LOCATION ARNOLD CAEstablished Series
TAXONOMIC CLASS: Mixed, thermic Typic Xeropsamments
TYPICAL PEDON: Arnold loamy sand, rangeland. (Colors are for dry soil unless otherwise noted.)
O1--1/2 inch to 0; incomplete cover of twigs and leaves.
A1--0 to 2 inches; light brownish gray (10YR 6/2) loamy sand, dark gray (10YR 4/1) moist; weak fine granular structure; soft and very friable; common fine roots; many very fine and few fine interstitial pores; many fine flakes of organic matter; medium acid (pH 6.0); clear wavy boundary. (1 to 5 inches thick)
A2--2 to 12 inches; light brownish gray (10YR 6/2) loamy sand, dark grayish brown (10YR 4/2) moist; massive when moist, single grained and loose when dry; soft and very friable; few very fine and medium roots; many very fine interstitial pores; medium acid (pH 6.0); diffuse smooth boundary. (8 to 14 inches thick)
A3--12 to 23 inches; light brownish gray (10YR 6/2) sand, dark grayish brown (10YR 4/2) moist; slightly lighter color than horizon above; massive when moist, single grained and loose when dry; soft, very friable; few very fine and medium roots; many very fine interstitial pores; strongly acid (pH 5.5); few indistinct pockets filled with C horizon material; gradual wavy boundary. (6 to 14 inches thick)
C1--23 to 39 inches; very pale brown (10YR 8/3) sand, brown (10YR 5/3) moist; massive when moist, single grained and loose when dry; soft, very friable; few very fine roots; many very fine interstitial pores; 3 percent hard sandstone fragments; strongly acid (pH 5.1); few indistinct pockets filled with A horizon material; gradual smooth boundary. (10 to 18 inches thick)
C2--39 to 55 inches; very pale brown (10YR 8/3) sand, pale brown (10YR 6/3) moist; massive when moist, single grained and loose when dry; soft, very friable; few fine roots; many very fine interstitial pores; 3 percent hard sandstone fragments; strongly acid (pH 5.5); few indistinct pockets filled with A horizon material; gradual wavy boundary. (12 to 19 inches thick)
C3r--55 to 64 inches; very pale brown (10YR 7/3) soft sandstone, near reddish yellow (7.5YR 6/6) moist; very easily cut with hand tools, only slightly more firm than horizon above; contains 10 percent of subangular pieces, 2 to 8 inches in diameter of brown (7.5YR 5/4) hard sandstone, yellowish red (5YR 5/6) moist; continuous moderately thick clay films in bridges and lining pores of hard fragments; fragments are extremely firm when moist in the upper portions to firm moist at depths over 60 inches; indistinct pockets filled with A horizon material.
TYPE LOCATION: Santa Barbara County, California; southeast of Orcutt, California; 2 1/4 miles SE from Clark Road on Bradley Road into oil field, 0.2 miles past cattle guard, 70 feet up 48 percent slopes; SW portion of NE 1/4 NE 1/4 sec. 24, T.9N., R.33W.
RANGE IN CHARACTERISTICS: Depth to a paralithic contact of soft sandstone that excludes roots is 40 to 60 inches or more. The mean annual soil temperature at a depth of 20 inches is 59 degrees to 63 degrees F., and the lowest temperature is about 47 degrees F. Soil between the depths of about 12 to 36 inches usually is moist in some or all parts from November until sometime in May and is dry all the rest of the year. In many pedons, the pH is near 6.0 throughout, but the range is from neutral to strongly acid with no large change from top to bottom. The profile is sand or loamy sand throughout. A few pedons have 1 to 15 percent gravel. Slopes are complex and range from 9 to 75 percent.
The A horizon is dark grayish brown to light brownish gray and pale brown (10YR 4/2, 5/2, 5/3, 6/2, 6/3). Where present, the darker colors are confined to the upper 3 to 8 inches. Organic matter content averages 0.5 to 1.0 percent in the upper 10 inches and decreases regularly with increasing depth.
