Established Series


The San Miguel soils have light yellowish brown, medium acid, silt loam A1 horizons, very pale brown, strongly acid, silt loam A2 horizons, strong brown and yellowish brown, strongly and very strongly acid, clay and gravelly clay B2t horizons over hard metavolcanic bedrock at a depth of 23 inches.

TAXONOMIC CLASS: Fine, smectitic, thermic Typic Natrixeralfs

TYPICAL PEDON: San Miguel silt loam - native shrubs. (Colors are for dry soil unless otherwise noted.)

A1--0 to 4 inches; light yellowish brown (10YR 6/4) silt loam, brown (7.5YR 4/4) moist; massive; slightly hard, friable, nonsticky, nonplastic; common very fine roots; common fine pores; moderately acid (pH 6.0); abrupt wavy boundary. (3 to 8 inches thick)

A2--4 to 8 inches; very pale brown (10YR 7/3) silt loam, yellowish brown (10YR 5/6) moist; massive; hard, friable, nonsticky, slightly plastic; common fine and medium roots; many fine and very fine pores; few continuous clay films lining pores; strongly acid (pH 5.2); abrupt wavy boundary. (0 to 8 inches thick)

Btss1--8 to 18 inches; strong brown (7.5YR 5/6) clay, yellowish red (5YR 4/6) moist; strong coarse prismatic structure; extremely hard, firm, very sticky, very plastic; common fine and medium roots; few fine and medium pores; many moderately thick clay films on faces of peds; few slickensides; strongly acid (pH 5.1); clear wavy boundary. (8 to 16 inches thick)

Btss2--18 to 23 inches; yellowish brown (10YR 5/4) gravelly clay, brown (7.5YR 4/4) moist; moderate medium subangular blocky structure; very hard, friable, very sticky, plastic; common fine and very fine roots; few fine pores; common moderately thick clay films on rock fragments; very strongly acid (pH 5.0); abrupt irregular boundary. (4 to 8 inches thick)

R--23 to 31 inches; gray and dark gray, hard metavolcanic rock with cleavage planes that intersect near right angles, upper 2 or 4 inches of which are weathered to light yellowish brown (2.5Y 6/4) with small amount of yellowish brown soil in cracks.

TYPE LOCATION: San Diego County, California; about 2.5 miles east-southeast of Kuebler Ranch headquarters on Otay Mountain Truck Trail, SW1/4SW1/4 sec. 27, T.19S., R.1E. 32 degrees North latitude, 34 minutes, 09 seconds; 116 degrees West longitude, 52 minutes, 26 seconds; UTM zone 11 3603530n, 51836e NAD 83.

RANGE IN CHARACTERISTICS: Depth to hard rock ranges from 20 to 34 inches. The mean annual soil temperature at a depth of 20 inches is 61 degrees to 64 degrees F. and the soil temperature usually is not below 47 degrees F. at any time. The soil between depths of 4 and 12 inches is usually moist in some or all parts from about December 1 until late May and is continuously dry the rest of the time. The A1 horizon is pale brown, light yellowish brown or very pale brown (10YR 6/3, 6/4, 7/4) silt loam or loam and is slightly or medium acid. In some pedons the A2 horizon is discontinuous. The B2t horizon is yellowish brown, strong brown, reddish brown or yellowish red (10YR 5/4); 7.5YR 5/6; 5YR 5/3, 5/4, 4/4, 4/6, 5/6) clay loam, silty clay loam or clay and has 35 to 45 percent clay. It is slightly acid to very strongly acid. The A-B2t horizon boundary is abrupt and the absolute clay increase is greater than 15 percent. Exchangeable sodium percentage in all parts of the B2t horizon is 15 to 25.

COMPETING SERIES: These are the Antioch, Bonsall, Las Flores, Lethent, Milpitas, Placentia, Riz, Solano, San Ysidro, Stockpen, Tierra, and Waukena series. These series lack a lithic or paralithic contact above a depth of 40 inches.

GEOGRAPHIC SETTING: The San Miguel soils are strongly sloping to very steep and are in mountainous areas at elevations of 700 to 3,300 feet. The soils formed in residuum weathered from metavolcanic rocks. The climate is subhumid mesothermal with warm dry summers and cool moist winters. The mean annual precipitation is 13 to 18 inches. The average January temperature is about 48 degrees F., average July temperature is about 75 degrees F., and mean annual temperature is 59 to 62 degrees F. The frost-free season is 240 to 280 days.

GEOGRAPHICALLY ASSOCIATED SOILS: These are the Auld, Escondido, Exchequer, and Friant soils. Each of the associated soils lack natric horizons. Auld soils are fine textured throughout and have intersecting slickensides. Escondido soils lack argillic horizons. Exchequer soils have lithic contacts at depths of less than 20 inches. Friant soils have mollic epipedons and have lithic contacts at depths of less than 20 inches.

DRAINAGE AND PERMEABILITY: Well-drained; medium to very rapid runoff; very slow permeability.

USE AND VEGETATION: Used for limited grazing, watershed, and recreation. Native vegetation is chaparral, chamise, ceanothus, sumac, yerba santa, and bear clover.

DISTRIBUTION AND EXTENT: Southern California mountains. The soils are moderately extensive.


SERIES ESTABLISHED: San Diego County, California, 1973.

REMARKS: The San Miguel soils were formerly classified as (maximal) Noncalcic Brown soils.

ADDITIONAL DATA: NSSL pedons S64CA-073-018 (type location) and S66CA-073-005 (taxadjunct).

OSED scanned by SSQA. Last revised by state on 10/73.
UTM and Latitude and Longitude added 2/2009 ET

National Cooperative Soil Survey