LOCATION VANWIRT COEstablished Series
TAXONOMIC CLASS: Loamy-skeletal, mixed, superactive Ustic Haplocryolls
TYPICAL PEDON: Vanwirt gravelly loam, on an east facing 32 percent mountain slope under quaking aspen at an elevation of 10,220 feet. (colors are for dry soil unless otherwise noted.
Oi--0 to 2 inches; mat of slightly decomposed grasses, twigs, and leaves (0 to 2 inches thick)
A1--2 to 10 inches; very dark grayish brown (10YR 3/2) gravelly loam, black (10YR 2/1) moist; moderate fine granular structure parting to weak fine subangular blocky; soft, very friable, nonsticky and nonplastic; 20 percent gravel; neutral (pH 6.8); clear wavy boundary.
A2--10 to 16 inches; brown (10YR 5/3) very gravelly loam, very dark grayish brown (10YR 3/2) moist; weak fine and medium subangular blocky structure; slightly hard, friable, nonsticky and slightly plastic; 25 percent gravel, 10 percent cobbles; neutral (pH 6.8); clear wavy boundary. (combined thickness of the A horizons is 10 to 15 inches)
Bt1--16 to 29 inches; pale brown (10YR 6/3) very gravelly sandy clay loam, brown (10YR 4/3) moist; weak fine and medium subangular blocky structure; slightly hard, friable, slightly sticky and slightly plastic; few faint clay films on faces of peds and as bridges; 30 percent gravel, 10 percent cobbles; neutral (pH 6.8); clear smooth boundary.
Bt2--29 to 42 inches; light yellowish brown (10YR 6/4) very gravelly sandy clay loam, dark yellowish brown (10YR 4/4) moist; moderate fine and medium subangular blocky structure; hard, friable, slightly sticky and slightly plastic; few faint clay films on faces of peds and as bridges; 35 percent gravel, 10 percent cobbles; neutral (pH 6.8); gradual smooth boundary.
Bt3--42 to 66 inches; yellowish brown (10YR 5/4) very gravelly sandy clay loam, dark brown (10YR 3/3) moist; weak fine subangular blocky structure; hard, friable, slightly sticky and slightly plastic; common faint clay films on faces of peds and as bridges; 40 percent gravel, 10 percent cobbles; neutral (pH 6.6). (combined thickness of the Bt horizons is 20 to 50 inches)
TYPE LOCATION: Gunnison County, Colorado; about 2 miles south of Pitkin, Colorado; located about 1,400 feet east and 1,750 feet north of the southwest corner of Section 22, T. 50 N., R. 4 E.; USGS Pitkin topographic quadrangle; latitude 38 degrees, 34 minutes, 33 seconds north and longitude 106 degrees, 30 minutes, 38 seconds west, NAD 1927.
RANGE IN CHARACTERISTICS: Depths in this section are measured from the top of the mineral soil surface.
Soil moisture: The soil moisture control section (smcs) is affected by precipitation that falls evenly throughout the year with the exception of a significant increase in July and August. The smcs is driest during the fall. The smcs is too dry for Udic and is considered to have an Ustic soil moisture regime.
Mean annual soil temperature: 40 degrees F.
Particle-size control section: 18 to 27 percent clay, 35 to 55 percent rock fragments
Thickness of mollic epipedon: 10 to 15 inches.
Depth to cambic horizon: 10 to 15 inches
A horizon:
Hue: 7.5YR or 10YR
Value: 3 to 5 dry, 2 or 3 moist
Chroma: 2 or 3 dry, 1 or 2 moist
Reaction: slightly acid (pH 6.1) to neutral (pH 7.3)
Rock fragments: granite, granodiorite, granodiorite gneiss, or quartz monzonite. 10 to 45 percent total rock fragments; 10 to 45 percent gravel, 0 to 15 percent cobbles.
Bt horizon:
Hue: 7.5YR or 10YR
Value: 5 or 6 dry, 3 or 4 moist
Chroma: 3 or 4 dry or moist
Texture: very gravelly sandy clay loam, very gravelly loam (clay content is not sufficient to qualify for an argillic horizon)
Reaction: slightly acid (pH 6.1) to neutral (pH 7.3)
Rock fragments: granite, granodiorite, granodiorite gneiss, or quartz monzonite. 35 to 55 percent total rock fragments; 25 to 45 percent gravel, 5 to 20 percent cobbles.
COMPETING SERIES: These are the Antrobus, Grafen, Greyback, Handran, Maurice, Parachute, Sebud, Supervisor, Surdal, Teemat, Thornburgh, Tiban and Tineman series.
Antrobus: lacks clay films and formed in materials derived from basalt
Grafen: paralithic contact at 20 to 40 inches
Greyback,
Teemat, Tiban: lacks clay films and has accumulations of secondary calcium carbonate
Handran,
Maurice,
Sebud,
Thornburgh, Tineman: lacks clay films
Parachute,
Supervisor, Surdal: lithic contact at 20 to 40 inches
GEOGRAPHIC SETTING:
Parent material: slope alluvium and colluvium from granite, granodiorite, granodiorite gneiss, or quartz monzonite
Landform: mountain slopes
Slopes: 5 to 40 percent
Elevation: 8,900 to 10,600 feet
Mean annual temperature: 34 to 41 degrees F.
Mean annual precipitation: 21 to 25 inches
Frost-free period: 50 to 70 days
GEOGRAPHICALLY ASSOCIATED SOILS: These are the Grayhead and Storm soils. Grayhead soils are on toeslopes and have a mollic epipedon that is more than 16 inches thick. Storm soils are on backslopes and lack a mollic epipedon.
DRAINAGE AND PERMEABILITY: well drained; medium to very high runoff; moderate permeability.
USE AND VEGETATION: This soil is used for wood products. Potential native vegetation is quaking aspen with an understory of bearded wheatgrass, slender wheatgrass, elk sedge, and nodding bromegrass. It is in the Quaking Aspen Woodland Site, Forest Cover Type 217.
DISTRIBUTION AND EXTENT: Western Colorado in LRR E and MLRA 48A. The series is of small extent.
MLRA SOIL SURVEY REGIONAL OFFICE (MO) RESPONSIBLE: Bozeman, Montana
SERIES ESTABLISHED: Cochetopa Soil Survey Area, Gunnison National Forest, Gunnison County, Colorado, 1999. The name comes from Van Wirt Mountain.
REMARKS: Diagnostic horizons and features recognized in this pedon.
Mollic epipedon: the zone from 2 to 16 inches. (A horizon)
Cambic horizon: the zone from 16 to 66 inches. (Bt horizon) Clay increase does not meet requirement for argillic horizon as supported by field hydrometer results.
Taxonomic version: Eighth Edition, 1998.