LOCATION GIBBS WATentative Series
TAXONOMIC CLASS: Fine-loamy, isotic, mesic Vitrandic Argixerolls
TYPICAL PEDON: Gibbs ashy silt loam, on an east-facing slope of 4 percent at an elevation of 2,500 feet under ponderosa pine canopy. When described on October 4, 2000, the soil was dry throughout. (Colors are for dry soil unless otherwise noted. All textures are apparent field textures)
Oi--0 to 0.5 inches; slightly decomposed needles, twigs and leaves.
Oe--0.5 to 1 inches; moderately decomposed organic matter mixed with Mt. St. Helen's ash from 1980.
A--1 to 5 inches; brown (10YR 4/3) ashy silt loam, very dark grayish brown (10YR 3/2) moist; weak fine and medium subangular blocky structure; slightly hard, friable, slightly sticky and slightly plastic; common very fine, fine, and few medium roots; many very fine and fine tubular and many fine irregular pores; neutral (pH 6.8); clear wavy boundary. (2 to 6 inches thick)
AB--5 to 13 inches; dark grayish brown (10YR 4/2) ashy silt loam, very dark grayish brown (10YR 3/2) moist; moderate coarse subangular blocky structure; hard, firm, slightly sticky and slightly plastic; common very fine, fine, and few medium roots; common very fine and fine tubular pores; neutral (pH 7.0); clear wavy boundary. (5 to 8 inches thick)
Bt1--13 to 20 inches; brown (10YR 5/3) silty clay loam, dark brown (10YR 3/3) moist; moderate coarse subangular blocky structure; very hard, firm, slightly sticky and moderately plastic; common very fine, fine, and medium roots; common very fine and few fine tubular pores; 10 percent faint clay films on all faces of peds; 2 percent subrounded basalt gravel; slightly acid (pH 6.2); gradual wavy boundary. (5 to 8 inches thick)
Bt2--20 to 31 inches; yellowish brown (10YR 5/4) silty clay loam, dark yellowish brown (10YR 3/4) moist; moderate medium and coarse subangular blocky structure; very hard, firm, slightly sticky and moderately plastic; few fine roots throughout and few medium roots throughout and few very fine roots throughout; common very fine and few fine tubular pores; 25 percent faint clay films on all faces of peds; 5 percent subrounded basalt gravel; neutral (pH 6.6); clear wavy boundary. (10 to 16 inches thick)
BCt--31 to 35 inches; yellowish brown (10YR 5/4) very cobbly silt loam, dark yellowish brown (10YR 3/4) moist; weak medium subangular blocky structure; very hard, very firm, slightly sticky and moderately plastic; few very fine, fine, and medium roots; few very fine and fine tubular pores; 20 percent faint clay films on all faces of peds; 30 percent subangular basalt cobbles and 20 percent angular basalt cobbles; neutral (pH 6.7); abrupt wavy boundary. (2 to 4 inches thick)
2R--35 inches; indurated basalt bedrock, fractured at intervals of 4-18 inches; weathering rinds in fractures about 1 inch thick.
TYPE LOCATION: Spokane County, Washington; about 1.25 miles southwest of Mica, about 800 feet west and 1,960 feet south of the northeast corner of Section 28, Township 24N, Range 44E. USGS Freeman, Wash. Topographic quadrangle; (Latitude 47 degrees, minutes, seconds N. and Longitude 117 degrees, minutes, seconds W.), NAD83
RANGE IN CHARACTERISTICS: Depth to diagnostic horizons and features are measured from the top of the first mineral layer.
Mean annual soil temperature - 48 to 52 degrees F.
