LOCATION ARROWHEAD CAEstablished Series
TAXONOMIC CLASS: Clayey-skeletal, mixed, active, mesic Ultic Haploxeralfs
TYPICAL PEDON: Arrowhead extremely gravelly sandy loam, on a north facing rolling slope of 15 percent under chamise, manzanita, and scrub oak at 2,440 feet elevation. (Colors are for dry soil unless otherwise stated. When described on September 7, 1979, the soil was dry to 34 inches and moist below).
A1--0 to 1 inch; brown (10YR 5/3) extremely gravelly sandy loam, very dark grayish brown (10YR 3/2) moist, moderate fine and medium subangular blocky structure; loose, very friable, nonsticky and nonplastic; many very fine, fine and medium roots; common very fine intersitial and few fine and medium tubular pores; slightly acid (pH 6.5); abrupt wavy boundary. (1 to 2 inches thick)
A2--1 to 4 inches; brown (10YR 5/3) gravelly sandy loam, very dark grayish brown (10YR 3/2) moist; moderate fine and medium subangular blocky structure; loose, very friable, nonsticky and nonplastic; many very fine, fine and few medium roots; common very fine interstitial and few fine and medium tubular pores; 15 percent angular obsidian pebbles 2 to 25 mm in diameter; slightly acid (pH 6.5); abrupt wavy boundary. (2 to 4 inches thick)
BAt--4 to 8 inches; brown (7.5YR 5/3) gravelly sandy loam, dark brown (7.5YR 4/3) moist; weak fine and medium subangular blocky structure; soft, very friable, nonsticky and nonplastic; many very fine and fine, common medium, and few coarse roots; many very fine and fine interstitial and common medium, few coarse tubular pores; 25 percent angular obsidian pebbles 2 to 25 mm in diameter; few thin clay films in pores; slightly acid (pH 6.5); clear irregular boundary. (3 to 6 inches thick)
Bt1--8 to 14 inches; light brown (7.5YR 6/4) gravelly sandy clay loam, yellowish red (5YR 5/6) moist; moderate medium and coarse subangular blocky structure; slightly hard, friable, slightly sticky and nonplastic; many very fine and fine and common medium and coarse roots; many very fine and fine interstitial and common medium, few coarse tubular pores; few thin clay films in pores; 25 percent angular obsidian pebbles 2 to 25 mm in diameter, slightly acid (pH 6.5); gradual wavy boundary. (4 to 10 inches thick).
Bt2--14 to 31 inches; reddish yellow (7.5YR 6/6) very stony clay, strong brown (7.5YR 5/6) moist; weak very fine angular blocky structure; hard, firm, sticky and plastic; few very fine and fine, common medium and few coarse roots; many very fine and common fine interstital and few fine and medium tubular pores; common thin and moderately thick clay films on peds and in pores; 20 percent angular obsidian cobbles 75 to 150 mm in diameter and 35 percent angular obsidian stones; slightly acid (pH 6.5); gradual irregular boundary. (10 to 20 inches thick).
R--31 inches; hard, slightly weathered, fractured obsidian with soil filled fractures 5 to 40 mm wide and 80 to 400 mm apart.
TYPE LOCATION: Lake County, California; 2,800 feet east of Bottlerock Road, approximately 3 miles south of its intersection with Cold Creek Road, 1,240 feet west and 600 feet south of the northeast corner of sec. 7, T. 12 N., R. 8 W; Kelseyville Quadrangle.
RANGE IN CHARACTERISTICS: Depth to a lithic contact with obsidian is 20 to 40 inches. The mean annual soil temperature is 54 to 59 degrees F. The soil between the depth of 8 to 28 inches is dry in all parts from July 1 to October 15 and is moist in all parts from January 1 to April 15. The particle size class ranges from 35 to 45 percent clay. It is neutral or slightly acid throughout. Mineralogy is influenced by amourphous material. Coarse and very coarse sand ranges from 5 to 10 percent throughout. Base saturation is 50 to 75 percent throughout.
The A horizon dry color is 7.5YR 6/3, 7/3; 10YR 5/3, 6/4 or 7/4. Moist color is 7.5YR 5/3, 6/3; 10YR 3/2, 4/2 or 4/3. It is extremely gravelly sandy loam at the surface and gravelly sandy loam in the lower A horizon. Angular obsidian fragments 2 to 25 mm in diameter occur at the surface as a gravel pavement and below that gravel content is 15 to 35 percent.
The Bt horizon dry color is 5YR 6/6, 7/6; 7.5YR 4/6, 6/4, 6/6; 10YR 6/4 or 6/6. Moist color is 5YR 4/6, 5/6, 5/8; 7.5YR 4/3, 4/4, 5/6 or 10YR 6/4. It is gravelly clay loam, gravelly sandy clay loam, cobbly clay loam, very cobbly clay or very stony clay. The weighted average in the upper 20 inches of the argillic is 35 to 45 percent clay and 35 to 60 percent rock fragments. Rock fragments consist of 10 to 45 percent pebbles, 5 to 30 percent cobbles and 0 to 30 percent stones. Some pedons have a B3 horizon.
COMPETING SERIES: This is the Soulajule series in the same family and the Whispering series in another family. Soulajule soils have a paralithic contact at depths of 20 to 40 inches, lack amorphous properties and obsidian. Whispering soils are loamy, skeletal.
GEOGRAPHIC SETTING: The Arrowhead soils occur on volcanic flows. Slopes are 5 to 50 percent. Elevations are 1,500 to 3,000 feet. The soils are formed in material weathered from obsidian. The climate is subhumid mesothermal with hot dry summers and cool moist winters. Mean annual precipitation is 30 to 50 inches. Mean January temperature is 50 degrees F.; mean July temperature is 65 degrees F.; and mean annual temperature is 56 degrees F. The frost free season is 150 to 195 days.
GEOGRAPHICALLY ASSOCIATED SOILS: These are the Bottlerock (T), Glenview (T) and Sodabay (T) soils. Bottlerock, Glenview, and Sodabay soils are all greater than 60 inches to a lithic contact.
DRAINAGE AND PERMEABILITY: Well drained; slow to rapid runoff; moderately slow permeability.
USE AND VEGETATION: Used mainly for watershed and wildlife habitat. Natural vegetation consists of chamise, manzanita, and scrub oak. Chamise appears to be a transitory plant because of a long history of burns.
DISTRIBUTION AND EXTENT: Clear Lake volcanic field, Lake County, California. The series is not extensive.
MLRA SOIL SURVEY REGIONAL OFFICE (MO) RESPONSIBLE: Davis, California
SERIES ESTABLISHED: Lake County, California 1980.
REMARKS: Soils formerly mapped as Hesse Series are now included in the Arrowhead Series.
The activity class was added to the classification in January of 2003. Competing series were not checked at that time. There is no lab data available, this soil possibly has isotic mineralogy - ET