LOCATION PORTHILL IDEstablished Series
TAXONOMIC CLASS: Fine, mixed, active, frigid Typic Hapludalfs
TYPICAL PEDON: Porthill silt loam, forested; on a slope of 2 percent at 2,200 feet elevation. When described on October 16, 1972, the soil was moist. The pedon was redescribed on June 15, 1998. (Colors are for dry soil unless otherwise stated.)
Oi--0 to 0.5 inch; needles and twigs. (0.5 to 1 inch thick)
Oe-0.5 to 1 inch; partly decomposed needles and twigs; trace of Mt. St. Helens volcanic ash in lower part. (0.5 to 1 inch thick)
A1--1 to 8 inches; pale brown (10YR 6/3) silt loam, dark grayish brown (10YR 4/2) moist; weak thin platy structure parting to moderate fine granular; hard, friable, slightly sticky and slightly plastic; common fine and medium roots; many very fine and fine pores; slightly acid (pH 6.2); clear wavy boundary. (3 to 7 inches thick)
A2--8 to 14 inches; pale brown (10YR 6/3) silt loam, dark grayish brown (10YR 4/2) moist; weak medium subangular blocky structure; hard, friable, slightly sticky and slightly plastic; common fine and medium roots; many very fine and fine pores; few fine black concretions; neutral (pH 6.6); clear wavy boundary. (4 to 7 inches thick)
Bt1--14 to 28 inches; light gray (2.5Y 7/2) silty clay loam, olive (5Y 5/3) moist; weak coarse prismatic structure parting to moderate medium angular blocky; extremely hard, very firm, moderately sticky and moderately plastic; common fine and medium roots; many very fine and fine pores; common faint clay films on surfaces of peds; common faint silt coatings on surfaces of peds; many fine black concretions; neutral (pH 6.6); clear wavy boundary. (11 to 20 inches thick)
Bt2--28 to 33 inches; light gray (5Y 7/2) silty clay loam, olive (5Y 5/3) moist; weak coarse prismatic structure parting to moderate medium angular blocky; very hard, firm, moderately sticky and moderately plastic; common fine and medium roots that are matted between prisms; common very fine pores; common distinct clay films on surfaces of peds; slightly alkaline (pH 7.7); gradual wavy boundary. (4 to 8 inches thick)
Bk1--33 to 44 inches; light olive gray (5Y 6/2) silty clay loam, olive gray (5Y 5/2) moist; moderate thick platy structure; very hard, firm, moderately sticky and moderately plastic; few fine roots that are matted between plates; common very fine pores; violently effervescent (calcium carbonate); many distinct lime veins and splotches; moderately alkaline (pH 8.2); clear wavy boundary. (9 to 12 inches thick)
Bk2--44 to 52 inches; light gray (5Y 7/1) silty clay loam, light olive gray (5Y 6/2) moist; moderate thick platy structure; very hard, firm, moderately sticky and moderately plastic; common very fine pores; violently effervescent (calcium carbonate); common fine faint lime veins between plates; moderately alkaline (pH 8.4); abrupt smooth boundary. (5 to 15 inches thick)
C--52 to 60 inches; light gray (5Y 7/2) silt loam, olive gray (5Y 5/2) moist; moderate thick platy structure; very hard, firm, moderately sticky and moderately plastic; violently effervescent (calcium carbonate); moderately alkaline (pH 8.4).
TYPE LOCATION: Boundary County, Idaho; about 2.5 miles south of the Canadian boundary; about 150 feet south and 2,290 feet east of the northwest corner, sec. 26, T. 65 N., R. 1 W.; Latitude - 48 degrees, 57 minutes, 46 seconds North; Longitude - 116 degrees, 25 minutes, 46 seconds West, USGS Copeland Quadrangle.
RANGE IN CHARACTERISTICS:
Average annual soil temperature - 43 to 45 degrees F.
