LOCATION IGO                CA
Established Series


The Igo soils are very shallow and have yellowish red, strongly acid, gravelly loam Ap horizons, and yellowish red, slightly acid, gravelly heavy loam Bt horizons underlain by indurated hardpans.

TAXONOMIC CLASS: Loamy, mixed, superactive, thermic, shallow Typic Durixeralfs

TYPICAL PEDON: Igo gravelly loam - annual grass pasture - (Colors are for dry soil unless otherwise stated.)

Ap--0 to 3 inches; yellowish red (5YR 5/6) gravelly loam, dark reddish brown (5YR 3/4) moist; massive; slightly hard, friable, slightly plastic, slightly sticky; plentiful very fine roots; common micro tubular and many micro interstitial pores; strongly acid (pH 5.5); clear smooth boundary. (1 to 4 inches thick)

B2t--3 to 7 inches; yellowish red (5YR 5/6) gravelly heavy loam, dark reddish brown (5YR 3/4) moist; massive; slightly hard, friable, slightly plastic, slightly sticky; many very fine roots; many micro and common very fine interstitial and common micro tubular pores; nearly continuous clay films in most pores; slightly acid (pH 6.2); abrupt wavy boundary. (2 to 8 inches thick)

Cm--7 inches +; indurated gravelly hardpan that has intermittent thin pockets of clay in depression.

TYPE LOCATION: In Shasta County, California on Millville Plains 700 feet east of the SW corner of section 23, T31N, R3W.

RANGE IN CHARACTERISTICS: Solum thickness and depth to the duripan is 3 to 12 inches. The duripan is 20 inches thick or more. Mean annual temperature ranges from 60 to 65 degrees F., mineralogy is mixed and the soil above the duripan is dry for 60 consecutive days or more in most years. The A horizon colors are in 7.5YR and 5YR hues and have values of 4, 5 or 6 dry and 3 or 4 moist. Chromas are 4 to 8 dry and 2, 3 or 4 moist. Texture ranges from loam to gravelly or cobbly loam, gravelly clay loam and very fine sandy loam; structure from massive to moderate granular; consistence is soft to slightly hard, and reaction from strongly acid to slightly acid. The Bt horizon colors are in 5YR and 7.5YR hues with values of 4, 5 and 6 dry and 3 or 4 moist. Chromas are 4 to 6 dry and 3 or 4 moist. Texture ranges from heavy loam to light clay loam that usually is gravelly. Structure is similar to the A horizon structure; consistence is slightly hard or hard; and reaction is strongly acid to neutral.

COMPETING SERIES: These include the Cyvar and Redtough series. The Cyvar soil has hue of 10YR and a duripan at shallow depth. Redtough is shallow.

GEOGRAPHIC SETTING: The Igo soils are on gently sloping hummocky old terraces. The regolith is gravelly and cobbly alluvium derived largely from andesite, basalt and rhyolite. Elevations are 195 to 1,000 feet. The climate is sub-humid mesothermal with mean annual rainfall of 23 to 40 inches, with hot dry summers and cool moist winters. Mean annual temperature is about 63 degrees F. average January temperature about 45 degrees F., and average July temperature about 82 degrees F.

GEOGRAPHICALLY ASSOCIATED SOILS: Igo soils occur in the same general areas as the Redding and Tuscan soils; the Newtown soils on dissected terraces; and the kaolinitic Red Bluff soils.

DRAINAGE AND PERMEABILITY: Somewhat poorly drained; the duripan is nearly impermeable with water moving only through widely separated cracks. Runoff is slow to medium.

USE AND VEGETATION: Sparse annual grasses and forbs which are used for grazing.

DISTRIBUTION AND EXTENT: In Northern Sacramento Valley where the soils are inextensive.


SERIES ESTABLISHED: Shasta County, California, September, 1960.

REMARKS: The Igo series was formerly classified in the Noncalcic Brown Group.

OSED scanned by SSQA. Last revised by state on 9/66.

5/2005 Competing section updated. - SS

3/2003 Edits to cover use in Butte County. Expanded the following ranges in the A horizon: values of 6 dry; 4 moist, add clay loam, moderately acid to slightly acid. In the Bt horizon: slightly acid to neutral, clay up to 35. Expanded elevation from 400 to 195 feet and rainfall from 25 to 23 inches. Change drainage class from well to somewhat poorly. Did not review competing series.

National Cooperative Soil Survey