LOCATION MALLOPASS CAEstablished Series
TAXONOMIC CLASS: Fine-loamy, mixed, superactive, isomesic Pachic Argiustolls
TYPICAL PEDON: Mallopass loam - on a northwest facing slope of 3 percent under annual grasses and forbs at 270 feet elevation. (Colors are for dry soil unless otherwise noted. When described on October 15, 1986, the soil was slightly moist throughout.)
A1--0 to 3 inches; very dark grayish brown (10YR 3/2) loam, black (10YR 2/1) moist; moderate medium and coarse granular structure; slightly hard, friable, slightly sticky and slightly plastic; many very fine and fine roots; many very fine tubular and interstitial pores; 5 percent hard angular sandstone pebbles (2- 20mm); moderately acid (pH 5.8); clear wavy boundary. (2 to 6 inches thick)
A2--3 to 14 inches; very dark grayish brown (10YR 3/2) loam, black (10YR 2/1) moist; strong medium, coarse and very coarse granular structure; slightly hard, friable, slightly sticky and slightly plastic; many very fine roots; many very fine tubular and interstitial pores; 5 percent hard angular sandstone pebbles (2- 20mm); moderately acid (pH 5.8); clear wavy boundary. (9 to 14 inches thick)
AB--14 to 23 inches; very dark gray (10YR 3/1) clay loam, black (10YR 2/1) moist; strong fine and medium subangular blocky structure; slightly hard, friable, slightly sticky and slightly plastic; common very fine roots; many very fine tubular and interstitial pores; 5 percent hard angular sandstone pebbles (2- 20mm); slightly acid (pH 6.5); gradual wavy boundary. (7 to 12 inches thick)
Bt1--23 to 34 inches; very dark grayish brown (10YR 3/2) clay loam, black (10YR 2/1) moist; strong fine and medium subangular blocky structure; slightly hard, friable, sticky and plastic; few very fine roots; many very fine tubular and interstitial pores; few thin and moderately thick clay films lining pores; 10 percent hard angular sandstone pebbles (2-40mm); neutral (pH 6.8); gradual wavy boundary. (9 to 14 inches thick)
Bt2--34 to 51 inches; light brownish gray (10YR 6/2) gravelly sandy clay loam, dark brown (10YR 3/3) moist; moderate fine and medium subangular blocky structure; hard, friable, slightly sticky and slightly plastic; few very fine roots; common very fine tubular and interstitial pores; few thin clay films on faces of peds and lining pores; 30 percent hard angular sandstone pebbles (2-50mm); neutral (pH 7.0); gradual wavy boundary. (10 to 18 inches thick)
Bt3--51 to 62 inches; light brownish gray (10YR 6/2) gravelly sandy clay loam, dark yellowish brown (10YR 4/4) moist; common fine and medium prominent strong brown (7.5YR 5/6) mottles, strong brown (7.5YR 5/8) moist; moderate fine and medium subangular blocky structure; hard, friable, slightly sticky and slightly plastic; few very fine roots; common very fine tubular and interstitial pores; few thin clay films on faces of peds and lining pores; 25 percent hard subangular, subrounded and rounded sandstone pebbles (2- 30mm); neutral (pH 7.0).
TYPE LOCATION: Mendocino County California; about 1775 feet south and 1850 feet west of the northeast corner of sec. 24, T.14N., R.17W., MDBM, Mallo Pass Creek quadrangle.
RANGE IN CHARACTERISTICS: Thickness of the solum and depth to bedrock is greater than 60 inches. Thickness of the mollic epipedon is 20 to 50 inches. The epipedon ranges from 0.6 to 4 percent organic carbon, decreasing regularly with increasing depth. The mean annual soil temperature ranges from 50 to 56 degrees F. The difference between mean summer and mean winter soil temperature ranges from 6 to 9 degrees F. The soil between the depths of 6 and 17 inches is moist in all parts from November 1 to June 1. It is dry in some or all parts from July 1 to October 1 in most years. The particle-size control section averages 25 to 30 percent clay.
