LOCATION MOKELUMNE CAEstablished Series
TAXONOMIC CLASS: Fine, kaolinitic, thermic Typic Haploxerults
TYPICAL PEDON: Mokelumne gravelly loam - on a 6 percent convex southwest facing slope at 240 feet elevation under scattered blue oak and annual grasses and forbs. When described September 8, 1983, the soil was dry to 12 inches and slightly moist below. (Colors are for dry soil unless otherwise stated).
A1--0 to 6 inches; pinkish gray (7.5YR 6/2) gravelly loam, brown (7.5YR 4/4) moist; massive; hard, friable, slightly sticky and nonplastic; many very fine roots; many very fine tubular and interstitial pores, few fine tubular pores; 25 percent subrounded pebbles 1/2 to 2 inches in size; slightly acid (pH 6.5); clear smooth boundary.
A2--6 to 10 inches; light brown (7.5YR 6/4) gravelly loam, brown (7.5YR 5/4) moist; massive; slightly hard, very friable, sticky and slightly plastic; common very fine roots; many very fine interstitial, common very fine and few fine tubular pores; few thin clay films bridging mineral grains; 30 percent subrounded pebbles and 5 percent cobbles; strongly acid (pH 5.5); clear wavy boundary. (combined thickness of A horizon is 7 to 19 inches)
2Bt1/E--10 to 12 inches; light red (2.5YR 6/6) clay with pink (5YR 7/3) coatings, red (2.5YR 5/6) with reddish brown (5YR 5/3) coatings when moist; weak medium subangular blocky structure; very hard, firm, very sticky and plastic; common very fine exped roots; common very fine tubular pores; many thin clay films lining ped faces and common thin clay films lining pores; E tongues into 2Bt2; 5 percent subrounded pebbles; strongly acid (pH 5.2); clear irregular boundary. (1 to 4 inches thick)
2Bt2--12 to 20 inches; variegated light reddish brown (5YR 6/4) and red (2.5YR 5/6) clay, reddish brown (5YR 5/4) and red (2.5YR 5/8) moist; weak medium subangular blocky structure; very hard, firm, very sticky and plastic; common very fine exped roots; common very fine tubular pores; many thin clay films lining ped faces and few thin clay films lining pores; 5 percent subrounded pebbles, base saturation, 19 percent (Lincoln lab) very strongly acid (pH 5.0); clear wavy boundary.
2Bt3--20 to 31 inches; variegated pink (5YR 7/4), reddish yellow (5YR 7/6) and 15 percent white (2.5Y 8/2) clay, light reddish brown (5YR 6/4), reddish yellow (5YR 6/6) and light gray (2.5Y 7/2) moist; weak medium subangular blocky structure; very hard, firm, very sticky and slightly plastic; common very fine, few fine exped roots, common coarse roots; common very fine tubular pores; many thin and few moderately thick clay films lining ped faces, few thin clay films lining pores; surface material in cracks less than 2 mm wide between peds; very strongly acid (pH 4.5); gradual wavy boundary. (combined thickness of the 2Bt horizons is 5 to 22 inches)
2BCt--31 to 39 inches; variegated white (N 8/0) -50 percent, pink (5YR 7/4) and light reddish brown (5YR 6/4) clay, light gray (N 7/0), light reddish brown (5YR 6/4) and reddish brown (5YR 5/4) moist; weak medium subangular blocky structure; very hard, firm, sticky and slightly plastic; common coarse roots; few very fine tubular pores; few moderately thick and common thin clay films on ped faces; very strongly acid (pH 4.5); clear wavy boundary. (4 to 17 inches thick)
2Cr--39 to 46 inches; variegated white (N 8/0) -85 percent, yellow (10YR 8/6) and light reddish brown (5YR 6/4) weakly consolidated clayey sediments, light gray (N 7/0), yellow (10YR 7/6) and reddish brown (5YR 5/4) moist; few fine tubular pores; very few thin clay films along fractures; very strongly acid (pH 4.5).
TYPE LOCATION: Sacramento County, California; about 3 miles east of Bridgehouse, 0.26 miles south of the intersection of Highway 16 and Ione Road, 0.34 miles east along a ranch road and 125 feet north of the road; 2,400 feet north and 540 feet east of the southwest corner section 7, T.7 N., R.9 E.
RANGE IN CHARACTERISTICS: Depth to paralithic contact is 20 to 40 inches. The mean annual soil temperature is 64 to 67 degrees F at 20 inches and remains above 47 degrees F throughout the year. The soil is dry between 8 inches and the paralithic contact in most years from June 1 to October 15, moist in all parts from December 1 to May 1 and moist in some part for the rest of the year. Weighted average clay content of the textural control section is 35 to 70 percent. Clay content of the argillic horizon decreases by 20 to 30 percent of the maximum above the paralithic contact. Base saturation ranges from 15 to 35 percent throughout the argillic horizon. Content of weatherable minerals in the 20 to 200 micron faction of the upper 20 inches of the argillic horizon is less than 10 percent.
