Established Series


The Rocklin series consists of moderately deep to hardpan, well or moderately well drained soils that formed in old alluvium from granitic rock sources. They are on nearly level to rolling dissected terraces and have slopes of 0 to 15 percent. The mean annual precipitation is about 15 inches and the mean annual temperature is about 61 degrees F.

TAXONOMIC CLASS: Fine-loamy, mixed, superactive, thermic Typic Durixeralfs

TYPICAL PEDON: Rocklin fine sandy loam on a less then 3 percent slope under annual grasses and forbs at 200 feet elevation. (Colors are for dry soil unless otherwise stated.)

A--0 to 8 inches; light brown (7.5YR 6/4) fine sandy loam, dark brown (7.5YR 4/4) moist; massive; hard, very friable, slightly sticky and slightly plastic; very fine roots; many fine tubular pores; slightly acid (pH 6.1); clear smooth boundary. (6 to 12 inches thick)

Bt--8 to 24 inches; yellowish red (5YR 5/6) loam, yellowish red (5YR 4/6) moist; moderate fine subangular blocky structure; hard, friable, sticky and plastic; common very fine roots; fine tubular pores; common thin nearly continuous clay films on ped faces; slightly acid (pH 6.2); abrupt smooth boundary. (10 to 18 inches thick)

Bqm--24 to 28 inches; reddish yellow (5YR 6/8) indurated duripan; extremely hard, brittle; neutral (pH 6.8); clear wavy boundary. (4 to 12 inches thick)

BCq--28 to 60 inches; reddish yellow (5YR 6/6 and 6/8) weakly cemented stratified sediments that crush to fine sandy loam, yellowish red (5YR 5/6 and 5/8) moist; massive; very hard and dense, brittle, nonsticky and nonplastic; neutral (pH 6.8); strongly cemented to indurated laminar bands are present in vertical cracks deep into the substratum in a very coarse polygonal or prismatic pattern.

TYPE LOCATION: Merced County, California, 1/4 mile south of NW corner. sec. 22, T. 5 S., R. 12 E.

RANGE IN CHARACTERISTICS: Depth to the duripan ranges from 20 to 40 inches. A dense weakly cemented layer immediately underlies the duripan. It has more than 15 percent coarse plus very coarse sand. The soil temperature is not below 47 degrees F. at any time. The soil, at depth of 7 to 24 inches or the duripan, is dry in all parts from June to November unless irrigated and is moist in some or all parts the rest of the year.

The A horizon has dry color of 5YR 6/4, 5/4; 7.5YR 6/4, 5/6, 5/4; 10YR 6/3, 5/3 or 5/2. Moist color is 5YR 3/4; 7.5YR 4/4, 3/4; 10YR 4/3 or 3/3. Texture is fine sandy loam, sandy loam or loam with 10 to 25 percent clay. Reaction is moderately acid to slightly acid.

The BAt horizon when present has dry color of 5YR 6/3; 7.5YR 6/4, 5/4; or 10YR 5/3. Moist color is 5YR 4/4, 3/4; 7.5YR 4/4, 3/4; or 10YR 3/4. Texture is fine sandy loam or sandy loam with slightly more clay than the A horizon. Reaction is slightly acid to neutral.

The Bt horizon has dry color of 5YR 5/6, 5/4, 4/4; 7.5YR 6/4, 5/4, 4/6 or 4/4. Moist color is 5YR 4/6, 4/4, 3/4; 7.5YR 4/4, 3/4; or 2.5YR 3/4. Texture is loam, sandy clay loam or clay loam with 18 to 30 percent clay, but averaging less than 27 percent clay in the argillic horizon. Some pedons may contain up to 5 percent gravel. Reaction is slightly acid to neutral.

The Bqm horizon has dry color of 5YR 6/8, 6/6, 5/6, 5/4, 4/4; 7.5YR 6/6 or 6/4. Moist color is 5YR 5/4, 4/6, 4/4, 3/4; or 7.5YR 4/4. It is strongly cemented to indurated. This hardpan may be irregularly interrupted by weakly cemented material or occasionally may be absent with "windows" filled with coarse textured material.

The BCq horizon has similar color and reaction as the Bqm horizons. The weak silica cementation is dense and brittle, but not a duripan, and crushes to a sandy loam, coarse sandy loam or fine sandy loam.

COMPETING SERIES: These are the Buchenau, Exeter, Fiddyment and Monserate series. Buchenau soils are calcareous throughout and have variable amounts of salt and sodium. Exeter soils lack any cementation below the thin duripan and lack moderately developed subangular blocky Bt horizons. Fiddyment and Monserate soils average 27 to 35 percent clay in the argillic horizon.

GEOGRAPHIC SETTING: The Rocklin soils are on nearly level to rolling dissected terraces at elevations of 80 to 500 feet in the Central Valley and about 2500 feet or less in the intermountain valleys. Slopes are 0 to 15 percent. The soils formed in old alluvium from granitic rock sources. The climate is subhumid with hot, dry summers and cool, moist winters. Mean annual precipitation is 10 to 20 inches. Mean January temperature is 45 to 48 degrees F; mean July temperature is 78 to 82 degrees F. The mean annual temperature is 60 to 62 degrees F. Frost-free period is 230 to 300 days.

GEOGRAPHICALLY ASSOCIATED SOILS: These are the Cometa and San Joaquin soils and the competing Exeter soils. Cometa and San Joaquin soils have fine textured argillic horizons.

DRAINAGE AND PERMEABILITY: Well drained; very slow to medium runoff; moderate permeability above cemented material but very slow to slow below.

USE AND VEGETATION: The soil is used for livestock grazing and nonirrigated small grain crops. Some areas are used for irrigated pasture and vineyards. Vegetation is annual grasses and forbs such as soft chess, oats and filaree with a few scattered oaks.

DISTRIBUTION AND EXTENT: Eastern edge of San Joaquin and intermountain valleys of southern California. The soils are moderately extensive in MLRA-17.


SERIES ESTABLISHED: Auburn Area, Placer County, California, 1924. (Source of name is town of Rocklin, Placer County.)

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

Diagnostic horizons and features recognized in this pedon are:

Ochric epipedon - the zone from the surface to a depth of 8 inches (A)

Argillic horizon - the zone from 8 to 24 inches (Bt)

Duripan - the zone from 24 to 28 inches (Bqm)

Cemented underlying layers - the zone from 28 to 60 inches (BCq)

National Cooperative Soil Survey