LOCATION SECCA CAEstablished Series
TAXONOMIC CLASS: Fine, mixed, superactive, mesic Mollic Haploxeralfs
TYPICAL PEDON: Secca gravelly silt loam - native shrubs. (Colors are for dry soil unless otherwise noted.)
1 to 0 inches; gravel pavement.
A1--0 to 6 inches; brown (7.5YR 5/4) gravelly silt loam, dark reddish brown (5YR 3/4) moist; strong fine medium and coarse subangular blocky structure; slightly hard, friable, slightly sticky, plastic; many very fine and few fine roots; common very fine tubular and interstitial pores; a few cobblestones and about 40 percent gravel; moderately acid (pH 6.0); clear wavy boundary. (4 to 7 inches thick)
A3--6 to 15 inches; reddish brown (5YR 5/4) gravelly silt loam, dark reddish brown (5YR 3/4) moist; moderate medium and coarse subangular blocky structure; slightly hard, friable, sticky, plastic; few fine and common very fine, medium and coarse roots; common very fine tubular and interstitial pores; few thin clay films on peds and lining pores; a few cobblestones and about 25 percent gravel; slightly acid (pH 6.3); clear wavy boundary. (5 to 10 inches thick)
B1t--15 to 22 inches; yellowish red (5YR 5/6) cobbly silty clay loam, dark reddish brown (5YR 3/4) moist; moderate medium and coarse subangular blocky structure; hard, friable, sticky, plastic; few fine and common very fine, medium and coarse roots; many fine interstitial pores; common thin clay films on faces of peds and lining pores; some cobblestones and about 10 percent gravel; stone line in lower part; slightly acid (pH 6.5); abrupt wavy boundary. (3 to 8 inches thick)
B2t--22 to 36 inches; strong brown (7.5YR 5/6) cobbly clay, brown (7.5YR 4/4) moist; moderate coarse prismatic structure; extremely hard, very firm. very sticky, very plastic; few very fine and fine roots; few very fine tubular and interstitial pores; continuous moderately thick clay films on faces peds; common pressure faces and few fine manganese shot; neutral (pH 7.0); clear wavy boundary. (10 to 28 inches thick)
B3t--36 to 45 inches; light yellowish brown (2.5Y 6/4) light clay, yellowish brown (10YR 5/6) moist; weak coarse angular blocky structure; very hard, firm, very sticky, plastic; few very fine and fine roots; few very fine tubular and interstitial pores; many moderately thick clay films on faces of peds and lining pores; slightly alkaline (pH 7.5); gradual wavy boundary. (8 to 22 inches thick)
C--45 to 57 inches; weathered metabasic rock.
TYPE LOCATION: Nevada County, California; 5 miles SSW of Grass Valley; 1,300 feet east and 500 feet north of the west 1/4 corner of sec. 16, T.15N., R.8E.
RANGE IN CHARACTERISTICS: Depth to a paralithic contact and thickness of solum are 40 to 80 inches. The mean annual soil temperature at a depth of 20 inches is 56 degrees to 58 degrees F. The soil between the depths of about 5 to 15 inches is dry by late May or early June and remains dry until sometime in October. Otherwise, it is moist all of the time. Coarse fragments comprise up to 45 percent of the profile with the highest amount being in the A horizon and the B3t or C horizons. The upper 20 inches of the argillic horizon has from 2 to 30 percent coarse fragments by volume.
The A horizon is brown or reddish brown in hue of 7.5YR or 5YR. Moist chroma is 3 or 4 above 7 inches and 4 below 7 inches. The A horizon is loam, silt loam, or clay loam. It is slightly acid or medium acid. It has 2 to 4 percent organic matter in the upper 4 to 7 inches and less than 1 percent below 10 inches. The lower boundary of the A horizon is gradual or there is a transitional horizon between the A1 and B2t horizons.
The B2t horizon is reddish brown, yellowish red, reddish yellow, dark brown or strong brown in 5YR or 7.5YR hue and chroma is 4 or more. It is clay, and the average clay content is 35 to 60 percent except in the upper few inches. It ranges from slightly acid to slightly alkaline and usually increases with depth. It has 75 to 100 percent base saturation.
COMPETING SERIES: These are the Argonaut, Dearyton, Dubakella, Trabuco and Yorkville soils. Argonaut soils are 20 to 40 inches deep to weathered rock. Dearyton and Yorkville soils have no hues redder than 10YR. Dubakella soils are 20 to 40 inches to hard rock and have more than 35 percent coarse fragments. Trabuco soils have a mean annual soil temperature above 59 degrees F.
GEOGRAPHIC SETTING: Secca soils occur on gently sloping to steep mountainous terrain at elevations between 1,700 and 3,000 feet. The underlying bedrock consists of metabasic, basic and ultrabasic volcanic rock. The climate is moist subhumid mesothermal with warm dry summers and cool moist winters. Mean annual precipitation is 35 to 55 inches, some of which falls as snow. Mean annual temperature is about 56 degrees F.; average January temperature is about 43 degrees F.; average July temperature is about 75 degrees F.
GEOGRAPHICALLY ASSOCIATED SOILS: These are the Auburn, Boomer, and Sites soils, and the competing Argonaut and Dubakella soils. Auburn soils have a lithic contact above 20 inches in part of each pedon. Boomer soils have less than 35 percent clay in the argillic horizon. Sites soils have a base saturation of less than 35 percent in the argillic horizon.
DRAINAGE AND PERMEABILITY: Moderately well-drained; slow to rapid runoff; slow permeability.
USE AND VEGETATION: Limited grazing and watershed use. Vegetation is manzanita, ceanothus, blue oak, grasses and forbs with scattered digger pine and occasional ponderosa pine.
DISTRIBUTION AND EXTENT: The middle mountain areas of the central Sierra Nevada in California. The series is of moderate extent.
MLRA SOIL SURVEY REGIONAL OFFICE (MO) RESPONSIBLE: Davis, California
SERIES ESTABLISHED: Nevada County Area, California, 1970.
REMARKS: The Secca soils would formerly have been classified as Reddish Brown Lateritic soils.
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 3/71.