LOCATION SIROCO UT+ID

Established Series
Rev. RSJ/MJD/SJJ
03/2020

SIROCO SERIES

The Siroco series consists of very deep, well drained, slowly permeable soils that formed in alluvium derived from intermediate and basic igneous rocks. Siroco soils are on fan remnants and have slopes of 8 to 25 percent. The average annual precipitation is about 19 inches, and the mean annual air temperature is about 42 degrees F.

TAXONOMIC CLASS: Fine, smectitic, frigid Calcic Pachic Argixerolls

TYPICAL PEDON: Siroco cobbly loam on an 8 percent northwest facing slope, rangeland. (Colors are for dry soil unless otherwise noted.) The soil surface is covered with 10 percent cobbles and 15 percent gravel.

A--0 to 2 inches; dark grayish brown (10YR 4/2) cobbly loam, very dark grayish brown (10YR 3/2) moist; moderate thick platy structure; slightly hard, friable, slightly sticky and slightly plastic; few fine and very fine roots; many fine and very fine vesicular pores; 15 percent cobbles and 5 percent gravel; neutral (pH 7.2); clear smooth boundary.

BAt--2 to 8 inches; dark grayish brown (10YR 4/2) cobbly clay loam, dark brown (7.5YR 3/2) moist; moderate fine and very fine subangular blocky structure; hard, firm, sticky and plastic; few medium, fine and very fine roots; common fine, very fine and few medium tubular pores; few faint clay films on faces of peds; 10 percent cobbles and 5 percent gravel; slightly alkaline (pH 7.4); clear smooth boundary.

Bt1--8 to 22 inches; brown (10YR 4/3) cobbly clay, dark brown (10YR 3/3) moist; strong coarse and medium prismatic structure parting to strong medium and fine angular blocky; extremely hard, very firm, very sticky and very plastic; few medium, fine and very fine roots; common fine tubular pores; continuous prominent clay films on faces of peds; 10 percent cobbles and 5 percent gravel; slightly alkaline (pH 7.4); gradual wavy boundary.

Bt2--22 to 37 inches; brown (7.5YR 5/4) gravelly clay loam, dark brown (7.5YR 3/4) moist; moderate fine angular blocky structure; very hard, firm, sticky and plastic; few fine and very fine roots; common fine and very fine tubular pores; common faint clay films on faces of peds; 10 percent cobbles and 20 percent gravel; moderately alkaline (pH 8.2); clear wavy boundary.

Bk--37 to 60 inches; very pale brown (10YR 8/2) gravelly loam, pale brown (10YR 6/3) moist; massive; very hard, friable, slightly sticky and slightly plastic; few fine and very fine roots; common fine and very fine tubular pores; 10 percent cobbles and 15 percent gravel; violently effervescent, carbonates coatings on ped faces and on undersides of rock fragments; moderately alkaline (pH 8.4).

TYPE LOCATION: Iron County Utah; south end of Buckskin Valley in northeast corner of Iron County; 1,850 feet north and 1,850 west of the southeast corner of section 24, T.32 S., R.7 W.

RANGE IN CHARACTERISTICS: The mollic epipedon is 20 to 25 inches thick. The combined thickness of the A and Bt horizons ranges from 30 to 37 inches, overlying horizons of strong carbonate accumulation. The upper 20 inches of the Bt horizon averages 35 to 40 percent clay and 15 to 35 percent rock fragments. The mean annual soil temperature at depth of 20 inches ranges from 45 to 47 F. and the mean summer soil temperature ranges from 60 to 63 F. These soils are usually moist but are dry for 60 to 75 consecutive days in all parts of the moisture control section in more than 7 out of 10 years. The soil moisture regime is typic xeric.

The A horizon has value of 3 or 4 dry, 2 or 3 moist and chroma of 2 or 3. It has weak and moderate thin through thick platy structure that parts to weak fine through medium granular or subangular blocky structure. Rock fragments range from 5 to 25 percent. This horizon is neutral or slightly alkaline.

The BAt and Bt horizons has hue of 10YR or 7.5YR, value 4 or 5 dry, 2 to 4 moist and chroma of 2 to 4 dry and moist. It ranges from clay loam, clay or gravelly clay loam to gravelly sandy clay. Rock fragments range from 15 to 45 percent in individual layers, but averages 15 to 35 percent, mainly gravel and cobbles. Reaction is neutral or slightly alkaline

The Bk horizon has hue of 1OYR or 7.5YR, value of 6 through 8 dry, 4 through 6 moist and chroma of 1 through 4. It is gravelly loam, gravelly clay loam, very gravelly sandy loam, very gravelly loamy coarse sand or loam in individual layers. Rock fragments range from 10 to 60 percent.

COMPETING SERIES: This is the Iwica series. Iwica soils are 40 to 60 inches deep to a duripan.

GEOGRAPHIC SETTING: Siroco soils are at elevations of 7,100 to 7,800 feet. They occur on north-facing, convex-concave fan remnants. Slopes range from 8 to 25 percent. These soils formed in alluvium derived from intermediate and basic igneous rocks. The climate is moist subhumid and average annual precipitation ranges from 16 to 22 inches. The mean annual temperature ranges from 39 to 45 F. and the mean summer temperature ranges from 60 to 64 F. The frost-free period ranges from 75 to 100 days.

GEOGRAPHICALLY ASSOCIATED SOILS: These are the Doyce, Rob Roy, and Tolman soils. Doyce soils have a mean annual soil temperature of 47 degrees F. or more and have less than 35 percent clay in the Bt horizon. Rob Roy soils have bedrock at a depth of 20 inches or less. Tolman soils are 20 to 30 inches deep over bedrock.

DRAINAGE AND PERMEABILITY: Well drained; slow runoff; slow permeability.

USE AND VEGETATION: These soils are used for rangeland and wildlife habitat. Principal native vegetation is mountain big sagebrush, Gambel oak, antelope bitterbrush, mountain snowberry, Utah serviceberry, lupine, prickly pear, bottlebrush squirreltail, western wheatgrass, prairie junegrass, Sandberg bluegrass and needleandthread.

DISTRIBUTION AND EXTENT: Southern Utah. MLRA 47B. This series is inextensive.

MLRA SOIL SURVEY REGIONAL OFFICE (MO) RESPONSIBLE: Bozeman, Montana

SERIES ESTABLISHED: Iron County, Utah, Iron-Washington Soil Survey Area, 1997.

REMARKS: Diagnostic horizons and features recognized in this pedon are:
Mollic epipedon (Pachic feature)- the zone from the surface of the soil to a depth 22 inches.
Argillic horizon - the zone of clay accumulation from 2 to 37 inches.
Calcic horizon - the zone of secondary carbonate accumulation from 37 to 60 inches.

Keys to Soil Taxonomy: Series classified according to Eighth Edition, 1998.

The series concept for parent material source is being narrowed to igneous rocks. The reference to minor influence from sedimentary rocks was removed. February 2000.

ADDITIONAL DATA:

National Cooperative Soil Survey
U.S.A.