LOCATION IRMULCO CA
Established Series
Rev. CAR-DJE-JJJ-ET
03/2023
IRMULCO SERIES
The Irmulco series consists of deep or very deep well drained soils formed in material weathered from sandstone. Irmulco soils are on hills and have slopes of 9 to 75 percent. The mean annual precipitation is about 55 inches and the mean annual air temperature is about 53 degrees F.
TAXONOMIC CLASS: Fine-loamy, mixed, superactive, isomesic Ultic Hapludalfs
TYPICAL PEDON: Irmulco loam - on a west facing concave slope of 28 percent under redwood, Douglas-fir, tanoak, swordfern and oxalis at 650 feet elevation. (Colors are for dry soil unless otherwise stated. When described on July 12, 1979 the soil was slightly moist throughout.)
Oi--0 to 1 inch; litter of redwood and tanoak.
A--1 to 7 inches; pale brown (10YR 6/3) loam, dark brown (10YR 3/3 and 7.5YR 3/4) moist; strong very fine and fine granular structure; slightly hard, friable, nonsticky and slightly plastic; many very fine and fine roots; common fine interstitial pores; 10 percent hard subangular pebbles (2-20mm); moderately acid (pH 5.8); clear wavy boundary. (5 to 9 inches thick)
Bt1--7 to 27 inches; light brown (7.5YR 6/4) loam, brown (7.5YR 4/4) moist; moderate fine and medium subangular blocky structure; hard, firm, slightly sticky and slightly plastic; few fine and common medium roots; few fine and common very fine tubular and few very fine interstitial pores; common thin clay films on faces of peds and lining pores; 10 percent hard subangular pebbles (2-20mm), moderately acid (pH 5.6); gradual wavy boundary. (10 to 30 inches thick)
Bt2--27 to 42 inches; light brown (7.5YR 6/4) loam, brown (7.5YR 4/4) moist; moderate fine and medium subangular blocky structure; hard, firm, slightly sticky and slightly plastic; common medium and coarse and few fine roots; common very fine and few fine tubular and few very fine interstitial pores; common thin clay films on faces of peds and lining pores; many thin very pale brown (10YR 7/3) coatings, yellowish brown (10YR 5/4) moist, on faces of peds and lining pores; 4 percent hard subangular pebbles (2-20mm), strongly acid (pH 5.2); gradual wavy boundary. (10 to 20 inches thick)
Bt3--42 to 57 inches; variegated light brown (7.5YR 6/4) and pink (7.5YR 7/4) clay loam, brown (7.5YR 4/4) moist; weak medium and coarse subangular blocky structure; hard, firm, slightly sticky and plastic; common medium and coarse and few fine roots; common very fine tubular and few very fine interstitial pores; common thin clay films on faces of peds and lining pores; 9 percent hard subangular pebbles (2-20mm); strongly acid (pH 5.4); gradual wavy boundary. (10 to 20 inches thick)
Bt4--57 to 62 inches; variegated light brown (7.5YR 6/4), reddish yellow (7.5YR 6/6)and pink (7.5YR 7/4) clay loam, brown (7.5YR 4/4) and dark yellowish brown (10YR 4/4) moist; weak medium and coarse angular blocky structure; hard, firm, sticky and plastic; common medium and few fine roots; few very fine tubular and common very fine interstitial pores; many moderately thick clay films on faces of peds and common thin clay films lining pores; 2 percent hard subangular pebbles (2-20mm); strongly acid (pH 5.4); gradual wavy boundary. (0 to 10 inches thick)
Crt--62 to 73 inches; light brown (7.5YR 6/4) highly weathered sandstone; few fine and medium roots following fracture faces; continuous moderately thick clay films on fracture faces; rock slakes in water.
TYPE LOCATION: Mendocino County, California; about 3 miles south on G-P road "4000" from its intersection with Usal road; uphill 200 feet on road cut face; about 150 feet south and 2720 feet east of the northwest corner of sec. 23, T.23N., R.18W., MDBM, Hales Grove quadrangle.
