Established Series


The Modesto series consists of moderately well drained, (medial) Noncalcic Brown soils developed from alluvium derived largely from granitic rock sources but with some mixture from metamorphic rocks. They occur on nearly level alluvial fans in areas where the surface drainage is very slow. These soils are reported to have had a mound type of microrelief, but this has been almost completely destroyed by leveling. The soils are formed on rather gritty, sandy loam or loam textured alluvium underlain in many places by a silty substratum like that underlying the Dinuba and Hanford soils. The Modesto soils characteristically have neutral, grayish brown or dark grayish brown surface layers of loams and clay loams which become puddled and dense when cultivated in the moist condition. They have blocky to prismatic light clay or sandy clay B2 horizons which are mildly basic and intermittently calcareous in the lower part. The underlying material may be sandy alluvium or unrelated silty substrata, occasionally cemented with lime to form thin, weak hardpans.

TAXONOMIC CLASS: Fine-loamy, mixed, active, thermic Mollic Haploxeralfs

TYPICAL PEDON: Modesto loam (cultivated irrigated pasture)

Ap--0 to 10 inches; grayish brown (10YR 5/2) loam (somewhat gritty and puddled very dark grayish brown (10YR 3/1.5) moist; massive; very hard friable, slightly sticky and slightly plastic; few pores, numerous fine roots; moderately acid (pH 5.8); abrupt smooth boundary. 8 to 10 inches thick.

AB--10 to 12 inches; between grayish brown (10YR 5/2) and brown (10YR 5/3) light clay loam, very dark grayish brown (10YR 3/2.5) moist; moderate medium and coarse blocky structure; very hard, firm, plastic and slightly sticky; few fine pores, common fine roots; slightly acid (pH 6.1); this layer may have been somewhat mixed by leveling or cultivation.

B21--12 to 22 inches; brown (10YR 5/3) light clay; dark brown (10YR 3.5/3) moist with very dark brown (7.5YR 2.5/2) coatings; moderate coarse prismatic structure changing to strong coarse angular blocky in the lower part; very hard, firm, plastic and sticky; thick continuous clay films on all ped faces; common fine pores and fine roots; slightly acid (pH 6.3); clear smooth boundary. 10 to 13 inches thick.

B22--22 to 35 inches; brown (10YR 4.5/3) light clay, dark brown (10YR 3.5/3) moist with coatings of dark gray (7.5YR 4/1) dry, very dark brown (7.5YR 2/2) moist; similar to above but with few roots and with increasing pH (6.7); gradual smooth boundary. 8 to 12 inches thick.

B31--35 to 44 inches; brown (10YR 5/3) sandy clay loam, dark brown (7.5YR 312) moist; very weak coarse blocky structure; hard, friable, plastic and slightly sticky; thin clay films on vertical faces; neutral (pH 6.8); gradual smooth boundary. 6 to 12 inches thick.

B32--44 to 55 inches; brown (10YR 5/3) heavy sandy loam, dark brown (10YR 4/2.5) moist; massive; few thin patchy clay films; neutral (pH 6.8) abrupt irregular boundary. 6 to 12 inches thick.

D--55 to 62 inches +; light gray (2.5Y 7/2) silt loam, olive gray (2.5Y 5/2) moist with common medium distinct mottles of yellowish brown (10YR 5/6) dry, yellowish brown (10YR 3/6 to 5/6) moist; massive; hard, firm and somewhat brittle when moist, slightly plastic when crushed wet; neutral (pH 6.9); stratified with very fine sandy loam in places. Several feet thick.

TYPE LOCATION: Stanislaus County, California; 660 feet W. and 300 feet N. of east 1/4 corner of Sec. 17, T. 3S., R. 9E., 2 1/2 miles N. of Modesto, 1/8 mile west of McHenry Avenue, 100 yards north of Bowden Avenue.


A1 horizons vary in texture from loam to clay loam and in color from grayish brown (10YR 5/2) to gray (10YR 5/1) or dark grayish brown (10YR 4/2) and reaction from pH 6.0 to 7.0.

B2 horizons are brown (10YR 5/3, 7.5YR 5/3) or dark brown (10YR 4/3, 7.5YR 4/3) with slightly redder clay coatings on ped surfaces. Structure of the B2 horizon is moderate to strong coarse prismatic. The pH is always more alkaline in the B2 horizon than in the A horizon and is generally between 7.5 and 8.0 with some segregated lime in the lower part; however, the lime occurs only intermittently.

The underlying material is variable ranging from sandy loam to compact silt loam similar to that found under the Dinuba soils. Where the compact silt loam occurs at depths of 3 to 4 feet, it is often partially cemented with lime to a moderately dense hardpan. The silty material is devoid of coarse sand indicating that it is unrelated to the solum above which is usually somewhat gritty throughout. A few areas are affected by weak alkaline salts.


GEOGRAPHIC SETTING: Nearly level, slowly drained alluvial fans or interfan areas approaching basin topography, formerly with mound microrelief which is now largely destroyed by leveling for irrigation. Modesto soils occur at elevations of 40 to 100 feet in a mesothermal semiarid climate having a mean annual precipitation of 10 to 12 inches with hot dry summers and cool moist winters; an average temperature of 45 degrees F. in January, 78 degrees F. in July with a mean annual temperature of 60 degrees F. The average frost-free season is about 300 days.

GEOGRAPHICALLY ASSOCIATED SOILS: The Modesto soils are associated with the Chualar, Dinuba, and Hanford soils. They differ from Chualar soils in that they are generally finer textured, less permeable, have hard rather than soft consistence in the A horizon, and have more distinctly blocky or prismatic B2 horizons. Where they are underlain by silty substrata, they resemble the Dinuba soils which, however, have only weakly developed, sandy loam B2 horizons. The Merriam soils have brown or reddish brown A horizons which abruptly overlie prismatic clay or heavy sandy clay B2 horizons.

DRAINAGE AND PERMEABILITY: Soils are moderately well drained to somewhat poorly (imperfectly) drained with very slow surface runoff, locally ponded. The B2 horizon is slowly permeable and if puddled by cultivation the surface soil becomes very slowly permeable. Water tables are variable ranging from 3 to 10 feet, depending upon the proximity of artificial drains and drainage wells. Perched water often occur in wet years where the soil is underlain by the compact silt.

USE AND VEGETATION: Annual grasses and herbaceous plants; morning glory (bindweed), star thistle, and Johnson grass are troublesome weeds in places. These soils are used for growing grapes, orchard, field, and forage crops and irrigated pasture. Unless these soils are carefully managed the poor structure causes reduced yields.

DISTRIBUTION AND EXTENT: Eastern side of central San Joaquin valley, California.


SERIES ESTABLISHED: Modesto-Turlock Area, California, 1908. Source of name is city of Modesto, Stanislaus County.)

REMARKS: The activity class was added to the classification in January of 2003. Competing series were not checked at that time. - ET

OSED scanned by SSQA. Last revised by state on 1/6/59.

National Cooperative Soil Survey