LOCATION LAS POSAS CAEstablished Series
TAXONOMIC CLASS: Fine, smectitic, thermic Typic Rhodoxeralfs
TYPICAL PEDON: Las Posas loam, cultivated. (Colors are for dry soil unless otherwise noted.)
Ap--0 to 7 inches; reddish brown (5YR 4/4) loam, dark reddish brown (5YR 3/4) moist; weak medium granular structure; hard, friable, slightly sticky and slightly plastic; many very fine roots; many very fine interstitial pores; slightly acid (pH 6.2); clear smooth boundary. (2 to 8 inches thick)
A3--7 to 12 inches; reddish brown (5YR 4/4) clay loam, dark reddish brown (5YR 3/4) moist; moderate medium angular blocky structure; hard, firm, sticky and plastic; many very fine roots; common very fine tubular pores; slightly acid (pH 6.2); clear wavy boundary. (4 to 10 inches thick)
B21t--12 to 17 inches; dark red (2.5YR 3/6 dry and moist) clay; strong coarse angular blocky structure; very hard, very firm, very sticky and very plastic; common very fine exped roots; common very fine tubular pores; continuous thick clay films in pores and on faces of peds; neutral (pH 7.0); gradual smooth boundary. (4 to 11 inches thick)
B22t--17 to 27 inches; dark red (2.5YR 3/6 dry and moist) clay; strong medium angular blocky structure; very hard, very firm, very sticky and very plastic; common very fine roots (mostly in cracks along faces of peds); few very fine tubular pores; continuous thick clay films in pores and on faces of peds; neutral (pH 7.3); clear wavy boundary. (4 to 14 inches thick)
B3t--27 to 32 inches; red (2.5YR 4/6) heavy clay loam, dark red (2.5YR 3/6) moist; strong medium angular blocky structure; very hard, firm, sticky and plastic; few very fine roots; few very fine tubular pores; many moderately thick clay films line pores and on faces of peds; neutral (pH 7.3); clear wavy boundary. (3 to 21 inches thick)
C1r--32 to 40 inches; yellowish red (5YR 5/6) weathered fine grained gabbro, yellowish red (5YR 4/6) moist; neutral (pH 7.3); clear smooth boundary. (8 to 16 inches thick)
C2r--40 to 54 inches; pale brown (10YR 6/3) weathered gabbro; neutral (pH 7.0).
TYPE LOCATION: Riverside County, California; about 8 miles northeast of Temecula, California; approximately 500 feet east and 1,000 feet north of the W1/4 corner section 18, T.7S., R.1W.
RANGE IN CHARACTERISTICS: Depth to a paralithic contact is 20 to 40 inches. The mean annual soil temperature is 60 to 65 degrees F. and the soil temperature is never below 47 degrees F. The soils are continuously moist in some part between depths of 4 and 12 inches from about December 1 until late May and are continuously dry the rest of the time. Some pedons have up to 25 percent gravel in some or all horizons but particularly near the surface and near the lithic contact. In addition to gravel, some of these pedons have up to 5 percent cobblestones.
The A horizon is brown to reddish brown (7.5YR 5/2, 5/4, 4/2, 4/4, 3/2; 5YR 5/3, 5/4, 4/3, 4/4). It is fine sandy loam, loam or clay loam and is slightly acid or neutral.
The B2t horizon is reddish brown, dark reddish brown, red or dark red (2.5YR 4/4, 4/3, 4/6, 3/4, 3/6). It is heavy clay loam or clay and averages 35 to 45 percent clay. This horizon is neutral or mildly alkaline.
The C horizon is yellowish red or pale brown.
COMPETING SERIES: These are the Argonaut, Contra Costa, Fancher, Gilroy, Guenoc, Perkins, Sobrante, and Trabuco series in other families. Argonaut, Contra Costa, Fancher, Gilroy, Perkins, Sobrante and Trabuco soils have hue of 5YR or yellower in some part of the argillic horizon. Guenoc soils have kaolinitic clay mineralogy in the argillic horizon.
GEOGRAPHIC SETTING: The La Pasos soils are in uplands at elevations of 200 to 3,000 feet. Slopes are 5 to 50 percent. The soils formed in material weathered from basic igneous rocks. Some areas have up to 10 percent rock outcrop. The climate is dry subhumid mesothermal with warm, dry summers and cool, moist winters. The mean annual precipitation is 12 to 18 inches. The average January temperature is 48 degrees F.; the average July temperature is 72 degrees F; and the mean annual temperature is 62 degrees F. The frost free season is 240 to 320 days.
GEOGRAPHICALLY ASSOCIATED SOILS: These are the competing Fancher soils and the Delpedra, Escondido, Honcut, Toomes and Yokohl soils. Delpedra and Toomes soils have a lithic contact at a depth of less than 20 inches. Escondido soils lack an argillic horizon and have a coarse, loamy control section. Honcut soils lack an argillic horizon and are coarse, loamy. Yokohl soils have a strongly cemented duripan.
DRAINAGE AND PERMEABILITY: Well drained; medium to rapid runoff; slow permeability.
USE AND VEGETATION: Used for growing irrigated citrus fruit, truck crops, and pasture, grain or grain hay. Vegetation in uncultivated areas is mainly annual grasses, forbs, and broadleaf chaparral.
DISTRIBUTION AND EXTENT: Foothills of southern California and the Sierra Nevada. The soils are moderately extensive.
MLRA SOIL SURVEY REGIONAL OFFICE (MO) RESPONSIBLE: Davis, California
SERIES ESTABLISHED: San Diego County (Oceanside Area), California, 1929.