LOCATION CRONKHITE CAEstablished Series
TAXONOMIC CLASS: Fine, smectitic, isomesic Pachic Argiustolls
TYPICAL PEDON: Cronkhite heavy loam, on a west facing convex slope of 45 percent under coyotebrush, sage, lupine, brackenfern, poison-oak, blackberry, ryegrass, and toyon at 200 feet elevation. (Colors are for dry soil unless otherwise stated. When described (9/21/76) the soil was moist below 26 inches.)
A11--0 to 9 inches; brown (10YR 5/3) loam, very dark gray (10YR 3/1) moist; strong very fine, fine, and medium subangular blocky structure; extremely hard, friable, slightly sticky and slightly plastic; common very fine and few medium roots; common very fine tubular and interstitial, common fine tubular and vesicular pores; cracks 5mm wide, 6 to 12 inches apart; slightly acid (pH 6.3); clear smooth boundary. (8 to 11 inches thick)
A12--9 to 15 inches; dark grayish brown (10YR 4/2) loam, very dark grayish brown (10YR 3/2) moist; moderate very fine, fine, and medium subangular blocky structure; very hard, friable, slightly sticky and slightly plastic; common very fine roots; common very fine tubular and vesicular pores; cracks 5mm wide, 6 to 12 inches apart; slightly acid (pH 6.3); gradual smooth boundary. (5 to 8 inches thick)
A3--15 to 26 inches; dark grayish brown (10YR 4/2) clay loam, very dark grayish brown (10YR 3/2) moist; moderate very fine and fine subangular blocky structure; extremely hard, friable, sticky and plastic; common very fine roots; common very fine interstitial and tubular, common fine and medium tubular and vesicular pores; common moderately thick clay films in pores; many pressure faces; cracks 0.5cm wide, about 6 to 12 inches apart; slightly acid (pH 6.3); abrupt smooth boundary. (10 to 13 inches thick)
B2t--26 to 37 inches; mixed colors of yellowish brown and strong brown (10YR 5/8 and 7.5YR 5/8) clay, dark grayish brown and very dark grayish brown (10YR 4/2, 3/2) moist; moderate coarse and very coarse angular blocky structure; extremely hard, firm, sticky and plastic; common very fine and few fine roots; common very fine tubular, vesicular, and interstitial pores; many moderately thick clay films in pores; many pressure faces; cracks 5mm wide and about 4 to 8 inches apart; slightly acid (pH 6.3); gradual wavy boundary. (10 to 16 inches thick)
B3t--37 to 45 inches; yellowish brown (10YR 5/8) clay loam, dark yellowish brown (10YR 4/4) moist; strong medium and coarse angular blocky structure; very hard, friable, sticky and plastic; common very fine and few fine roots; common very fine tubular, vesicular, and interstitial pores; many moderately thick clay films in pores; many pressure faces; cracks 10mm apart, about 4 to 8 inches apart; neutral (pH 6.8); gradual irregular boundary. (7 to 12 inches thick)
Cr--45 to 55 inches; highly shattered weathered sandstone with prominent dark stains. Fragments slake in water.
TYPE LOCATION: Marin County, California; in the Golden Gate National Recreation Area, 400 feet up hill east of Muir Woods Road, 1/2 mile NW of the intersection of Shoreline Hwy and Muir Woods Road.
RANGE IN CHARACTERISTICS: Depth to the paralithic contact is 40 to 60 inches. The mean annual soil temperature is about 53 degrees to 58 degrees F. The difference between mean summer and mean winter temperatures is less than 9 F. The soil moisture control section is usually moist in all parts from mid-November to June. It is dry in some or all parts the rest of the time but is not dry in all parts for 45 consecutive days. The soil is slightly acid or neutral and commonly becomes less acid with increasing depth. Organic matter is more than 1 percent to a depth of 20 inches or more. Base saturation is more than 50 percent throughout the profile and increases with increasing depth.
The A horizon has dry color of 10YR 4/2, 5/2 or 5/3, and moist color of 10YR 2/1, 3/2 or 3/3.
The Bt horizon has variegated dry color of 10YR 5/6, 5/8, 6/6; 7.5YR 4/2, 5/2 or 5/8 and moist color of 10YR 3/2, 4/2, 4/3 or 4/4. It is clay or clay loam and has 35 to 50 percent clay. The upper boundary of the Bt horizon is abrupt with less than 15 percent absolute clay increase from the A horizon.
COMPETING SERIES: These are the Olompali and Tomales series in other families. Olompali and Tomales soils have a mesic soil temperature and an umbric epipedon.
GEOGRAPHIC SETTING: Cronkhite soils are on hills. Slopes are 9 to 75 percent. The soils formed in material weathered from sandstone and shale. Elevations are 50 to 800 feet. The climate is subhumid mesothermal with cool foggy summers and cool moist winters. Mean annual precipitation is 24 to 35 inches. Mean January temperature is about 52 degrees F.; mean July temperature is about 55 degrees F.; mean annual temperature is about 52 degrees to 57 degrees F. Frost-free season is 275 to 300 days.
GEOGRAPHICALLY ASSOCIATED SOILS: These are the Barnabe, Centissima, Dipsea and Tocaloma soils and the competing Olompali soils. Barnabe soils are less than 20 inches deep to a lithic contact. Centissima soils are 20 to 40 inches deep to a paralithic contact and have a fine-loamy particle-size control section. Dipsea soils lack a mollic epipedon and have a loamy-skeletal particle-size control section. Tocaloma soils are 20 to 40 inches deep to a paralithic contact and lack an argillic horizon.
DRAINAGE AND PERMEABILITY: Moderately well drained; medium to very rapid runoff; slow permeability.
USE AND VEGETATION: Used for range, wildlife habitat and recreation. Native vegetation is annual grasses and shrubs.
DISTRIBUTION AND EXTENT: Small extent along central and northern California coast.
MLRA SOIL SURVEY REGIONAL OFFICE (MO) RESPONSIBLE: Davis, California
SERIES ESTABLISHED: Marin County, California, 1979.