Horizons immediately below the A horizons may be identified as B horizons or as C horizons. These horizons in some pedons are 10YR 8/1, 8/2, 8/3, 8/4, 7/1, 7/2, 7/3, 7/4, 6/2, or 6/3. In other pedons, they are 10YR 6/4, 5/3, 5/4, 5/6, 5/8, 4/4, 4/6, 3/4, 3/6; 7.5YR 6/4. In still other pedons, the ground mass has a pale color with high value and low chroma, but there are 5 to 30 percent lumps and small masses of higher chroma and redder hue. Boundaries between colors are clear to diffuse. Portions of horizons with stronger colors have a few thin clay bridges and are slightly more firm and harder when dry than the pale portions. On the average, clay increase to the brighter parts is less than 3 percent absolute. Some pedons, usually in the average, clay increase to the brighter parts is less than 3 percent absolute. Some pedons, usually in the lower part, contain a few hard dark reddish brown concretions or hard lumps suggestive of relic pieces of duripan. A small amount of cementation by silica is present, but most of the cementing material seems to be clay. These hard pieces do not slake in water and most do not soften appreciably.
COMPETING SERIES: These are the Briones, Calhi, Corralitos, Delhi, Monoridge, Monvero and Tujunga series. Briones soils have a paralithic contact at a depth of 20 to 40 inches. Calhi and Delhi soils formed in wind deposited material and have a fairly uniform texture throughout the profile. Further, Calhi soils are calcareous throughout. Corralitos and Tujunga soils lack the slowly permeable paralithic contact below depth of 40 inches and are stratified with textures coarse than loamy fine sand. Monoridge soils are moderately deep to a paralithic contact. Monvero soils are very deep and effervescent throughout.
GEOGRAPHIC SETTING: Arnold soils are on hills and hilly uplands at elevations of 100 to 2,500 feet. Slopes are 9 to 75 percent. The soils formed in material weathered from soft sandstone. Some of the sandstone may be a relic of a cemented sandy soil. The climate is dry subhumid mesothermal with warm dry somewhat foggy summers and cool moist winters. Mean annual precipitation is 12 to 23 inches. Snow is very rare. Average annual temperature is 57 degrees to 62 degrees F.; average January temperature is about 51 degrees F.; average July temperature is about 63 degrees F. The frost-free season is about 175 to 330 days.
GEOGRAPHICALLY ASSOCIATED SOILS: These are the competing Corralitos soils and the Chamise, Elkhorn, Oceano, San Andreas, Santa Lucia, Santa Ynez and Tierra soils. Chamise, Elkhorn, Santa Ynez and Tierra soils have B2t horizons with more than 18 percent clay. Oceano soils have thin lamellae. San Andreas soils have sandy loam, fine sandy loam or loam textures with less than 18 percent clay, and dark colored A horizons with more than 1 percent organic matter. Santa Lucia soils average more than 35 percent clay and more than 35 percent rock fragments between depths of 10 to 40 inches.
DRAINAGE AND PERMEABILITY: Somewhat excessively drained; very low to medium runoff; rapid permeability above the sandstone and slow in the sandstone.
USE AND VEGETATION: Used mostly for range, very limited areas used for growing truck crops, Christmas trees, and improved pasture. Vegetation is mostly chaparral, coastal sagebrush, coast live oak, shrubs, annual grasses, and forbs.
DISTRIBUTION AND EXTENT: South-central part of the Coast Range in California, usually within 30 miles of the coast. Moderately extensive. MLRA 15, 19, 20.
MLRA SOIL SURVEY REGIONAL OFFICE (MO) RESPONSIBLE: Davis, California
SERIES ESTABLISHED: Modesto-Turlock Area, California, 1908. (Redefined Santa Barbara County, 1927).
REMARKS: The Arnold series was redefined to include soils of the Moro Cojo series, which in part were the pedons with stronger chroma in the lower part.