LOCATION FOURMOUND WATentative Series
TAXONOMIC CLASS: Coarse-loamy, isotic, mesic Vitrandic Haploxerolls
TYPICAL PEDON: Fourmound gravelly ashy silt loam, on a northwest, convex slope at an elevation of 2,420 feet in a ponderosa pine forest. When described on August 10, 2000 the soil was dry to 43 inches and slightly moist below. (Colors are for dry soil unless otherwise noted. All textures are apparent field textures)
A1--0 to 4 inches; brown (10YR 4/3) gravelly ashy silt loam, very dark grayish brown (10YR 3/2) moist; strong fine and medium granular structure; soft, very friable, slightly sticky and slightly plastic; many very fine, few fine, and few medium roots; many very fine, fine, and medium irregular pores; 15 percent subangular basalt gravel; slightly acid (pH 6.5); diffuse smooth boundary.
A2--4 to 9 inches; brown (10YR 5/3) ashy silt loam, very dark grayish brown (10YR 3/2) moist; weak fine and medium subangular blocky structure; soft, very friable, slightly sticky and slightly plastic; many very fine, few fine, few medium roots; many very fine irregular and few fine tubular pores; 10 percent subangular basalt gravel; slightly acid (pH 6.4); gradual smooth boundary.
A3--9 to 15 inches; yellowish brown (10YR 5/4) ashy silt loam, dark brown (10YR 3/3), moist; weak fine and medium subangular blocky structure; slightly hard, very friable, slightly sticky and slightly plastic; common very fine, and few fine, medium, and coarse roots; many very fine irregular, few fine tubular and few medium tubular pores; 10 percent subangular basalt gravel; slightly acid (pH 6.2); gradual wavy boundary. (combined thickness of the A horizon is 10 to 20 inches thick)
2Bw1--15 to 30 inches; yellowish brown (10YR 5/4) silt loam, brown (10YR 4/3) moist; weak fine and medium subangular blocky structure; slightly hard, very friable, slightly sticky and slightly plastic; few very fine, few fine, common medium, and few coarse roots; many very fine irregular and few fine and medium tubular pores; 10 percent subangular basalt gravel; slightly acid (pH 6.1); gradual wavy boundary.
2Bw2--30 to 43 inches; light yellowish brown (10YR 6/4) silt loam, dark yellowish brown (10YR 4/4) moist; weak fine and medium subangular blocky structure; moderately hard, friable, slightly sticky and slightly plastic; few very fine, fine , medium and coarse roots; many very fine irregular, few very fine and fine tubular pores; 2 percent patchy faint organic stains; 10 percent subangular basalt gravel; moderately acid (pH 5.8); diffuse wavy boundary. (combined thickness of the 2Bw horizon is 20 to 30 inches thick)
2BC--43 to 47 inches; light yellowish brown (10YR 6/4) extremely gravelly silt loam, yellowish brown (10YR 5/4) moist; weak fine subangular blocky structure; slightly hard, very friable, nonsticky and nonplastic; few very fine, and common fine roots matted around gravel; many very fine irregular and few fine tubular pores; 70 percent subangular basalt gravel; moderately acid (pH 5.8); diffuse wavy boundary. (0 to 5 inches thick)
2R--47 inches; unweathered basalt bedrock.
TYPE LOCATION: Spokane County, Washington About 1,700 feet south and 700 feet east of Section 16, Township 26N, Range 41E., W.M.; USGS Four Mound Prairie, Wash. Topographic quadrangle; (Latitude 47 degrees, 45 minutes, 15.9 seconds N. and Longitude 117 degrees, 38 minutes, 38.6 seconds W.), NAD83
RANGE IN CHARACTERISTICS: Depths to diagnostic horizons and features are measured from the top of the first mineral layer.