The A horizon is 10YR 6/3, 6/4, 7/2, 7/3, 7.5YR 6/2, 5/4, 6/4, 7/4. Moist color is 10YR 3/3, 3/4, 5/3, 5/4, 7.5YR 3/4, 4/4, 5/4, 5YR 4/4. Dry color in the surface 1 to 2 inches in some pedons is 10YR 5/2, 5/3, 7.5YR 5/2, and moist color is 10YR 3/2, 4/2, 7.5YR 3/2, 4/2. Texture is coarse sandy loam, sandy loam or loam with 10 to 25 percent clay. Content of coarse fragments is 0 to 35 percent with 0 to 5 percent cobbles. Reaction is very strongly acid to slightly acid.
The E horizon is 10YR 7/2, 7/3, 7.5YR 7/2; or 5YR 7/3. Moist color is 10YR 5/4, 6/4; 7.5YR 5/2; or 5YR 5/3. Texture is sandy clay loam, sandy clay or clay. Reaction is extremely acid to very strongly acid.
The 2Bt horizon is variegated with 2 to 4 or more colors in each subhorizon. The upper subhorizons are the most red. Pedons in swale areas generally are less red. Dominant color has hue of 10R through 10YR; value of 5, 6 or 7 dry and 4, 5 or 6 moist; and chroma of 4, 6 or 8 dry or moist. The minor color has hue of 10YR through 5Y or neutral; value of 7 or 8 dry or moist; and chroma of 0, 1 or 2 dry or moist. Texture is clay, sandy clay or silty clay with 40 to 70 percent clay. Clay content decreases with depth. Content of unrelated gravel that has moved down into cracks from the horizons above is 0 to 5 percent. Reaction is extremely acid to very strongly acid.
The 2BCt horizon is variegated with 2 to 4 or more colors. Individual colors are similar to the 2Bt horizon. Dominant color has hue of 10YR through 5Y or neutral; value of 7 or 8 dry or moist; and chroma of 0, 1 or 2 dry or moist. The minor color has hue of 10R through 10YR; value of 5, 6 or 7 dry and 4, 5 or 6 moist; and chroma of 4, 6 or 8 dry or moist. Texture is clay, sandy clay, or sandy clay loam with 27 to 55 percent clay. Reaction is extremely acid to very strongly acid.
The 2Cr horizon is variegated with 2 to 4 or more colors in the upper part but becomes more uniform with depth. Dominant color is 2.5YR 7/2, 8/2; 5Y 8/1, 8/2, or N 8/0. Moist color is 10YR 7/1; 2.5Y 7/2; 5Y 7/1, 6/3; or N 7/0. Minor colors include any color described in the 2Bt horizons. Reaction is extremely acid to very strongly acid.
COMPETING SERIES: There are no other soils in the family.
GEOGRAPHIC SETTING: The Mokelumne soils are on dissected terraces, hills, sideslopes of terrace remnants and in swales at elevations of 160 to 500 feet. Slopes are 2 to 35 percent. The soils formed in hillslope alluvium underalin by material weathered from sandstone or weakly consolidated clayey marine sediments of the Ione Formation. Coarse fragments in the material above the claypan contain dark metamorphic and quartzitic rocks. Climate is subhumid, with hot dry summers and cool, moist winters. Mean annual precipitation is 19 to 25 inches. Mean annual temperature is about 61 degrees F, average January temperature is 45 degrees F and average July temperature is 78 degrees F. The frost-free season is 250 to 275 days.
GEOGRAPHICALLY ASSOCIATED SOILS: These are Amador, Auburn, Creviscreek (T) and Vleck soils. Amador soils have a paralithic contact at a depth of 10 to 20 inches and are on foothills. Auburn soils have a lithic contact at a depth of 10 to 28 inches and are on foothills. Creviscreek soils have a fine-loamy textural control section and are on stream terraces. Vleck soils have a duripan and are on footslopes of hills.
DRAINAGE AND PERMEABILITY: Well drained, or moderately well drained in swales; medium to rapid runoff; very slow permeability.
USE AND VEGETATION: Used for annual rangeland and grazed woodland. A few areas are used for mining clay. Native vegetation consists of dense stands of live oak, blue oak, digger pine, manzanita, annual grasses and forbs. Chamise, deer vetch, live oak and annual grasses are common in areas with a coarse sandy loam surface texture. Various amounts of trees and brush have been cleared from many areas.
DISTRIBUTION AND EXTENT: Dissected terraces and hills along the western edge of the foothills of the Sierra Nevada Mountains. This series is of small extent.
MLRA SOIL SURVEY REGIONAL OFFICE (MO) RESPONSIBLE: Davis, California
SERIES ESTABLISHED: Amador County, Amador area, California, 1963.
REMARKS: This is a new typical pedon and is located in Sacramento County. The original pedon in Amador County was nongravelly. Only 208 acres of the nongravelly phase have been mapped. Diagnostic horizons and features recognized in this pedon are:
Ochric epipedon - the zone from the surface to 10 inches (A1, A2 horizons).
Argillic horizon - the zone from 10 to 39 inches (2Bt1, 2Bt2, 2Bt3, 2BCt horizons). Base saturation ranges from 15 to 35 percent throughout.
Typic Haploxerults feature - clay content decreases by 28 percent of the maximum above the Cr horizon.
Paralithic contact - 39 inches (2Cr)
ADDITIONAL DATA: Complete characterization data available for horizon 2Bt2, 12 to 20 inches (sampled as S83CA-067-13-3, 25 to 50 cm, 10 to 20 inches, 2Bt1); NSSL ID No. 84P0142.