LOCATION ILLER CA

Established Series
Rev. JJN/TDC/ET
12/2022

ILLER SERIES

The Iller series consists of very deep, well drained soils that formed in volcanic ash deposits over colluvium and material weathered from tuff, tuff breccias, or extrusive igneous bedrock. Iller soils are on mountains and have slopes of 9 to 50 percent. The mean annual precipitation is about 40 inches and mean annual temperature is about 42 degrees F.

TAXONOMIC CLASS: Medial over loamy-skeletal, mixed over isotic, frigid Andic Dystroxerepts

TYPICAL PEDON: Iller stony sandy loam - on east facing convex slope of 10 percent under white fir, red fir, ponderosa pine, chinquapin and snowberry at 6,320 feet elevation. (Colors are for dry soil unless otherwise noted. When described (6/6/74) the soil was moist throughout.)

01 and 02--1 inch to 0; new and partially decomposed needles, bark, twigs, leaves and other organic debris; abrupt smooth boundary. (0 to 4 inches thick)

A11--0 to 2 inches; brown (7.5YR 4/4) stony sandy loam, dark reddish brown (5YR 3/2) moist; weak fine granular structure; soft, very friable, slightly sticky and nonplastic; few very fine and fine roots; few fine tubular and many very fine interstitial pores; 7 percent pebbles, 2 percent cobbles and 7 percent stones; weakly smeary; strongly acid (pH 5.5); abrupt smooth boundary. (2 to 4 inches thick)

A12--2 to 13 inches; brown (7.5YR 5/4) stony sandy loam, dark brown (7.5YR 3/2) moist; weak medium subangular blocky structure; slightly hard, very friable, slightly sticky and nonplastic; common very fine and fine roots; few fine tubular and many very fine interstitial pores; 15 percent pebbles, cobbles and stones; weakly smeary; strongly acid (pH 5.5); clear smooth boundary. (8 to 13 inches thick)

B1--13 to 21 inches; brown (7.5YR 5/4) sandy loam, dark reddish brown (5YR 3/3) moist; weak medium subangular blocky structure; slightly hard, very friable, slightly sticky and nonplastic; few very fine and fine and many medium roots; few fine tubular and many very fine interstitial pores; 7 percent pebbles, 2 percent cobbles, and 1 percent stones; weakly smeary; strongly acid (pH 5.5); gradual wavy boundary. (0 to 9 inches thick)

B2t--21 to 28 inches; brown (7.5YR 5/4) sandy loam, dark reddish brown (5YR 3/3) moist; moderate medium subangular blocky structure; slightly hard, very friable, slightly sticky and nonplastic; few very fine, fine and many medium and coarse roots; common very fine and fine vesicular and few very fine tubular pores; few thin clay films on peds and in pores and many thin clay films as bridges between sand grains; 7 percent pebbles, 2 percent cobbles, 1 percent stones; moderately smeary; strongly acid (pH 5.5); abrupt wavy boundary. (10 to 14 inches thick)

IIB1tb--28 to 37 inches; yellowish brown (10YR 5/4) very stony sandy loam, dark reddish brown (5YR 3/4) moist; strong medium subangular blocky structure parting to strong fine subangular blocky; slightly hard, friable, sticky and slightly plastic; few very fine, and many medium and coarse roots; common very fine vesicular and few very fine tubular pores; common thin clay films on peds and in pores; slightly brittle; 15 percent pebbles, 5 percent cobbles and 30 percent stones; strongly acid (pH 5.5); abrupt wavy boundary. (4 to 11 inches thick)

IIB21tb--37 to 42 inches; brown (7.5YR 5/4) extremely stony loam, dark reddish brown (5YR 3/4) moist; strong medium subangular blocky structure; hard, friable, sticky and plastic, few very fine and fine, and many medium roots; common very fine vesicular and few very fine tubular pores; common thin clay films on peds and in pores; slightly brittle; 10 percent pebbles, 10 percent cobbles and 50 percent stones; strongly acid (pH 5.5); clear wavy boundary. (2 to 7 inches thick)

IIB22tb--42 to 54 inches; brown (7.5YR 5/4) extremely stony loam, brown (7.5YR 5/4) extremely stony loam, dark brown (7.5YR 3/4) moist; massive; hard, friable, sticky and plastic; few very fine and fine, and many medium roots; common very fine vesicular and few very fine tubular pores; common thin and few moderately thick clay films on faces of rock fragments; 10 percent pebbles, 10 percent cobbles and 50 percent stones; slightly brittle; strongly acid (pH 5.5); clear wavy boundary. (4 to 14 inches thick)

IIB23tb--54 to 65 inches; brown (7.5YR 5/4) extremely stony loam, brown (7.5YR 5/4) extremely stony loam, dark brown (7.5YR 3/4) moist; massive; hard, friable, sticky and plastic; few very fine, fine and many medium roots; common very fine vesicular and few very fine tubular pores, common thin and few moderately thick clay films on faces of rock fragments; slightly brittle; 10 percent gravel, 10 percent cobbles and 50 percent stones; strongly acid (pH 5.5).

TYPE LOCATION: Siskiyou County California; about 20 miles NE of Weed on Hwy. 97 on the eastern slopes of Miller Mountain or about 1 3/4 miles N of Herd Peak Lookout; about 1,525 feet west and 100 feet south of the northeast corner sec. 19, T. 44 N., R. 3 W.

