Established Series


The Butano series consists of well drained, moderately permeable soils developed from weathered siliceous shales of the Monterey formation. They occur on sloping to steep topography under coniferous forests. Mean annual rainfall is 30 to 50 inches and mean annual temperature is about 52 degrees F.

TAXONOMIC CLASS: Fine-loamy, mixed, superactive, mesic Typic Hapludults

TYPICAL PEDON: Butano silt loam (virgin)

A00 & A0--2 to 0 inches; fresh and partly decomposed forest litter, consisting of needles, leaves, twigs and branches. Abrupt smooth lower boundary. (1/4 to 3 inches thick)

A1--0 to 3 inches; light brownish gray (10YR 6/2) silt loam, dark grayish brown, (10YR 4/2) when moist; moderate medium and fine granular structure; very hard when dry, friable when moist; numerous roots and insect and worm holes; low in organic matter; medium acid; pH 6.0; clear smooth lower boundary. (1 to 4 inches thick)

B1--3 to 23 inches; pale brown (10YR 6/3) silt loam, dark grayish brown (10YR 4/2) when moist; weak fine subangular blocky breaking to moderate medium and fine granular structure; very hard when dry, friable when moist; many roots; occasional hard fragments of weathered shale; very strongly acid, pH 4.7; gradual smooth lower boundary. (10 to 26 inches thick)

B2--23 to 28 inches; pale brown (10YR 6/3) light clay loam, dark brown (10YR 4/3) when moist; weak medium subangular blocky breaking to moderate fine and very fine granular structure; very hard when dry, friable when moist; common thin discontinuous clay films; common roots; numerous small hard shale fragments; very strongly acid, pH 4.7; gradual smooth lower boundary. (3 to 8 inches thick)

B3--28 to 36 inches; brown (10YR 5/3) gravelly (cherty) silty clay loam, dark brown (10YR 4/3) when moist with few, distinct, yellowish brown stains on surfaces of chert and shale fragments; massive very hard when dry, firm when moist; common thin discontinuous clay films on surfaces of rock fragments; few large roots; very strongly acid, pH 5.); clear irregular lower boundary. (6 to 12 inches thick)

Dr 36+ inches; light gray (10YR 6/1) fractured, bedded Monterey shale that is slightly weathered in the upper part; less weathered, less fractured and harder below; dark grayish brown (10YR 4/2) when moist; few large tree roots; surfaces of rock along cracks have thin clay films of yellowish brown color.

TYPE LOCATION: About 15 feet north of road at a point 1 1/2 miles east of Cloverdale Road, along China Grade Road, near the center of the southeast quarter of sec. 20, T. 8 S., R. 4 W.

RANGE IN CHARACTERISTICS: The Butano soils occur at elevations usually above 600 feet in a subhumid mesothermal climate having a mean annual rainfall of 30 to 50 inches with warm, dry but somewhat foggy summers and cool, wet winters; an average January temperature of about 50 degrees F; an average July temperature of about 57 degrees F; a and a

Characteristically the Butano soils have thin medium acid, light brownish gray A1 horizons that grade into very strongly acid, brown B2 horizons. The clay content gradually increases to the parent rock which is fractured in the upper portion.

Variations are mainly in depth to bedrock and in color and texture of B2 horizon. On steeper slopes, the B2 may be weak and only slightly more clayey than the A. In slightly concave positions the depth to bedrock is greater than at the type location possibly due to some additions to the surface by colluvial deposition. Also the B2 tends to be of somewhat redder hue and slightly more clayey than on plane or convex slopes. The proportion of shale fragments above the Cr is variable from place to place. Loam and gravelly loam types have been recognized.

COMPETING SERIES: They resemble the Hugo, Lobitos, Melbourne, Mendocino, and Santa Lucia soils. All of these soils except the Santa Lucia developed on less siliceous rocks. The Hugo soils lack textural B horizons and usually are underlain by relatively soft sandstone to considerable depths. The Lobitos soils have thick dark A1 horizons and are slightly acid throughout. The Melbourne soils contain many iron and manganese cemented pellets, have redder B2 horizons (7.5YR hues) and are about moderately fine to fine textured throughout. The Mendocino soils have moderately developed (compact clay loam), reddish yellow B2 horizons overlying deeply weathered, soft sandstone. The Santa Lucia soils are formed on similar rocks to the Butano but have gray A horizons, usually are shaley, and lack textural B horizons.

GEOGRAPHIC SETTING: Sloping to hilly and steep uplands in the Coast Range. Minor bodies are found on sloping ridge crests and alluvial-colluvial fans.frost-free season which probably exceeds 250 days.

GEOGRAPHICALLY ASSOCIATED SOILS: The Butano soils occur in the same general area as the Hugo and Josephine soils.

DRAINAGE AND PERMEABILITY: Well drained; rapid to moderate runoff; moderate permeability.

USE AND VEGETATION: Native cover consists of Douglas fir and redwood forest, with some madrone, oak, ceanothus, poison oak and scattered perennial grasses. Soils are used almost exclusively for forestry, recreation and water supply. A few cutover patches are grazed and a very few are tilled.

DISTRIBUTION AND EXTENT: The soil is extensive in the mountains of southern San Mateo and northern Santa Cruz Counties.The Butano soils occur in the Coast Range Mountains of central eastern California and are used for timber production.


SERIES ESTABLISHED: Soil Survey of San Mateo County, 1959. Source of name, Butano Creek, San Mateo County, California.

REMARKS: This soil is classified as follows: USDA Yearbook: Yellowish brown Lateritic. Revised classification: 8.230, Univ. of Calif. Storie and Weir: Podzolic, Profile Group VIII.

Last revised by the state on 4/60.

National Cooperative Soil Survey