LOCATION BENHAM WAEstablished Series
TAXONOMIC CLASS: Pumiceous or ashy-pumiceous over medial, glassy over amorphic, frigid Typic Udivitrands
TYPICAL PEDON: Benham paragravelly sandy loam - under a coniferous forest on a 25 percent convex east facing back slope at an elevation of 2,440 feet. (The soil was moist when described. Colors are for moist soil unless otherwise stated. All textures are apparent field textures.)
Oe--4.5 inches to 0; loose, partially decomposed organic litter, composed of needles, leaves, twigs, cones, bark chips, wood and roots; abrupt smooth boundary. (1 to 6 inches thick)
E--0 to 3 inches; dark gray (10YR 4/1) sandy loam, gray (10YR 6/1) dry; weak fine subangular blocky structure; slightly hard, very friable, nonsticky, nonplastic and weakly smeary; many very fine,fine, medium and coarse roots; 5 percent subangular pumice fragments (2-10 mm in diameter); slightly acid (pH 6.2); abrupt wavy boundary. (0.5 to 3 inches thick)
Bw--3 to 9 inches; dark grayish brown (10YR 4/2) paragravelly sandy loam, light brownish gray (10YR 6/2) dry;many medium prominent dark brown (7.5YR 3/4) mottles, brown (7.5YR 5/4) dry; weak fine subangular blocky structure; slightly hard, very friable, nonsticky, nonplastic and weakly smeary; many very fine, fine, medium and coarse roots; common fine pores; 15 percent subangular pumice fragments (2-10 mm in diameter); moderately acid (pH 6.0); abrupt wavy boundary. (4 to 8 inches thick)
2BC--9 to 13 inches; white (10YR 8/1) and reddish yellow (7.5YR 6/8) very paragravelly loamy sand, white (10YR 8/1) and reddish yellow (7.5YR 7/6) dry; single grain; loose; common very fine, fine, medium and coarse roots; 45 percent subangular pumice fragments (2-10 mm in diameter); slightly acid (pH 6.2); clear wavy boundary. (3 to 6 inches thick)
2C--13 to 27 inches; white (10YR 8/1) and reddish yellow (7.5YR 7/6) very paragravelly sand, white (10YR 8/1) and reddish yellow (7.5YR 8/6) dry; single grain; loose; few very fine and fine roots; 55 percent subangular pumice fragments (2-20 mm in diameter); slightly acid (pH 6.4); abrupt wavy boundary. (12 to 20 inches thick)
3Bsb1--27 to 31 inches; dark gray (10YR 4/1) paragravelly sandy loam; gray (l0YR 6/l) dry; many fine prominent yellowish red (5YR 4/6) mottles, yellowish red (5YR 5/6) and reddish yellow (7.5YR 6/6) dry;weak fine subangular blocky structure; slightly hard, very friable, nonsticky, nonplastic and weakly smeary; common very fine, fine, medium, and coarse roots; common fine pores; 20 percent subangular pumice fragments (2-20 mm in diameter); slightly acid (pH 6.2); clear wavy boundary. (3 to 6 inches thick)
3Bsb2--31 to 40 inches; gray (10YR 6/1) paragravelly sandy loam, light gray (10YR 7/1) dry; many fine and medium prominent yellowish red (5YR 4/6) mottles, reddish yellow (5YR 6/6) dry; weak fine subangular blocky structure; slightly hard, very friable, nonsticky, nonplastic and weakly smeary; common very fine, fine, medium and coarse roots; common fine pores; 20 percent subangular pumice fragments (2-20 mm in diameter); slightly acid (pH 6.2); abrupt wavy boundary. (8 to 20 inches thick)
4Bsb3--40 to 44 inches; strong brown (7.5YR 5/8) very paragravelly loamy sand, reddish yellow (7.5YR 7/6) dry; single grain; loose, common very fine, fine and medium roots; 55 percent subangular pumice fragments (2 mm to 5 cm in diameter); slightly acid (pH 6.2); clear wavy boundary. (4 to 6 inches thick)
4Bsb4--44 to 61 inches; reddish yellow (7.5YR 7/6 and 7.5YR 6/8) extremely paragravelly sand, reddish yellow (7.5YR 8/6 and 7.5YR 7/8) dry; single grain; loose; 70 percent subangular pebble-size pumice fragments and a few cobble-size fragments (3 - 6 inches in diameter); slightly acid (pH 6.4). (10 to 24 inches thick)
TYPE LOCATION: Lewis County, Washington; near an unpaved U.S. Forest Service road, 1,200 feet south and 620 feet west of the northeast corner, sec. 36, T. 11 N., R. 6 E., W.M.