Moisture control section - dry 60 to 90 days after the summer solstice, July to September, moist October through June
Depth to basalt bedrock - 20 to 40 inches
Thickness of mollic epipedon - 10 to 20 inches
Field estimated clay content - 18 to 30 percent in the particle-size control section
Reaction - slightly acid to neutral
Volcanic ash influence - 7 to 14 inches
Estimated properties of the volcanic ash influenced layers
Volcanic glass content in the 0.02 to 2 mm fraction - 5 to 20 percent
Acid-oxalate extractable Al plus 1/2 Fe - 0.4 to 1.0 percent
Moist bulk density - 1.15 to 1.35 g/cc
15 bar water retention - 5 to 10 percent for air dried samples
Base Saturation - less than 75 percent (by sum of cations) in one or more horizon between 10 and 30 inches (estimated)
A horizon
Value - 4 or 5 dry, 2 or 3 moist
Chroma - 2 or 3 dry or moist
Gravel content - 0 to 5 percent
AB horizon
Value - 4 or 5 dry, 2 or 3 moist
Chroma - 2 or 3 dry or moist
Texture - ashy silt loam or ashy loam
Gravel content - 0 to 5 percent
Bt horizons
Value - 5 or 6 dry, 3 or 4 moist
Chroma - 3 to 6 dry or moist
Texture - silt loam, loam, or silty clay loam
Clay content - 18 to 30 percent
Gravel content - 0 to 10 percent
2BCt horizon (or 2C horizon when present)
Hue - 10YR or 7.5YR
Value - 5 or 6 dry, 3 or 4 moist
Chroma - 4 to 6 dry or moist
Texture - silt loam, loam, or silty clay loam
Rock fragment content - 30 to 75 percent total
Gravel content - 30 to 60 percent
Cobble content - 0 to 20 percent
COMPETING SERIES: These are the Dragoon and Glenrose series. Soils with a similar classification with mixed mineralogy are the Georgecreek, Hillcreek (T), Morical, Mozen (T), Pachneum (T), Ralock (T), Rollinger, Shushuskin (T), Teewee, Tolius, Umperon (T), Vanderbilt (T), Vollinger (T), Wenner (T), and Wockum (T) series. Dragoon and Morical soils are 20 to 40 inches deep to a paralithic contact. Glenrose, Pachneum, Umperon, Vanderbilt, and Wenner soils are very deep. Georgecreek soils are 40 to 60 inches to paralithic contact. Hillcreek soils have mollic epipedons 20 to 45 inches thick and are very deep. Mozen soils have mollic epipedons that are 20 to 35 inches thick, are dry for 90 to 100 days after the summer solstice, and have secondary carbonates in the argillic horizon. Shushuskin soils have mollic epipedons that are 20 to 35 inches thick. Ralock soils are very deep and have secondary carbonates at a depth of 22 to 38 inches. Teewee soils have 10 to 25 percent medium, coarse, and very coarse sand and are 40 to 60 inches to weathered andesite bedrock. Rollinger and Tolius soils are very deep. Vollinger soils are very deep and have secondary carbonates at a depth of 43 to 60 inches. Wockum soils are very deep and are dry for 90 to 100 consecutive days.
GEOGRAPHIC SETTING: Gibbs soils are on basalt plateaus and terraces. Slopes are 0 to 15 percent. These soils formed in colluvium and residuum weathered from basalt with minor amounts of glaciofluvial deposits, loess, and volcanic ash in the upper part. Elevations are 2,350 to 2,700 feet. The climate is characterized by warm, relatively dry summers and cool, moist winters. The mean annual precipitation is 18 to 25 inches. The mean annual air temperature is 46 to 50 degrees F. The frost-free season is 100 to 130 days.
GEOGRAPHICALLY ASSOCIATED SOILS: These are the Bobbitt, Driscoll, Lacy, and Uhlig soils Bobbitt soils are loamy-skeletal and are on basalt plains. Driscoll soils are fine and are on loess hills. Lacy soils are shallow to basalt, are loamy-skeletal, and are on basalt ridges and terraces. Uhlig soils are coarse-loamy and are on basalt plateaus.
DRAINAGE AND PERMEABILITY: Well drained; moderately slow permeability.
USE AND VEGETATION: These soils are used mostly for homesites, grazeable woodland, crop production, with some areas used for wildlife habitat and watershed. Small grains, hay and pasture, are common crops. Potential natural vegetation is ponderosa pine, Saskatoon serviceberry, common snowberry, Idaho fescue, arrowleaf balsamroot, common yarrow, and lupine.
DISTRIBUTION AND EXTENT: Eastern Washington; MLRA 9, 44. Series is of small extent.
MLRA OFFICE RESPONSIBLE: Portland, Oregon
SERIES PROPOSED: Spokane County, Washington, 2001.
REMARKS: Diagnostic horizons and features recognized in this pedon are:
Mollic epipedon - the zone from 1 to 20 inches (A, AB, and Bt1 horizons)
Argillic horizon - the zone from 13 to 31 inches (Bt1 and Bt2 horizons)
Vitrandic feature - the zone from 1 to 13 inches (A and AB horizons)
Ultic feature - the zone from 11 to 31 inches having base saturation by sum of cations of less than 75 percent in one or more horizon
Particle-size control section - the zone from 13 to 31 inches (Bt horizons)
This series is correlated to the PIPO/SYAL habitat type.