The A horizon is 10YR 3/1, 3/2, 3/3, 4/l or 4/2. Moist color is 10YR 2/1, 2/2, 3/1 or 3/3. Clay content is 20 to 27 percent. Hard angular gravel content is 2 to 15 percent. Base saturation (ammonium acetate) ranges from 65 to 100 percent. Reaction is moderately or slightly acid.
The B horizon is 10YR 3/1, 3/2, 4/2, 4/3, 5/2, 5/3, 5/4, 6/2, 6/3, 7/2 or 7/3. Moist color is 10YR 2/1, 3/l, 3/2, 3/3, 4/2, 4/3, 4/4, or 4/6. Mottles are 7.5YR 5/6, 5/8; 10YR 5/6 or 5/8. Moist mottle color is 7.5YR 4/6, 5/6, 5/8, 10YR 5/4, 5/6, 5/8, 6/6 or 6/8. Mottles occur between 50 and 60 inches. The upper part of the B horizon is loam, clay loam, or sandy clay loam. The lower part is gravelly loam, gravelly clay loam or gravelly sandy clay loam. Clay content ranges from 25 to 35 percent. Gravel content ranges from 2 to 35 percent. Base saturation (ammonium acetate) ranges from 75 to 100 percent. Reaction is slightly acid or neutral.
COMPETING SERIES: These are the Abalobadiah (CA), Bruhel (CA), Candlestick (CA) and Miramar (CA) series. The Abalobadiah and Miramar soils are moderately deep to a paralithic contact. The Bruhel series has a solum less than 60 inches deep, lacks mottling and is well drained. The Candlestick series is moderately deep to a lithic contact.
GEOGRAPHIC SETTING: The Mallopass soils occur on coastal fan terraces. Slopes are 0 to 30 percent. Elevations are 50 to 800 feet. The soil formed in alluvium from mixed rock sources. The climate is humid with cool foggy summers and cool moist winters. A strong marine influence limits the diurnal and annual range of temperature. Mean annual precipitation ranges from 35 to 45 inches. Mean January temperature is about 48 degrees F. Mean July temperature is about 57 degrees F., and the mean annual temperature is 53 degrees F. The frost-free season is 250 to 330 days.
GEOGRAPHICALLY ASSOCIATED SOILS: These are the Biaggi, Bruhel, Cabrillo, Crispin, Flumeville and Windyhollow soils, all of which are on similar landscape positions. Biaggi soils lack mottling, are well drained and are moderately deep to a lithic contact. Cabrillo soils have mottles between 30 and 50 inches, are somewhat poorly drained and have loamy sand umbric epipedons. Crispin soils lack mottling, are well drained and are moderately deep to a cemented pan. Flumeville and Windyhollow soils are often in subtle depressions. Flumeville soils have mottles between 10 and 30 inches, are poorly drained and have a clayey particle-size class. Windyhollow soils have mottles between 30 and 50 inches and are somewhat poorly drained.
DRAINAGE AND PERMEABILITY: Moderately well drained. The soil is saturated with water for brief periods following episodes of heavy rain from December through April. The saturated zone starts at a depth of 48 inches and extends to greater than 60 inches. Surface runoff under bare soil conditions is very slow through rapid. Permeability is moderately slow.
USE AND VEGETATION: The soil is used for livestock grazing and as wildlife habitat. A few areas are used for hay and vegetable production and for homesites. Vegetation consists of perennial and annual grasses and forbs.
DISTRIBUTION AND EXTENT: Northern coastal California. The series is not extensive. MLRA 4.
MLRA SOIL SURVEY REGIONAL OFFICE (MO) RESPONSIBLE: Davis, California
SERIES ESTABLISHED: Mendocino County, California, Western part, 199388.
REMARKS: Diagnostic horizons and features recognized:
Mollic Epipedon (pachic) - 0 to 34 inches. (A1, A2, AB, Bt1).
Argillic horizon - 23 to 62 inches (Bt1, Bt2, Bt3)
Particle-size control section - 23 to 43 inches. Weighted average is 30 percent.
Many areas now mapped as the Mallopass series were mapped as Noyo clay loam, dark variant in the Soil Survey of the Mendocino County Bottomlands, California, 1973.
The activity class was added to the classification in February of 2003. Competing series were not checked at that time. - ET