Average summer soil temperature - 52 to 55 degrees F. with an O horizon
Moisture control section - dry 15 to 30 days (August to mid September), moist mid September through July); udic moisture regime
Thin light gray volcanic ash layer - present in some pedons in undisturbed areas between the organic and mineral soil surface
Depth to secondary calcium carbonates - 16 to 42 inches
Depth to seasonal perched water table - 12 to 18 inches (December to April)
A or Ap horizons
Hue - 10YR or 2.5Y
Value - 6 or 7 dry, 4 or 5 moist
Chroma - 2 or 3 dry or moist
Clay content - 12 to 18 percent
Reaction - moderately acid to neutral
Bt horizons
Hue - 2.5Y, 5Y, or 10YR
Value - 6 or 7 dry, 4 or 5 moist
Chroma - 2 or 3 dry or moist
Texture - SICL, SIC, SIL
Clay content - 25 to 50 percent (averages more than 35 percent)
Effervescence - none to slightly effervescent (calcium carbonate)
Calcium carbonate equivalent - 0 to 10 percent
Reaction - slightly acid to slightly alkaline
Btk horizon (present in some pedons)
Hue - 2.5Y or 5Y
Value - 6 or 7 dry, 4 or 5 moist
Chroma - 2 or 3 dry or moist
Texture - SICL, SIC, SIL
Clay content - 25 to 50 percent (averages more than 35 percent)
Calcium carbonate - lime in soft masses, seams, and hard concretions
Bk horizons
Hue - 2.5Y or 5Y
Value - 6 to 8 dry, 4 to 6 moist
Chroma - 1 to 3 dry or moist
Texture - SICL, SIL
Clay content - 25 to 35 percent
Effervescence - strongly to violently effervescent (calcium carbonate)
Calcium carbonate equivalent - 10 to 15 percent
C horizon
Hue - 2.5Y or 5Y
Value - 6 to 8 dry, 4 to 6 moist
Chroma - 1 to 3 dry or moist
Texture - SICL, SIL
Clay content - 25 to 35 percent
Effervescence - slightly to violently effervescent (calcium carbonate)
Calcium carbonate equivalent - 10 to 15 percent
COMPETING SERIES: There are no competing series.
GEOGRAPHIC SETTING: Porthill soils are on terraces. Slopes range from 0 to 20 percent. They formed in calcareous silty and clayey glaciolacustrine sediments with very minor amounts of volcanic ash in the surface. Elevations range from 2,000 to 2,400 feet. The climate is subhumid with cold wet winters and warm relatively dry summers. The average annual air temperature ranges from 42 to 45 degrees F., and the average annual precipitation is 25 to 30 inches. The average frost-free period is from 100 to 135 days.
GEOGRAPHICALLY ASSOCIATED SOILS: These are the Frycanyon (T), Rubson, and Zioncreek (T) soils. Frycanyon and Rubson soils are on terraces and are coarse-silty. Zioncreek soils are on terrace and are fine-silty.
DRAINAGE AND PERMEABILITY: Moderately well drained; medium to rapid runoff; slow permeability.
USE AND VEGETATION: More than half of the area is used for small grains, alfalfa hay, and alfalfa and clover seed production. The remainder is used for woodland, pasture, and a small acreage of Christmas trees. The natural vegetation is mainly western redcedar, grand fir, Douglas-fir, western larch, and western white pine, with an understory of myrtle pachystima, American trailplant, sweetscented bedstraw, starry false Solomons seal, queencup beadlily, baldhip rose, and longtube twinflower.
DISTRIBUTION AND EXTENT: Northern Idaho, and possibly northwestern Montana, and northeastern Washington. The series is moderately extensive.
MLRA SOIL SURVEY REGIONAL OFFICE (MO) RESPONSIBLE: Bozeman, Montana
SERIES ESTABLISHED: Boundary County, Idaho, 1974.
REMARKS:
Diagnostic horizons and features recognized in this pedon are:
Ochric epipedon - the zone from 1 to 14 inches (A1 and A2 horizons)
Argillic horizon - the zone from 14 to 33 inches (Bt1 and Bt2 horizons)
Particle-size control section - the zone from 14 to 33 inches (Bt1 and Bt2 horizons)