Average 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 - 40 to 60 inches
Thickness of mollic epipedon - 10 to 20 inches
Clay content - 4 to 18 percent in the particle-size control section
Gravel content - 0 to 20 percent in particle size control section
Reaction - Moderately or slightly acid
Volcanic ash influence - 10 to 20 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)
O horizon present in some pedons
A horizons
Value - 4 or 5 dry, 2 or 3 moist
Chroma - 1 to 3 moist, 3 or 4 dry
Texture - ashy silt loam or ashy silt loam
Clay content - 4 to 18 percent
Gravel content - 0 to 20 percent
2Bw horizons
Hue - 10YR or 2.5Y
Value - 5 or 6 dry, 4 or 5 moist
Chroma - 3 or 4 dry or moist
Texture - loam or silt loam
Clay content - 4 to 18 percent
Gravel content - 0 to 20 percent
2BC horizons (when present)
Hue - 10YR or 2.5YR
Value - 5 or 6 dry, 4 or 5 moist
Chroma - 3 or 4 dry or moist
Texture - loam or silt loam
Clay content - 5 to 15 percent
Gravel content - 35 to 80 percent
Cobble content - 0 to 20 percent
In some pedons the 2BC or 2C horizons also contain mixed glacial flood gravels.
COMPETING SERIES: These are the Conconully, Deno (T), Donovan (T), Fanal (T), Gibbs, (T), Goldlake, Phoebe, Safety, Spokane, Stevens, Uhlig and Usk soils. Deno (T) soils are pahic. Conconully, Donovan, and Stevens soils are moderately deep to Cd horizons. Fanal and Goldlake soils are moderately well drained with redox concentrations in the lower part of the control section. Gibbs soils have a lithic contact at 20 to 40 inches. Phoebe and Uhlig soils are very deep. Safety, Spokane, and Usk soils have a paralithic contact at 20 to 40 inches.
GEOGRAPHIC SETTING: Fourmound soils are on outwash plains, outwash terraces and mima mounds on basalt plateaus in the Channeled Scablands. Slopes are 0 to 15 percent. These soils formed over basalt in glaciofluvial deposits mixed with loess and volcanic ash in the upper part. Elevations are 1,800 to 2,600 feet. The climate is characterized by warm, relatively dry summers and cool, moist winters. The average annual temperature is 46 to 50. The average annual precipitation is 15 to 20 inches. The frost-free period is 100 to 130 days.
GEOGRAPHICALLY ASSOCIATED SOILS: These are the Alecanyon, Cheney, Gibbs (T), Northstar, Rockly, and Stutler (T) soils. Alecanyon soils are sandy skeletal and are on outwash plains. Cheney soils are coarse-loamy over sandy or sandy-skeletal and are on outwash plains. Gibbs soils are moderately deep to bedrock and are on outwash plains and basalt plateaus. Rockly soils are shallow to bedrock and are on outwash plains and basalt plateaus. Northstar soils are loamy skeletal, moderately deep to basalt bedrock, and are on basalt plateaus. Stutler soils are loamy skeletal and are on outwash plains and basalt plateaus.
DRAINAGE AND PERMEABILITY: Well drained; moderate permeability.
USE AND VEGETATION: These soils are used mostly for homesites, crop production, grazeable woodland with some areas used for wildlife habitat and watershed. Small grains, hay and pasture are common crops. Potential natural vegetation is ponderosa pine, Idaho fescue, bluebunch wheatgrass, Sandberg bluegrass, Wyeth eriogonum, arrowleaf balsamroot, common yarrow, lupine, common snowberry, common chokecherry, Saskatoon serviceberry, rose, and pinegrass.
DISTRIBUTION AND EXTENT: Eastern Washington; MLRA B9. 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 0 to 15 inches (A and AB horizons)
Cambic horizon - the zone from 15 to 43 inches (2Bw horizons)
Vitrandic feature - the zone from 0 to 15 inches (A horizons)
Lithic contact - the zone beginning at 47 inches (2R horizon)
Particle-size control section - the zone from 10 to 40 inches (A horizons, the 2 Bw1 horizon and part of the 2Bw2 horizon)
The discontinuity in the 2Bw1 horizon represents the limit of the vitrandic feature and the influence of air-fall volcanic ash. This Fourmound pedon (00WA063002) has been sent to NSSL for characterization.
This series is correlated to a PIPO/SYAL habitat type.