Established Series


The Cometa series consists of moderately deep, moderately well or well drained soils that formed in alluvium from granitic rock sources. These soils are on gently sloping, slightly dissected older stream terraces and have slopes of 0 to 15 percent. The mean annual precipitation is about 16 inches and the mean annual air temperature is 62 degrees F.

TAXONOMIC CLASS: Fine, mixed, superactive, thermic Typic Palexeralfs

TYPICAL PEDON: Cometa sandy loam - rangeland. (Colors are for dry soil unless otherwise stated.)

A--0 to 7 inches; brown (10YR 5/3) sandy loam, dark brown (10YR 3/3) moist; massive; hard, friable, nonsticky and nonplastic; few fine tubular pores; slightly acid (pH 6.2); clear smooth boundary. (4 to 12 inches thick)

AB--7 to 17 inches; brown (7.5YR 5/4) sandy loam, brown (7.5YR 4/2) moist; massive; hard, friable, nonsticky and nonplastic; few fine tubular pores; slightly acid (pH 6.3); abrupt smooth boundary. (8 to 16 inches thick)

Bt--17 to 27 inches; reddish brown (5YR 4/4) sandy clay, dark reddish brown (5YR 3/4) moist; strong coarse angular blocky structure; extremely hard, firm, plastic and slightly sticky; few fine tubular pores; continuous moderately thick clay films on faces of peds; slightly acid (pH 6.4); abrupt smooth boundary. (8 to 18 inches thick)

C--27 to 60 inches; light yellowish brown (10YR 6/4) weakly stratified sandy loam, dark yellowish brown (10YR 4/4) moist; massive; hard, firm, nonsticky and nonplastic; weak stratification is visible; neutral (pH 7.2).

TYPE LOCATION: Madera County, California; NE 1/4, NE 1/4, sec. 17, T. 10 S., R. 19 E.

RANGE IN CHARACTERISTICS: The mean annual soil temperature is about 60 to 65 degrees F. The soil between depths of 8 and 20 inches is usually moist all of the time from November until late May or early June and is dry in some or all parts the rest of the year. The solum thickness ranges from 24 to 40 inches. Some pedons have dense, weakly cemented layers underlying the argillic horizon.

The A horizon is 10YR 5/2, 5/3, 6/3, 5/4; 7.5YR 5/2 or 5/4. Moist colors are 10YR 3/3, 4/3 or 7.5YR 4/2, 4/4. It is coarse sandy loam, sandy loam, fine sandy loam or loam. The A horizon is massive and hard when dry and has less than 1 percent organic matter. Reaction is slightly acid or moderately acid.

The Bt horizon is 7.5YR 4/2, 5/2, 4/4, 5/4, 4/6; 5YR 5/3, 4/3, 5/4, 4/4 or 4/6. Moist colors are 1 or 2 units of value darker. It is clay, sandy clay or clay loam. The silt plus very fine sand is less than 40 percent. Structure is strong angular blocky prismatic or columnar and when dry a thin layer of bleached sand grains is visible in some pedons as coatings capping columns. Reaction is slightly acid or neutral.

In some pedons a Btq horizon is below the argillic horizon. It has similar colors and reaction as C horizons and has clay films and weak silica cementation. The horizon is dense and brittle, but is not a duripan because it slakes in water after prolong soaking and crushes to a sandy loam or coarse sandy loam texture.

The C horizon is 7.5YR 4/4, 5/4, 5/6; 10YR 5/4, 6/4. Moist colors are 7.5YR 4/4, 5/4; 10YR 4/4, 5/4. They are compact, have high bulk density and are impermeable to moisture and roots. Texture is coarse sandy loam, sandy clay loam, sandy loam or fine sandy loam. The C horizon is weakly stratified.

COMPETING SERIES: These are the Hytop, Millsap, Orognen and Yokayo soils. Hytop and Millsap soils are 20 to 40 inches deep to bedrock. Orognen soils have a solum greater than 40 inches thick. Yokayo soils have 10YR and 2.5Y hue in the Bt horizon.

GEOGRAPHIC SETTING: The Cometa soils are on gently sloping and undulating, slightly dissected older stream terraces with slopes of 0 to 15 percent. They occur at elevations of 20 to 600 feet in a subhumid climate with mean annual rainfall of 10 to 23 inches, with hot, dry summers and cool, moist winters. Mean annual temperature is 58 to 64 degrees F, average January temperature is 44 degrees F, and average July temperature is 79 degrees F. The frost-free period is about 260 to 300 days.

GEOGRAPHICALLY ASSOCIATED SOILS: These are the Fiddyment, Rocklin, San Joaquin, Snelling and Whitney soils. Fiddyment, Rocklin and San Joaquin soils have duripans. Snelling and Whitney soils have fine-loamy argillic horizons.

DRAINAGE AND PERMEABILITY: Moderately well or well drained; slow to medium runoff; very slow permeability.

USE AND VEGETATION: Used for rice, vineyards, orchards, dry-farmed grain and livestock grazing. Vegetation consists of annual grasses, forbs and weeds.

DISTRIBUTION AND EXTENT: The soils occur on the east side of the lower Sacramento and San Joaquin Valleys and intermountain valleys of the central Coast Range. The soils are of moderate extent in MLRA-17.


SERIES ESTABLISHED: Stockton Area, Stanislaus County, California, 1939.

REMARKS: The soils were formerly classified as (maximal) Noncalcic Brown soils. The Stockton area soil survey includes San Joaquin, Stanislaus and Calaveras counties. The original type location was in Stanislaus County, but it was later moved to Madera County.

This update (12/87) correlate and correct the concept of the Cometa series as mapped in Eastern Fresno, Madera, San Benito, and Placer Counties (80,082 acres). The Cometa soils as mapped in Sutter County (11,785 acres) are excluded from the series concept. They should be mapped as as a different series because the solum thickness is greater than 60 inches.

The activity class was added to the classification in January of 2003.

Diagnostic horizons and features recognized in this pedon are:

Ochric epipedon - the zone from 0 to 17 inches (A, AB)

Argillic horizon - the zone from 17 to 27 inches (Bt)

National Cooperative Soil Survey