Established Series


The Argonaut series consists of moderately deep, well drained soils that formed in materials weathered from meta-andesite. Argonaut soils are on foothills with slopes of 2 to 30 percent. The mean annual precipitation is 27 inches and the mean annual temperature is about 60 degrees F.

TAXONOMIC CLASS: Fine, mixed, superactive, thermic Mollic Haploxeralfs

TYPICAL PEDON: Argonaut gravelly loam-on a southwest facing slope of 6 percent under annual grass - oak cover at 1,360 feet elevation. (Colors are for dry soil unless otherwise stated. When described on March 24, 1959, the soil was slightly moist throughout.)

A1--0 to 2 inches; brown (7.5YR 5/4) gravelly loam, dark reddish brown (5YR 3/4) moist; weak thin platy structure; hard, friable, nonsticky and nonplastic; many very fine, few fine and medium roots; many very fine pores; 21 percent pebbles; slightly acid (pH 6.1); abrupt smooth boundary. (2 to 3 inches thick)

A2--2 to 6 inches; yellowish red (5YR 5/6) gravelly loam, yellowish red (5YR 3/6) moist, massive; hard, friable, nonsticky and slightly plastic; common very fine, few fine and medium roots; common very fine and fine, few medium pores; few thin clay films line pores; 20 percent pebbles, cobbles and stones; slightly acid (pH 6.3); clear smooth boundary. (3 to 8 inches thick)

Bt1--6 to 10 inches; yellowish red (5YR 4/6) gravelly heavy loam, yellowish red (5YR 3/6) moist, massive; hard, friable, slightly sticky and plastic; common very fine, few fine and medium roots; common very fine and fine medium pores; common thin clay films line most pores; 15 percent pebbles, cobbles and stones; slightly acid (pH 6.2); clear smooth boundary. (3 to 6 inches thick)

Bt2--10 to 14 inches; yellowish red (5YR 5/6) clay loam, yellowish red (5YR 3/6) moist; massive; hard, firm, slightly sticky and plastic; few fine and medium roots; common very fine and fine, few medium pores; continuous thin clay films line pores; about 8 percent pebbles and cobbles; slightly acid (pH 6.1); abrupt boundary. (3 to 5 inches thick)

Bt3--14 to 21 inches; brown (10YR 5/3) gravelly clay, yellowish brown (10YR5/4) and brown (7.5YR 5/4) moist; brown (7.5YR 5/4) coatings; massive; very hard, firm, sticky and very plastic; few very fine and coarse roots; few very fine pores; continuous thick clay films line pores; few slickenslides; about 22 percent pebbles, cobbles and stones; slightly acid (ph 6.1); abrupt wavy boundary. (4 to 17 inches)

Cr--21 to 27 inches; light reddish brown (2.5YR 6/4) deeply weathered meta-andesite, light olive brown moist, yellowish red (5YR 4/6) moderately thick, continuous clay films and black stains along a few fracture planes; the weathered rock crumbles when disturbed but is firmer with increasing depth; neutral (pH 7.1).

TYPE LOCATION: Amador County, California; about 0.5 miles west of Martell, 1,800 feet south and 1,500 feet east of the NE corner of sec 19, T. 6 N, R. 11 E. Jackson Quadrangle.

RANGE IN CHARACTERISTICS: Thickness of solum and depth to a paralithic contact is 20 to 40 inches. The mean annual soil temperature ranges from 59 to 67 degrees F. The soil between the depths of 8 and 24 inches or to a paralithic contact is dry in all parts from June 1 to October 15 (120 to 150 days) and is moist in all parts from November 15 to May 15 (165 to 195 days). Some rock fragments are present throughout the soil with about 2 to 25 percent in the lower Bt horizons and 5 to 35 percent in the A and upper Bt horizons. It has 2 to 6 percent organic matter in the upper 4 inches and more than 1 percent to a depth of 10 inches. The weighted average of the upper 20 inches of the Bt horizon is 35 to 50 percent.

The A horizon is 7.5YR 6/6, 5/6, 5/4, 4/6, 4/4; 5YR 5/3, 5/4, 5/6, 4/6, 4/4, or 4/6. Moist colors are 7.5YR 3/4, 4/4, 4/6; 5YR 3/4, 4/3, 4/4, or 4/6. The upper 4 inches have moist color values of 3. It is loam, silt loam or clay loam and may be gravelly or extremely stony. It is massive and hard or the upper few inches has weak platy, weak granular or weak subangular blocky structure. Reaction is moderately acid to neutral .