RANGE IN CHARACTERISTICS: Depth to a paralithic contact and thickness of the solum is 60 to 80 inches The mean annual soil temperature ranges from 50 to 56 degrees F. The difference between mean summer and mean winter soil temperature varies from 3 to 6 degrees F. The soil between the depths of 6 and 17 inches is moist in all parts from November 1 to August 15 and is dry in some part from September 1 to October 1 in most years.
The A horizon is 10YR 3/3, 4/2, 4/3, 5/3 or 6/3. Moist color is 10YR 2/2, 3/2, 3/3, 4/3, 4/4 or 7.5YR 3/4. Gravel content is 0 to 10 percent. Reaction is moderately acid or slightly acid. Thickness for a mollic epipedon is not met.
The Bt horizon is 10YR 4/3, 4/4, 5/3, 5/4, 6/3, 6/4, 7/4; 7.5YR 6/4, 6/6 or 7/4. Moist color is 10YR 4/2, 4/3, 4/4, 5/3, 5/4, 5/6; 7.5YR 3/4, 4/4, 4/6 or 5/6. It is loam, clay loam, gravelly loam or gravelly clay loam. Clay content ranges from 20 to 40 percent. Textures with more than 35 percent clay occur below 30 inches. Gravel content is 0 to 25 percent. Reaction is very strongly through moderately acid. Base saturation (sum) is 30 to 60 percent and is greater than 35 percent in the lower part of the argillic horizon.
COMPETING SERIES: These are the
Carlain (CA) and
Tramway (CA) series. Carlain soils are very deep and have a very gravelly lithological discontinuity in the lower Bt horizon. The Tramway series is 20 to 40 inches deep to a paralithic contact.
GEOGRAPHIC SETTING: The Irmulco soils occur on mountains. Slopes are 9 to 75 percent. Elevation is 10 to 800 feet. The soils formed in material weathered from sandstone. The climate is humid with cool foggy summers and cool moist winters. A strong coastal marine influence limits the diurnal and annual range of temperature. Mean annual precipitation ranges from 40 to 70 inches. Mean January temperature is 50 degrees F.; mean July temperature is 55 degrees F.; and mean annual temperature is 53 degrees F. The frost-free season is 290 to 365 days.
GEOGRAPHICALLY ASSOCIATED SOILS: These are the competing
Carlain and
Tramway soils and the
Dehaven,
Kibesillah,
Ornbaun,
Usal,
Vandamme,
Yellowhound and
Zeni soils. All occur on hills and mountains. Kibesillah, Ornbaun, Yellowhound and Zeni soils have ustic soil moisture regimes. Dehaven, Kibesillah and Yellowhound soils are loamy-skeletal. Usal soils are mollisols. Vandamme soils have a clayey particle-size control section.
DRAINAGE AND PERMEABILITY: Well drained; surface runoff under bare soil conditions is medium to very rapid; moderate permeability.
USE AND VEGETATION: This soil is used for commercial timber, wildlife and watershed. Natural vegetation consists of redwood, Douglas-fir, tanoak, California red huckleberry, California huckleberry, swordfern, oxalis, trillium and rhododendron.
DISTRIBUTION AND EXTENT: Northern Coastal California. The series is moderately extensive. MLRA 4.
MLRA SOIL SURVEY REGIONAL OFFICE (MO) RESPONSIBLE: Davis, California
SERIES ESTABLISHED: Mendocino County, California, Western Part, 1993.
REMARKS: Diagnostic features and horizons recognized in this pedon are:
Ochric epipedon -- 0 to 6 inches (A)
Argillic horizon -- 6 to 61 inches (Bt1, Bt2, Bt3, Bt4)
Particle-size control section -- 6 to 26 inches = 20 percent clay.
Base saturation (sum) Bt4 = 36 percent.
The classification was changed in 1993 from an Ultic Tropudalf to Ultic Hapludalf. Soil Taxonomy Notice 8 deletes Tropudalfs and reclassifies them as Hapludalfs.
The activity class was added to the classification in February of 2003. Competing series were not checked at that time. - ET
Many areas mapped as Irmulco soils were mapped as Josephine soils by the California Soil Vegetation Survey 1947-1950.
ADDITIONAL DATA: NSSL number S80CA-045-008-(1-7). The Bt1 horizon was sampled as two subhorizons (6 to 15 inches and 15 to 26 inches).
National Cooperative Soil Survey
U.S.A.