LOCATION USAL CAEstablished Series
TAXONOMIC CLASS: Fine-loamy, mixed, superactive, isomesic Typic Argiudolls
TYPICAL PEDON: Usal gravelly loam on a west facing convex slope of 65 percent under Douglas-fir, grand fir, redwood and swordfern at 195 meters (640 feet) elevation. (Colors are for dry soil unless otherwise stated. When described on November 8, 1979 the soil was moist throughout).
Oi--0 to 5 centimeters (0 to 2 inches); litter of Douglas-fir, grand fir and redwood; 5 percent gravel (2-30millimeters).
A--5 to 41 centimeters (2 to 16 inches); brown (10YR 5/3) gravelly loam, dark brown (10YR 3/3) moist; strong fine and medium granular structure; slightly hard, very friable, slightly sticky and slightly plastic; few fine and medium and many very fine roots; common medium and many fine and very fine interstitial and common very fine tubular pores; 25 percent gravel (2-25 millimeters); neutral (pH 7.0); clear wavy boundary. (25 to 46 centimeters thick)
Bt1--41 to 58 centimeters (16 to 23 inches); variegated light yellowish brown and very pale brown (10YR 6/4, 7/4) gravelly clay loam, dark yellowish brown and yellowish brown (10YR 4/4, 5/4) moist; strong fine and medium subangular blocky structure; hard, friable, slightly sticky and slightly plastic; common medium and coarse and few very fine and fine roots; few fine and common very fine interstitial and few very fine tubular pores; many faint clay films on peds and in pores; 15 percent gravel (2-25 millimeters); slightly acid (pH 6.5); gradual wavy boundary. (15 to 23 centimeters thick)
Bt2--58 to 79 centimeters (23 to 31 inches); very pale brown (10YR 7/4) gravelly clay loam, yellowish brown (10YR 5/6) moist; strong fine and medium angular blocky structure; hard, friable, sticky and plastic; few fine and common medium and coarse roots; few very fine and fine interstitial pores; many distinct clay films on peds and in pores; 15 percent gravel (2-25millimeters); slightly acid (pH 6.5); gradual irregular boundary. (10 to 25 centimeters thick)
Bt3--79 to 89 centimeters (31 to 35 inches); light yellowish brown (10YR 6/4) very gravelly clay loam, yellowish brown (10YR 5/4) moist; moderate fine and medium angular blocky structure; hard, friable, slightly sticky and slightly plastic; few fine and medium roots; few very fine and fine interstitial pores; many distinct clay films on peds; 45 percent gravel (2-50millimeters); slightly acid (pH 6.5); abrupt irregular boundary. (0 to 10 centimeters thick)
C--89 to 200 centimeters (35 to 79 inches); gravel; hard, fractured fine grained sandstone and mudstone. Fractures are 0.5 to 1 centimeters apart and 1 to 2 millimeters wide.
TYPE LOCATION: Mendocino County, California; about 100 feet downhill of Georgia-Pacific road #11010 at a point on the saddle at the headwaters of Frazier Creek; about 2000 feet east and 2500 feet south of the northwest corner of sec. 27, T.20N., R.17W., U.S.G.S. Branscomb quadrangle.
RANGE IN CHARACTERISTICS:
Soil moisture: The soil between depths of 25 and 64 centimeters is moist in all parts from November 1 to August 1 and is dry in some part from September 1 to October 1 in most years.
Soil temperature: 11 to 13 degrees C. The difference between mean summer and mean winter temperature varies from 2 to 3 degrees C.
Depth to lithic material with fractures less than 10 centimeters apart: 50 to 99 centimeters (20 to 39 inches)
Particle size control section (weighted average):
Rock fragments: 15 to 35 percent
Clay content: 25 to 35 percent
Reaction: slightly acid or neutral
Base saturation (sum): ranges from 75 to 90 percent throughout
A horizon:
Hue: 10YR
Value: 4 or 5 dry, 2 or 3 moist
Chroma: 2 or 3
Rock fragments: 5 to 25 percent
Clay content: 20 to 27 percent
Organic carbon content: 2 to 5 percent
Bt horizon:
Hue: 10YR
Value: 6 or 7 dry, 4 or 5 moist
Chroma: 3 or 4 dry, 3 through 6 moist
Rock fragments: 15 to 50 percent
Texture of fine earth: loam, clay loam
Clay content: 25 to 35 percent
C horizon:
Texture: gravel
COMPETING SERIES: There are no other series in the same family.
GEOGRAPHIC SETTING: Usal soils are on hill slopes adjacent to the Pacific coast. Slopes are 30 to 99 percent. The soils occupy a transitional position between the Mollisols on coastal grassland terraces to the west and the Ultisols and Alfisols on uplands to the east. Elevations are 3 to 245 meters (10 to 800 feet). The soils formed in material weathered from sandstone and mudstone. A strong marine influence limits the diurnal and annual ranges of temperature. The climate is humid with cool foggy summers and cool moist winters. Mean annual precipitation ranges from 1000 to 1500 millimeters (40 to 60 inches). Mean January temperature is 10 degrees C (50 degrees F); mean July temperature is 13 degrees C (55 degrees F), and the mean annual temperature is 12 degrees C (53 degrees F). The frost-free period is 290 to 365 days.
GEOGRAPHICALLY ASSOCIATED SOILS: These are the Dehaven, Hotel, Irmulco, and Tramway soils. All occur on hill slopes. Dehaven and Hotel soils formed from slightly harder sandstone and have loamy-skeletal particle-size control sections. Irmulco soils are greater than 100 centimeters deep to lithic material. Tramway soils lack a mollic epipedon.
DRAINAGE AND PERMEABILITY: Well drained; surface runoff under bare soil conditions is high or very high; moderate permeability.
USE AND VEGETATION: This soil is used for commercial timber production, and as wildlife habitat and watershed. Natural vegetation is grand fir, redwood, Douglas-fir, tanoak, swordfern, oxalis and Oregon grape.
DISTRIBUTION AND EXTENT: Northern coastal California. Soil occurs in the zone of strong marine influence. The series is not extensive.
MLRA SOIL SURVEY REGIONAL OFFICE (MO) RESPONSIBLE: Davis, California
SERIES ESTABLISHED: Mendocino County, California, 1952, State Cooperative Soil-Vegetation Survey, California Division of Forestry.
REMARKS: Diagnostic horizons and features recognized in this pedon are:
Mollic epipedon -- the zone from 5 to 41 centimeters (0 to 14 inches) (A horizon)
Argillic horizon -- the zone from 41 to 89 centimeters (14 to 21 inches) (Bt1, Bt2 and Bt3 horizons)
This is a change in classification from fine-loamy, mixed, isomesic Typic Humitropept to fine-loamy, mixed, isomesic Typic Argiudolls; and a change in type location.
The activity class was added to the classification in March of 2003. - ET
The depth class was changed to reflect the fracture spacing in the lithic material in February 2008. - ET.