LOCATION SISKIYOU           OR+CA
Established Series
Rev. DKS/AON/TDT
01/2000

SISKIYOU SERIES


The Siskiyou series consists of moderately deep, somewhat excessively drained soils that formed in residuum and colluvium weathered from granitic bedrock. Siskiyou soils are on uplands and have slopes of 20 to 90 percent. The mean annual precipitation is about 45 inches and the mean annual temperature is about 49 degrees F.

TAXONOMIC CLASS: Coarse-loamy, mixed, superactive, mesic Typic Dystroxerepts

TYPICAL PEDON: Siskiyou gravelly sandy loam, forested. (Colors are for moist soil unless otherwise noted.)

A--0 to 4 inches; very dark grayish brown (10YR 3/2) gravelly sandy loam, grayish brown (10YR 5/2) dry; weak very fine granular structure; slightly hard, very friable, nonsticky and nonplastic; many very fine roots; many irregular pores; 20 percent gravel; moderately acid (pH 6.0); clear wavy boundary. (2 to 9 inches thick)

Bw1--4 to 11 inches; dark brown (10YR 4/3) sandy loam, very pale brown (10YR 7/3) dry; weak fine and medium subangular blocky structure; slightly hard, very friable, nonsticky and nonplastic; common irregular pores; common very fine and fine roots; 15 percent gravel; moderately acid (pH 5.6); clear wavy boundary. (3 to 9 inches thick)

Bw2--11 to 19 inches; dark yellowish brown (10YR 4/4) sandy loam, very pale brown (10YR 7/3) dry; weak medium subangular blocky structure; hard, friable, nonsticky and nonplastic; few very fine and fine roots; common irregular pores; 15 percent gravel; moderately acid (pH 5.6); clear wavy boundary. (4 to 9 inches thick)

C1--19 to 31 inches; yellowish brown (10YR 5/4) sandy loam, light gray (10YR 7/2) dry; massive; hard, friable, nonsticky and nonplastic; few roots; common irregular pores; 15 percent gravel; moderately acid (pH 5.6); clear wavy boundary. (5 to 15 inches thick)

C2--31 to 36 inches; yellowish brown (10YR 5/4) sandy loam, light gray and white (10YR 7/2, 8/2) dry; massive; slightly hard, friable, nonsticky and nonplastic; few roots; common irregular pores; strongly acid (pH 5.2); gradual wavy boundary. (4 to 10 inches thick)

Cr--36 inches; weathered granodiorite; dark brown (7.5YR 4/4) stains in fractures.

TYPE LOCATION: Josephine County, Oregon; about 2 miles northwest of Grants Pass and 500 feet northeast of the overpass where Frontage Road crosses Interstate 5; about 750 feet north and 1,060 feet west of the southwest corner of sec. 36, T. 35 S., R. 6 W.; W.M.

RANGE IN CHARACTERISTICS: The soils are usually moist but are dry throughout the moisture control section for 60 to 90 days during the summer. The mean annual soil temperature is 47 to 56 degrees F. Depth to a paralithic contact is 20 to 40 inches and the solum ranges from 12 to 20 inches thick. The particle-size control section is coarse sandy loam or sandy loam with 8 to 12 percent clay and has 15 to 50 percent coarse and very coarse sand. Reaction ranges from slightly acid to strongly acid. The base saturation by ammonium acetate between 10 and 30 inches is 50 to 60 percent.

The A horizon has value of 3 or 4 moist, 4 through 6 dry, and chroma of 2 or 3 moist and dry. It is coarse sandy loam or sandy loam. Gravel content is 10 to 25 percent.

The Bw horizon has hue of 10YR, 7.5YR, or 2.5Y, value of 4 or 5 moist, 5 through 7 dry, and chroma of 2 through 4 moist and dry. It is coarse sandy loam or sandy loam. Gravel content is 10 to 25 percent.

The C horizon has hue of 10YR or 2.5Y, value of 4 or 6 moist, 7 or 8 dry, and chroma of 2 through 4 moist and dry. It is sandy loam or coarse sandy loam. Some pedons have loamy coarse sand in the lower part. Rock fragments are 10 to 25 percent gravel and 0 to 10 percent cobbles; not exceeding a total of 35 percent in the B and C horizons.

COMPETING SERIES: These are the Chaix, Dome, Elwha, Gilligan, Loper, Steinmetz, Tethrick, Ulricher and Vader series. Chaix soils have a mean annual soil temperature of 54 to 59 degrees F. Dome, Gilligan, Steinmetz, Tethrick, Ulricher and Vader soils are over 40 inches deep. Elwha soils are moderately well drained and have dense glacial till (Cr) at 20 to 40 inches. Loper soils have more than 15 percent clay in the particle-size control section.

GEOGRAPHIC SETTING: The Siskiyou soils are on hillslopes and mountain slopes at elevations of 700 to 4,000 feet. Slope gradients range from 20 to 90 percent. The soils formed in colluvium or residuum weathered from granodiorite, quartz diorite or granite. The summers are warm and dry, and winters are cool and moist with an annual precipitation of 35 to 60 inches. The mean annual temperature is 45 to 54 degrees F. The frost-free period is 100 to 200 days.

GEOGRAPHICALLY ASSOCIATED SOILS: These are the competing Tethrick and Hugo and Lettia soils. Lettia soils have a fine-loamy argillic horizon and are deeper than 40 inches to bedrock. Hugo soils are fine-loamy and over 40 inches to bedrock.

DRAINAGE AND PERMEABILITY: Somewhat excessively drained; moderately rapid permeability.

USE AND VEGETATION: Timber production, water supply, wildlife habitat and grazing. Native vegetation is ponderosa pine, sugar pine, Douglas fir, Pacific madrone, common snowberry, and western fescue.

DISTRIBUTION AND EXTENT: Southwestern Oregon and Northern California. The series is of moderate extent.

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

SERIES ESTABLISHED: Medford Area, Oregon, 1911.

REMARKS: Formerly classified as coarse-loamy, mixed, mesic Dystric Xerochrepts, competing series not updated at the time of reclassification.

ADDITIONAL DATA: Characterization data on one profile (S71-Oreg. 17-1) is reported in mimeographed copy from Oregon State University. Engineering test data for the same sample is from the Engineering and Watershed Planning Unit in Portland. The base saturation was sum of cations for this profile; when converted to ammonium acetate, the results verify Dystric placement.


National Cooperative Soil Survey
U.S.A.