RANGE IN CHARACTERISTICS: These soils are dry less than 45 consecutive days in most years. Depth to bedrock is 40 to 60 inches or more. Mean annual soil temperature at a depth of 20 inches ranges from 44 to 46 degrees F. Depth to the buried profile ranges from 20 to 35 inches. Reaction ranges from moderately acid to slightly acid throughout. The particle-size control sectin is ashy over ashy-pumiceous over medial. The ashy and ashy-pumiceous parts are estimated to have 3 to 10 percent 15-bar moisture (dry). The soil is 60 percent or more by weight vitric volcanic ash and pumiceous cinders.
The E horizon has hue of 10YR or 2.5Y, value of 4 or 5 moist, 6 to 8 dry, and chroma of 0 to 2 moist and dry. It has 5 to 60 percent pebble-size pumice fragments.
The Bw horizon has value of 4 or 5 moist, 6 or 7 dry, and chroma of 2 or 3 moist and dry. It has fine and medium mottles with hue of 10YR through 5YR, value of 3 or 4 moist, 5 to 7 dry, and chroma of 4 to 6 moist and dry. This horizon has 15 to 30 percent pebble-size pumice fragments.
The 2BC and 2C horizons have hue of 10YR or 7.5YR, value of 6 to 8 moist, 7 or 8 dry and chroma of 1 to 8 moist and dry. It has 45 to 75 percent pebble-size pumice fragments.
The 3Bsb1 horizon has hue of 10YR through 5YR, value of 4 to 6 moist, 6 to 8 dry, and chroma of 1 to 3 moist and dry. It has fine or medium mottles with hue of 10YR through 5YR, value of 3 to 6 moist, 5 to 7 dry, and chroma of 4 to 8 moist and dry. This horizon has 5 to 25 percent pebble-size pumice fragments.
An intermittent 3Eb horizon tongues into the 3Bsb in some pedons.
The 4Bsb horizon has hue of 10YR through 5YR, value of 5 to 7 moist, 6 to 8 dry, and chroma of 2 to 8 moist and dry. It has 40 to 80 percent pebble and cobble-size pumice fragments, and 0 to 20 percent hard pebbles.
COMPETING SERIES: There are no competing series. The Bannel soils are similar. Bannel soils have ashy-pumiceous layers 5 to 7 inches thick which constitute the upper part of the particle-size control section ("W" tephra set), and do not have an E horizon at the soil surface.
GEOGRAPHIC SETTING: Benham soils are on mountain slopes at elevation of 1,800 to 2,800 feet. Slopes are 0 to 90 percent. These soils formed in layers of aerially deposited dacitic pumice and volcanic ash from Mt. St. Helens. Beginning at the surface of the mineral soil, the stratigraphy of Mt. St. Helens pyroclastic material in Benham soil profiles is (1) "Layer T" ash and pumice about 176-years old, (2) "Layer W" pumice of about 300-year age, (3) "Layer P" ash and pumice of undefined age, and (4) "Layer Y" pumice of about 3,200-year age. The climate is characterized by cool, dry summer and cool, wet winters. Mean annual precipitation is 70 to 90 inches including snowfall. Mean annual temperature is 42 to 44 degrees F. Growing season (28 degrees F) is 150 to 180 days.
GEOGRAPHICALLY ASSOCIATED SOILS: These are the competing Bellicum, Bromo, and Colter soils and the Cispus, Hoffstadt and Nevat soils. Cispus soils are cindery and have a mesic temperature regime. Hoffstadt soils are medial-skeletal. Nevat soils have a mesic temperature regime.
DRAINAGE AND PERMEABILITY: Well drained; slow to medium runoff; moderately rapid permeability in the upper part of the control section, rapid in the lower part of the cindery layer, moderately rapid in the upper part of the buried subsoil and very rapid in the lower part.
USE AND VEGETATION: Overstory vegetation is western hemlock, Douglas-fir, and western redcedar, ground vegetation is tree seedlings, Oregon-grape, salal, creambush oceanspray, red huckleberry, trailing blackberry, western swordfern and western brackenfern.
DISTRIBUTION AND EXTENT: Mountain slopes of the Cascade Range in southeastern Lewis and Northern Skamania Counties, Washington, north and northeast of Mt. St. Helens. The series is of small extent.
MLRA SOIL SURVEY REGIONAL OFFICE (MO) RESPONSIBLE: Portland, Oregon
SERIES ESTABLISHED: Lewis County, Washington, 1979.
REMARKS:
Diagnostic horizons and features recognized in this are:
ochric epipedon from the mineral surface to 3 inches, and a buried cambic horizon from 27 to 40 inches. The particle-size control section is from the mineral soil surface to 40 inches and qualifies as a contrasting particle-size class. From 9 to 27 inches qualifies as ashy-pumiceous and from 27 to 40 inches qualifies as medial. More investigation is needed to confirm the medial classificaiton of the "P" tephra set.
Classification changed 6/98 based on Keys to Soil Taxonomy.