Established Series


The Whiterock series consists of very shallow and shallow, somewhat excessively drained soils formed in residuum weathered from metasedimentary rocks. Whiterock soils are on hills. Slopes are 3 to 60 percent. The mean annual precipitation is about 590 mm and the mean annual air temperature is about 16 degrees C.

TAXONOMIC CLASS: Loamy, mixed, superactive, nonacid, thermic Lithic Xerorthents

TYPICAL PEDON: Whiterock loam on a southwest facing, 7 percent, convex slope under annual grasses and forbs at an elevation of 119 meters. (Colors are for dry soil unless otherwise stated. When described September 28, 1982, the soil was moist throughout.)

A1--0 to 3 cm; pale brown (10YR 6/3) loam, brown (10YR 4/3) moist, weak fine platy structure, slightly hard, friable, nonsticky, and nonplastic; many fine and common very fine roots; common very fine interstitial and common very fine and fine tubular pores; 0.5 cm thick mat of decomposed litter at surface; 10 percent angular gravel, strongly acid (pH 5.2); abrupt smooth boundary. (3 to 8 cm thick)

A2--3 to 20 cm; very pale brown (10YR 7/3) loam, brown (10YR 4/3) moist; structureless massive; slightly hard, friable, slightly sticky and nonplastic; common very fine roots; few very fine interstitial and common very fine tubular pores; 10 percent angular gravel, moderately acid (pH 5.9); abrupt irregular boundary. (8 to 28 cm thick)

R--20 to 30 cm; highly fractured and vertically tilted metasedimentary rock; common very fine roots between fractures, fractures 1 to 4 cm apart.

TYPE LOCATION: Sacramento County, California; about 6.9 km (4.3 mi) southwest of Clarksville, 4 km (2.5 mi) west of Malby Crossing, 457 meters (1,500 feet) west of the junction of Whiterock Road and Scott Road, 183 meters (600 feet) north of Whiterock Road, 3,550 feet north and 1,500 feet west of the southeast corner of section 20, T.9 N., R.8 E. USGS 7.5 minute topographic quadrangle: Clarksville, California; WGS84 38.6272240 latitude and -121.0958328 longitude. UTM Zone 10 665754 meters E 4277130 meters N NAD83.


Soil temperature: The mean annual soil temperature at the lithic contact is 17 to 19 degrees C and remains above 8 degrees C throughout the year. The difference between the mean summer and mean winter soil temperature is greater than 6 degrees C. The soils have a thermic temperature regime

Soil moisture: The soil moisture control section is dry in all parts from about May to October. The soils have a xeric moisture regime.

Diagnostic features:
Ochric epipedon thickness: 2 to 18 cm
Depth to lithic contact: 10 to 35 cm

Particle size control section weighted averages:
Clay content: 12 to 25 percent
Rock fragments: 5 to 35 percent

Base saturation (by ammonium acetate) is 60 to 80 percent throughout

Organic matter content: 2 to 6 percent in the upper 1 to 4 cm. Less than 2 percent below this depth.

A horizons (A1 and A2)
Hue: 2.5Y, 10YR
Value: 6 to 8 dry; 4 or 5 moist
Chroma: 2 to 4 dry; 2 or 3 moist
Texture: silt loam or loam
Rock fragments: 5 to 35 percent
Clay content: 12 to 25 percent
Sand content: 25 to 50 percent
Reaction: strongly acid or moderately acid

R horizon
Hue: 5Y, 2.5Y, 10YR
Value: 3 to 6
Chroma: 2 or 3

COMPETING SERIES: These are the Daulton, Exchequer, Gaviota, Goldwall, Ocraig, and Snook (MLRA 5) soils. Daulton and Exchequer soils have an epipedon with a dry value of 3 to 5 in all parts. Exchequer soils also have moist chromas of 4 to 8. Gaviota soils have greater than 50 percent sand and a lithic contact that lacks fractures. Goldwall soils are less than 25 cm to indurated volcanic bedrock. Ocraig soils have a coarse plus very coarse sand content of greater than 20 percent. Snook soils have mean annual soil temperatures of 15 to 17 degrees C.

GEOGRAPHIC SETTING: The Whiterock soils are on backslopes of hills at elevations of 50 to 760 meters. Slopes are 3 to 60 percent. The soils formed in residuum weathered from slate, schist, and partially metamorphosed sandstone. These metasedimentary rocks of the Mariposa Formation are nearly vertically tilted and slab like rock outcrops are common. The climate is subhumid with hot dry summers and cool, moist winters. Mean annual precipitation is 400 to 760 mm. Mean annual air temperature is about 16 to 17 degrees C; average January air temperature is about 7 to 8 degrees C and average July air temperature is about 25 to 26 degrees C. The frost-free period is 260 to 350 days.

GEOGRAPHICALLY ASSOCIATED SOILS: These are the competing Daulton and Exchequer soils and the Amador, Argonaut, Auburn, Copperopolis, and Hornitos soils. Daulton and Exchequer occupy similar landform positions, but Daulton soils form in dark colored slates and Exchequer soils form in metavolcanic rock. Amador soils form on hills from rhyolite or acidic tuff, and are less than 50 cm to a paralithic contact. Argonaut soils form on concave positions on hills from metavolcanic rock, have an argillic horizon, and a paralithic contact from 50 to 100 cm. Auburn soils form on hills from metavolcanic rock and have a cambic horizon. Copperopolis soils form on the summit of hills, have greater than 35 percent rock fragments in the particle size control section, and have a cambic horizon. Hornitos soils form on hills from sandstone and have a cambic horizon.

DRAINAGE AND PERMEABILITY: Somewhat excessively drained, moderately high to high saturated hydraulic conductivity throughout the soil. Saturated hydraulic conductivity of the bedrock is low to very high.

USE AND VEGETATION: These soils are primarily used for rangeland. Native vegetation consists of scattered blue oaks with an understory of grasses and forbs including bromes, bedstraw, soft chess, foxtail fescue, wild oat and filaree.

DISTRIBUTION AND EXTENT: Sierra Nevada Foothills of California; MLRA 18. The series is moderately extensive.


SERIES ESTABLISHED: Sacramento County, California, 1946. Source of the name is from the community of White Rock, CA.

Diagnostic horizons and features recognized in this pedon are:
Ochric epipedon: 0 to 20 cm (A1 and A2 horizon)
Lithic contact: 20 to 30 cm (R horizon) vertically tilted fractures are 1-4 cm apart. Fragments of rock do not slake in water.
Particle size control section for this pedon: 0 to 20 cm

This new typical pedon is within a mile of the original type location. The Whiterock soils were formerly classified as loamy, mixed, acid, thermic Lithic Xerorthents. Data from published soil survey reports and from the new type location do not support the former classification.

Type location should be examined to determine presence of C horizon over the R and consequently, depth class. The 1-4 cm fractures with roots in the bedrock horizon suggest that this horizon is not a lithic contact.

NASIS User Pedon ID: 82CA067003
Pedon Purpose: laboratory sample site
Lab Pedon #: 83P0293
Lab Source ID: SSL

Soil classified using the 12th Edition of the Keys to Soil Taxonomy.

National Cooperative Soil Survey