LOCATION SIRDRAK CAEstablished Series
TAXONOMIC CLASS: Sandy, mixed, isomesic Humic Dystrustepts
TYPICAL PEDON: Sirdrak sand - on a northwest facing hummocky slope of 1 percent under lupine, ripgut brome, fiddleneck, filaree, wild oat, and soft chess at 90 feet elevation. (Colors are for dry soil unless otherwise stated. When described April 24, 1974, the soil was moist throughout).
A1--0 to 16 inches: very dark grayish brown (10YR 3/2) sand, very dark brown (10YR 2/2) moist; single grained; loose, very friable; many very fine, fine and few coarse roots; many very fine interstitial pores; moderately acid (pH 6.0); clear smooth boundary. (2 to 20 inches thick)
A2--16 to 36 inches; very dark grayish brown (10YR 3/2) sand, very dark brown (10YR 2/2) moist; massive; soft, very friable; few fine and common medium roots; many very fine interstitial pores; slightly acid (pH 6.3); clear smooth boundary. (10 to 30 inches thick)
AC--36 to 48 inches; dark yellowish brown (10YR 4/4) sand, very dark grayish brown (10YR 3/2) moist; massive; slightly hard, very friable; few fine and common medium roots; many very fine interstitial pores; slightly acid (pH 6.3); clear wavy boundary. (6 to 15 inches thick)
C--48 to 62 inches; yellowish brown (10YR 5/4) sand, dark yellowish brown (10YR 4/4) moist; massive; slightly hard, very friable; few fine and medium roots; many very fine interstitial pores; slightly acid (pH 6.5).
TYPE LOCATION: Marin County, California; Point Reyes National Seashore; about 400 feet NE of intersection of Pierce Point Road and north entrance to McClure Ranch on access road and about 100 feet south in field.
RANGE IN CHARACTERISTICS: The mean annual soil temperature is 50 to 56 degrees F and the soil temperature usually is not below 47 degrees F at any time. The difference between mean winter and mean summer temperature is less than 9 degrees F. Soil between the depths of 12 and 36 inches is usually moist from mid-November to mid-June. It is dry in some part the rest of the time. Organic matter ranges from 1 to 5 percent to depths of more than 20 inches and decreases regularly with increasing depth. Reaction is strongly acid to slightly acid. The soil is sand or loamy sand throughout and has 80 to 95 percent sand. Base saturation ranges from 50 to 85 percent in the upper 20 to 24 inches and from 35 to 50 percent at depths of 45 to 60 inches.
The A horizon has dry color of 10YR 4/1, 4/2, 4/3, 3/2 or 3/3 and moist color of 10YR 2/2, 3/2, 3/3, 3/1 or 2/1. It has weak granular structure or is single grained or massive.
The C horizon has dry color of 10YR 6/3, 6/4, 6/6, 5/4, 5/6, 4/3, 4/4; 5Y 7/2, 7/3; or 2.5Y 4/2 7/2, 7/4; ad moist color of 10YR 5/3, 5/4, 4/4, 4/6, 3/2, 3/4; 2.5Y 4/2, 5/4; 5Y 5/3, 6/3.
COMPETING SERIES: There are no competing series.
GEOGRAPHIC SETTING: The Sirdrak soils are on dunes. Slopes are 0 to 50 percent. The soils formed in sandy eolian deposits near the Pacific Ocean at elevations of 20 to 800 feet. The climate is subhumid mesothermal with cool foggy summers and cool moist winters. Mean annual precipitation is 20 to 45 inches. Mean January temperature is 48 to 52 degrees F; mean July temperature is 52 to 56 degrees F; mean annual temperature is about 53 to 57 degrees F. Frost-free period is 250 to 365 days.
GEOGRAPHICALLY ASSOCIATED SOILS: These are the Kehoe, Inverness and Tomales soils. Kehoe and Inverness soils have a fine-loamy particle-size control section and Tomales soils have a fine particle-size control section.
DRAINAGE AND PERMEABILITY: Somewhat excessively drained; very slow to rapid runoff; rapid permeability.
USE AND VEGETATION: Present use is livestock grazing and some hay production. Once the area is completely taken over by the National Park Service, the primary use will be recreation and wildlife habitat. Vegetation is shrub, annual grasses, and forbs.
DISTRIBUTION AND EXTENT: Central and northern coastal California. The series is of small extent. MLRA 4, 14.
MLRA SOIL SURVEY REGIONAL OFFICE (MO) RESPONSIBLE: Davis, California
SERIES ESTABLISHED: Marin County, California, 1979.
REMARKS: Diagnostic horizons and features recognized in this pedon are:
Mollic epipedon - the zone from 0 to 36 inches (A1, A2 horizons)
ADDITIONAL DATA: Riverside Laboratory, Pedon No. S74-CA. 41-5.