LOCATION IRMA                    OR

Established Series
Rev. MHF/CDJ/RWL
06/2011

IRMA SERIES

The Irma series consists of very deep, well drained soils formed in colluvium and residuum from schist or phyllite rock types. Irma soils are on broad ridgetops of mountains. Slopes are 0 to 30 percent. The mean annual precipitation is about 110 inches and mean annual temperature is about 49 degrees F.

TAXONOMIC CLASS: Fine-loamy, mixed, active, mesic Humic Dystrudepts

TYPICAL PEDON: Irma very channery loam - woodland, on a 10 percent east-facing slope at an elevation of 2,260 feet. (When described on July 30, 1990 the soil profile was dry to a depth 14 inches and moist below this depth. (Colors are for moist soil unless otherwise noted.)

Oi--0 to 1 inch; slightly decomposed needles, leaves, twigs and woody materials.

A--1 to 7 inches; dark brown (10YR 3/3) very channery loam, brown (10YR 5/3) dry; weak very fine subangular blocky structure; slightly hard, very friable, slightly sticky and slightly plastic; common very fine and fine, and few medium and coarse roots; common fine and very fine tubular pores; 40 percent channers; very strongly acid (pH 5.0); clear smooth boundary. (6 to 9 inches thick)

BA--7 to 15 inches; brown (10YR 4/3) channery loam, pale brown (10YR 6/3) dry; moderate very fine and fine subangular blocky structure; slightly hard, very friable, slightly sticky and slightly plastic; many fine and medium, and common very fine and coarse roots; many fine and very fine tubular pores; 30 percent channers; strongly acid (pH 5.2); clear smooth boundary. (0 to 11 inches thick)

Bw1--15 to 29 inches; dark yellowish brown (10YR 4/4) channery clay loam, light yellowish brown (10YR 6/4) dry; moderate fine and medium subangular blocky structure; slightly hard, friable, slightly sticky and slightly plastic; common fine and medium, and few very fine and coarse roots; common fine tubular pores; 25 percent channers; strongly acid (pH 5.4); clear smooth boundary.

Bw2--29 to 43 inches; dark yellowish brown (10YR 4/4) channery clay loam, light yellowish brown (10YR 6/4) dry; moderate fine and medium subangular blocky structure; slightly hard, friable, slightly sticky and slightly plastic; few medium roots; few fine tubular pores; 25 percent channers; strongly acid (pH 5.4); clear smooth boundary.

Bw3--43 to 56 inches; yellowish brown (10YR 5/4) channery clay loam, very pale brown (10YR 7/4) dry; moderate medium and coarse subangular blocky structure; slightly hard, friable, slightly sticky and slightly plastic; few medium roots; few fine tubular pores; 25 percent channers; strongly acid (pH 5.2); clear smooth boundary. (Combined thickness of the Bw horizon is 34 to 50 inches)

C--56 to 73 inches; light yellowish brown (10YR 6/4) very channery clay loam, pale yellow (2.5Y 7/4) dry; massive; slightly hard, friable, slightly sticky and moderately plastic; few fine tubular pores; 40 percent channers; strongly acid (pH 5.2).

TYPE LOCATION: Curry County, Oregon; located about 950 feet north and 650 feet west of the southeast corner of section 7, T. 35 S., R. 12 W. (Latitude 42 degrees, 33 minutes, 27 seconds N.; Longitude 124 degrees, 10 minutes, 05 seconds W.)

RANGE IN CHARACTERISTICS: The mean annual soil temperature is 47 to 54 degrees F. The soils are usually moist but are dry for less than 45 consecutive days in all parts between 4 and 12 inches in the four months following the summer solstice. The particle-size control section averages 20 to 30 percent clay and 15 to 30 percent total rock fragments. Depth to bedrock is greater than 60 inches. The solum is 40 to 60 inches thick. Soil reaction is very strongly acid or strongly acid throughout. Hue is 10YR or 7.5YR in the solum.

The A horizon has value of 2 or 3 moist, 4 or 5 dry and chroma of 2 or 3 moist and dry. It is very channery loam with l0 to 25 percent clay. It has 35 to 45 percent channers and 0 to 5 percent flagstones.

The BA horizon has value of 4 or 5 moist, 5 or 6 dry and chroma of 3 or 4 moist and dry. It is channery loam with 20 to 25 percent clay. It has 20 to 30 percent channers and 0 to 3 percent flagstones.

The Bw horizon has value of 4 or 5 moist, 5 through 7 dry and chroma of 4 through 6 moist and dry. It is channery loam or channery clay loam with 20 to 30 percent clay. It has 15 to 30 percent channers and 0 to 3 percent flagstones.

The C horizon has hue of 10YR or 2.5Y, value of 5 or 6 moist, 6 or 7 dry and chroma of 4 through 6 moist and dry. It is channery loam, channery clay loam, or very channery clay loam averaging 15 to 30 percent clay. It has 25 to 50 percent channers and 0 to 5 percent flagstones.

COMPETING SERIES: These are the Bravo, Fritsland, Huntdale, Kimper, Scaponia, and Whiteoak series. Bravo soils are 20 to 40 inches deep to bedrock. Fritsland soils are 40 to 60 inches deep to bedrock. Huntdale soils have less than 15 percent total rock fragments in the Bw horizon. Kimper and Whiteoak soils have mean annual soil temperature greater than 54 degrees F. Scaponia soils have more than 35 percent soft rock fragments in the Bw horizon.

GEOGRAPHIC SETTING: Irma soils are on metastable broad ridgetops of mountains. Slopes are 0 to 30 percent. The soils formed in colluvium and residuum derived from schist or phyllite rock types of the Colebrooke Schist Formation. Elevations are 200 to 3,000 feet. The climate is characterized by warm, wet winters and hot, moist summers. The mean annual precipitation is 90 to 130 inches. The mean annual temperature is 45 to 53 degrees F. The frost-free period is 120 to 210 days.

GEOGRAPHICALLY ASSOCIATED SOILS: These are the Barkshanty, Deadline, Edson, and Nailkeg soils. All of these soils occur on broad ridgetops, benches, or side slopes of mountains. Barkshanty and Edson soils have argillic horizons. Deadline soils are 40 to 60 inches deep to bedrock. Nailkeg soils are 20 to 40 inches deep to bedrock.

DRAINAGE AND PERMEABILITY: Well drained; moderate permeability.

USE AND VEGETATION: Irma soils are used for timber production, watershed, recreation, and wildlife habitat. The native vegetation is Douglas-fir, western hemlock, tanoak, western red cedar, Port-Orford cedar, Pacific madrone, western hazel, evergreen huckleberry, salal, western swordfern, cascade Oregongrape, common beargrass, western brackenfern, western rattlesnake plantain, western princes pine, Oregon oxalis, and evergreen violet.

DISTRIBUTION AND EXTENT: Mountainous areas of southwestern Oregon; MLRA 1. The series is not extensive.

MLRA SOIL SURVEY REGIONAL OFFICE (MO) RESPONSIBLE: Portland, Oregon

SERIES ESTABLISHED: Curry County, Oregon, 1995.

REMARKS: Diagnostic horizons and features recognized in this pedon include:

Ochric epipedon.
Humic subgroup - color requirement is met when the upper 7 inches is mixed
Cambic horizon - from a depth of 15 to 56 inches (Bw1, Bw2, and Bw3 horizons).
Particle-size control section - from 11 to 41 inches (part of the BA horizon, the Bw1, and part of the Bw2 horizon)

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National Cooperative Soil Survey
U.S.A.