260 days.
GEOGRAPHICALLY ASSOCIATED SOILS: These are the competing Toomes soils and the Forward, Gilroy, Guenoc, Kidd, and Sobrante soils. Forward soils are 20 to 40 inches deep and have more than 60 percent pyroclastic materials. Gilroy, Guenoc, and Sobrante soils are 20 to 40 inches deep and have argillic horizons. Kidd soils are mesic and have more than 60 percent pyroclastic materials.
DRAINAGE AND PERMEABILITY: Well drained; medium to very rapid runoff; moderate permeability.
USE AND VEGETATION: Used for grazing. Vegetation is annual grasses and forbs with a few blue oaks and shrubs.
DISTRIBUTION AND EXTENT: In the Coast Range of California where the soils are moderately extensive.
MLRA SOIL SURVEY REGIONAL OFFICE (MO) RESPONSIBLE: Davis, California
SERIES ESTABLISHED: Glenn County, California 1957.
REMARKS: Hambright soils were originally mapped in Glenn County. However, because of the low acreage, the soils were correlated to the Toomes series. The name Hambright was used for soils mapped in Lake, Napa, Solano, San Diego and Ventura counties. In San Diego Soil Survey Report, the soils are a taxadjunct because they are brighter, have a more clayey subsoil and few rock fragments throughout the profile. In Ventura County, Hambright soils include clay loams and soils that would now be recognized as having an argillic horizon. The concept of the soil now is one that has a mollic epipedon, more than 35 percent rock fragments and has loam or silt loam textures with no or only slight increases in clay content. The series is now described with properties that only include the series ranges as mapped in Lake, Napa, and Solano counties.
The activity class was added to the classification in February of 2003. Competing series were not checked at that time. - ET