LOCATION ISOM                    UT

Established Series
Rev. KMD/RSJ/MJD/WWJ
04/2015

ISOM SERIES

The Isom series consists of very deep, well drained soils that formed in alluvium from limestone, sandstone and shale. The Isom soils are on alluvial fans. Slope ranges from 3 to 30 percent. The mean annual air temperature is about 61 degrees F., and the mean annual precipitation is about 9 inches.

TAXONOMIC CLASS: Loamy-skeletal, carbonatic, thermic Typic Torriorthents

TYPICAL PEDON: Isom very cobbly sandy loam - rangeland (Colors are for air dry soil unless otherwise noted.)

A--0 to 2 inches; brown (7.5YR 5/4) very cobbly sandy loam, brown (7.5YR 4/4) moist; weak very fine granular structure; soft, very friable, slightly sticky, nonplastic; 40 percent cobbles and gravel; strongly effervescent, carbonates are disseminated; moderately alkaline (pH 8.4); clear smooth boundary. (2 to 5 inches thick)

C1--2 to 10 inches; light brown (7.5YR 6/4) very cobbly sandy loam, brown (7.5YR 4/4) moist; massive; soft, very friable, slightly sticky, nonplastic; 40 percent cobbles and gravel; strongly effervescent, carbonates are disseminated; moderately alkaline (pH 8.4); clear wavy boundary. (8 to 13 inches thick)

C2--10 to 22 inches; light brown (7.5YR 6/4) very cobbly sandy loam, brown (7.5YR 5/4) moist; massive; soft, very friable, slightly sticky, nonplastic; about 55 percent cobbles and pebbles; thin coating of gypsum occurs on many cobble and gravel; strongly effervescent, carbonates are disseminated; moderately alkaline (pH 8.2); gradual wavy boundary. (12 to 13 inches thick)

Cy--22 to 60 inches; pink (7.5YR 7/4) extremely cobbly sandy loam, light brown (7.5YR 6/4) moist; single grained; loose, very friable; about 65 percent cobbles and gravel; thin coating of gypsum occur on most cobbles and pebbles; strongly effervescent, carbonates are disseminated; moderately alkaline (pH 8.0).

TYPE LOCATION: Washington County, Utah; 8 3/4 miles south of Hurricane; about 1,140 feet south and 1,000 feet east of the northwest corner of sec. 15, T.43S., R.13W; The Divide Quadrangle; lat. 37 degrees 3 minutes 3 seconds N. and long. 113 degrees 18 minutes 23 seconds W.

RANGE IN CHARACTERISTICS:

Soil moisture - Intermittently moist in some part of the soil moisture control section during July-September and December-February. Driest during May and June. Typic aridic soil moisture regime.

The soil is 40 to 60 inches or more deep

Mean annual soil temperature: 59 to 67 degrees F.

Mean summer soil temperature: 78 to 83 degrees F.

Rock fragments: 35 to 80 percent cobble and gravel

Reaction: moderately or strongly alkaline

Calcium carbonate equivalent(including lime in rock fragments less than 20 mm. in diameter): 40 to 60 percent

A horizon
Value: 5 or 6 dry and 4 or 5 moist
Texture: cobbly sandy loam or gravelly sandy loam to very cobbly fine sandy loam

C horizon
Hue: 7.5YR or 5YR
Value: 5 through 7 dry, 4 through 6 moist
Chroma: 3 through 5
Texture: very cobbly fine sandy loam to extremely gravelly coarse sandy loam and is commonly stratified with layers of very gravelly loam and very gravelly sand
Gypsum content: 1 to 5 percent in the lower part of the C horizon.

COMPETING SERIES: These are the Dalian and Threelakes series. Dalian soils lack gypsum in the profile. Threelakes soils are in the Mohave Desert (MLRA 30), receive mostly winter precipitation and are usually dry from April through November.

GEOGRAPHIC SETTING: Isom soils are on alluvial fans at elevations of 2,700 to 3,900 feet. Slopes are 3 to 30 percent. These soils formed in alluvium from limestone, sandstone and shale. The mean annual temperature is 57 to 65 degrees F., and the mean summer temperature is 79 to 84 degrees F. The average annual precipitation is 8 to 11 inches. Frost-free period is 175 to 195 days.

GEOGRAPHICALLY ASSOCIATED SOILS: These are the Junction, Leeds, and Tobler. Junction, Leeds, and Tobler soils lack rock fragments in the control section.

DRAINAGE AND PERMEABILITY: Well-drained; medium runoff; moderately rapid permeability.

USE AND VEGETATION: Used as rangeland. Vegetation is creosotebush, Mormon tea, cholla, and cheatgrass.

DISTRIBUTION AND EXTENT: Southern Utah and northern Arizona. This soil occurs in LRR-D, MLRA 30. The series is inextensive.

MLRA SOIL SURVEY REGIONAL OFFICE (MO) RESPONSIBLE: PHOENIX, ARIZONA

SERIES ESTABLISHED: Virgin River Valley Area, Utah, 1942

REMARKS: Diagnostic horizons and features in this pedon include:

Ochric epipedon - from a depth of 0 to 2 inches (A horizon)

Entisol feature - The absence of diagnostic subsurface horizons

Classified according to Soil Taxonomy Second Edition, 1999.

When the competing series section was updated in September 2001, questions were raised about the description and/or the classification of this series. A field study of the type location is recommended to resolve the questions.

Responsibility for this series was transferred from Davis to Phoenix 4/2015. The last revision to the series was 6/2012. ET

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National Cooperative Soil Survey
U.S.A.