RANGE IN CHARACTERISTICS: The volcanic ash mantle is 20 to 30 inches thick. Depth to a paralithic contact of weathered basalt is greater than 60 inches. The mean annual soil temperature is 42 to 47 degrees F. The soil temperature exceeds 41 degrees F. from May 1 to November 10 and exceeds 47 degrees F. from June 1 to October 20. The soil is dry in the 8 to 24 inch moisture control section from mid-July to mid-October and is moist in some or all parts the rest of the year. The bulk density ranges from 0.6 to 1 g/cc to a depth of 10 to 20 inches but is 0.85 g/cc at a depth of 10 to 14 inches. There are 5 to 35 percent angular or subangular rock fragments of andesite or basalt in the ash deposits to depths of 20 to 30 inches. The fragments commonly are cobbles and stones but range from fine gravel to a few large boulders. The buried soil material has 35 to 80 percent rock fragments that are similar to the overlying ash deposits. In addition there is saprolitic gravel and cobbles that make up 5 to 15 percent in the buried horizons. The soil is slightly acid to strongly acid.

The A horizon is dark grayish brown, grayish brown, brown, dark reddish gray, reddish gray, or reddish brown (10YR 4/2, 4/3, 5/2, 5/3; 7.5YR 4/2, 4/4, 5/2, 5/4; 5YR 4/2, 4/3, 5/2, 5/3). Moist colors are very dark gray, dark brown, or dark reddish brown (10YR 3/2, 3/3; 7.5YR 3/2; 5YR 3/2, 3/3). The base saturation ranges from 40 to 60 percent but is less than 50 percent in at least part of the upper 10 inches. The NaF pH ranges from 9.6 to 10.7. Clay content ranges from 3 to 10 percent.

The B2t horizon is brown, yellowish brown, pale brown, light yellowish brown, reddish brown, or light reddish brown (10YR 5/3, 5/4, 6/3, 6/4; 7.5YR 5/4, 6/4; 5YR 5/3, 5/4, 6/3, 6/4). Moist colors range from dark brown to reddish brown or dark yellowish brown (10YR 3/3, 3/4, 4/3, 4/4; 7.5YR 4/4; 5YR 3/3, 3/4, 4/3, 4/4). Clay content is about 5 to 12 percent and has only 1 to 2 percent increase in clay over the A horizon. Commonly there are a few thin clay films in the lower part of the B1 or B2t horizons. The base saturation ranges from 30 to 60 percent. The NaF pH 1s 9.0 to 10.0.

The IIBtb horizon colors are similar to the B2t horizon. It is very stony sandy loam, extremely stony loam, or extremely stony sandy clay loam and has 5 to 12 percent clay in the lower part. The base saturation is 50 to 60 percent and commonly increases slightly with depth. The NaF pH ranges from 8.5 to 9.0. This horizon has slightly less influence from amorphous materials.

COMPETING SERIES: This is the Sheld series in another family. Sheld soils have greater than 35 percent rock fragments throughout the soil.

GEOGRAPHIC SETTING: Iller soils are on older surfaces of volcanic uplands where more recent volcanic ash has been deposited over materials weathered from tuff, tuff breccias, or hard andesite or basaltic bedrock. Slopes are 9 to 50 percent. Elevations are 5,000 to 7,500 feet. The climate is continental and subhumid with warm nearly dry summers and cold moist winters. Mean annual precipitation is 20 to 45 inches. Snowfall is 24 to 48 inches, and covers the higher elevations from late November to early April in most years. Mean January temperature is 22 to 28 degrees F.; mean July temperature is 59 to 64 degrees F.; mean annual temperature is 37 to 45 degrees F. Frost-free season is 35 to 60 days.

GEOGRAPHICALLY ASSOCIATED SOILS: These are the Avis, Bogus, Esro, Oosen, Orset, Pinehurst and the competing Sheld soils. Avis and Oosen soils have an ochric epipedon and an ashy or ashy skeletal control section. Bogus soils have a thick mollic epipedon and a fine textured argillic horizon. Esro soils have an aquic moisture regime and a fine-silty control section. Orset soils have an ochric epipedon and a coarse-loamy control section. Pinehurst soils have a thick mollic epipedon and a fine-loamy argillic horizon.

DRAINAGE AND PERMEABILITY: Well drained, slow to rapid runoff, moderate permeability.

USE AND VEGETATION: Used mainly for timber. Native vegetation is white fir, red fir, ponderosa pine, incense cedar and some Douglas-fir at lower elevations. Shrubs are wild currant, greenleaf manzanita, prostrate ceanothus, snowbrush and chinquapin.

DISTRIBUTION AND EXTENT: Cascade Range of northern California. Moderately extensive and may occur in southern Oregon.

MLRA SOIL SURVEY REGIONAL OFFICE (MO) RESPONSIBLE: Davis, California

SERIES ESTABLISHED: Siskiyou County, California, 1978.

REMARKS: This soil has an umbric epipedon and a cambic horizon above the buried IIBtb horizon. The soil in the upper 20 to 30 inches or above the IIBtb horizon is the basis for classification.

The classification was updated in February 2001 using the Eighth Edition to Soil Taxonomy. This series was formerly classified as Medial over loamy-skeletal, mixed, frigid Andic Xerumbrepts. Competing series were not checked at that time.

ADDITIONAL DATA: Sampled for characterization 6/74 by the Riverside Laboratory, pedon No. S74-CA-093-6.

OSED scanned by SSQA. Last revised by state on 10/78.

National Cooperative Soil Survey
U.S.A.