There is a transitional horizon between the A and B horizon or a gradual boundary occurs for the A horizon. The upper Bt horizon is 7.5YR 4/4, 4/6, 5/4, 5/6, 5/8; 5YR 5/3, 5/4, 5/6, 4/4, or 4/6. Moist colors are 7.5YR 4/4, 4/6; 5YR 4/4, 4/6, or 3/4. It is heavy loam, heavy silt loam, clay loam or its gravelly or cobbly equivalents. Reaction is moderately acid to neutral. An abrupt boundary is always present.

The lower Bt horizon is 10YR 5/3, 5/4, 5/6, 6/4; 7YR 5/4, 5/6, 4/6, 4/4; 5YR 4/6, 5/6, or 4/4. Moist colors are 10YR 5/3, 5/4, 5/6; 7.5YR 5/6, 5/4, 4/4, 4/6; 5YR 3/4, 4/4, 4/6, 4/8, or 5/6. It is heavy clay loam, gravelly clay or clay. Reaction is moderately acid to mildly alkaline. The clay increase between the upper Bt and lower Bt exceeds 15 percent. In some profiles a stone line separates these two horizons.

The Cr is 10YR 7/6, 2.5Y 7/4, or 6/4. Moist colors are 2.5Y 6/4 or 5/4.

COMPETING SERIES: These are the Conosta, Contra Costa, Francher, Kilaga, Phipps (T), and Trabuco. Conosta soils lack an argillic horizon with more than 15 percent clay increase within one inch. Contra Costa soils have a lithic contact between 20 and 40 inches. Francher soils have a CA/Mg ratio of less than 2:1. Kilaga and Phipps (T) soils are greater than 60 inches deep. Trabuco soils have a paralithic contact below 40 inches.

GEOGRAPHIC SETTING: The Argonaut soils are on undulating to hilly broad ridges and slightly concave slopes of 2 to 30 percent. The soils formed in material weathered from metamorphosed and intrusive basic rocks. Rock outcrops are common. Elevations are 200 to 2,500 feet. The climate is subhumid with hot dry summers and cool moist winters. Mean annual precipitation is 20 to 50 inches. Mean January temperature is about 44 degrees F.; mean July temperature is about 76 degrees F.; mean annual temperature is about 56 to 63 degrees F. Frost-free season ranges from 220 to 270 days.

GEOGRAPHICALLY ASSOCIATED SOILS: These are the Auburn, Rescue and Sobrante soils. Auburn soils lack argillic horizons. Rescue and Sobrante have less than 35 percent clay in all parts of the argillic horizon.

DRAINAGE AND PERMEABILITY: Well drained; slow to rapid runoff; very slow permeability.

USE AND VEGETATION: Mainly used for annual rangeland. Vegetation is soft chess, wild oats, ripgut brome, filaree with scattered foothill pine and scattered to dense thickets of blue oak, interior live oak and buckbrush.

DISTRIBUTION AND EXTENT: Foothills of the central Sierra Nevada in California. The series is of moderate extent.


SERIES ESTABLISHED: Amador County, California, Amador Area 1963.

REMARKS: Diagnostic horizons and features recognized in the pedon are:
Ochric epipedon - 0 to 6 inches (A1, A2)
Argillic horizon - 6 to 21 inches (Bt1, Bt2, Bt3)
Paralithic contact at 21 inches.

This pedon was sampled by NSSL at Riverside in 1959. Pedon number S59CA-3-6-(1-6)

OSED scanned by SSQA. Last revised by state on 8/85.

Edit log: 4/2003 Proposed edits for use in Butte County. Expand reaction A horizon: moderately acid to neutral. Expand reaction lower Bt horizon: from slightly acid to moderately acid. Add the following colors: A horizon-dry colors: 7.5YR 4/6 and 5YR 4/6. Upper Bt horizon-dry colors: 7.5YR 4/4, 4/6. Lower Bt horizon dry colors: 7.5YR 4/4, 4/6. Moist colors: 5YR 3/4. Cr horizon-dry: 10YR 7/6. Expand elevation from 300 to 200 feet. Expand MAT from 62 to 63 degrees F. Changed digger pine to foothill pine.

National Cooperative Soil Survey