LOCATION ZILLMAN WY+COEstablished Series
TAXONOMIC CLASS: Loamy-skeletal, mixed, superactive, frigid Aridic Argiustolls
TYPICAL PEDON: Zillman very gravelly loam-rangeland. (Colors are for dry soil unless otherwise stated.)
A--0 to 5 inches; grayish brown (10YR 5/2) very gravelly loam, very dark grayish brown (10YR 3/2) moist; strong fine granular structure, slightly hard, very friable, slightly sticky and slightly plastic; common fine and very fine roots; 30 percent pebbles and 10 percent cobbles; mildly alkaline (pH 7.7); clear smooth boundary. (4 to 6 inches thick)
BA--5 to 8 inches; brown (10YR 5/3) very gravelly loam, dark brown (10YR 3/3) moist; moderate fine subangular blocky structure parting to strong fine granular; hard, friable, slightly sticky and slightly plastic; common fine roots; few thin clay films on faces of peds; 30 percent pebbles and 10 percent cobbles; mildly alkaline (pH 7.8); clear smooth boundary. (3 to 5 inches thick)
Bt--8 to 15 inches; brown (10YR 5/3) very gravelly clay loam, dark brown (10YR 4/3) moist; strong fine subangular blocky structure; very hard, firm, sticky and plastic; few fine roots along ped faces; common moderately thick clay films on faces of peds, few thin to moderately thick clay films on coarse fragments; 40 percent pebbles and 10 percent cobbles; mildly alkaline (pH 7.5); clear wavy boundary. (6 to 20 inches thick)
Btk--15 to 18 inches; pale brown (10YR 6/3) very gravelly clay loam, brown (10YR 5/3) moist; strong medium subangular blocky structure; hard, friable, sticky and plastic; few fine roots; few thin clay films on faces of peds; strongly effervescent, lime as common soft masses and in seams; 40 percent pebbles and 20 percent cobbles; moderately alkaline (pH 8.3); gradual wavy boundary. (0 to 5 inches thick)
Bk--18 to 60 inches; light yellowish brown (2.5Y 6/4) gravelly loam, light olive brown (2.5Y 5/4) moist; massive; hard, friable, slightly sticky and slightly plastic; strongly effervescent, lime as common soft masses and few coatings on coarse fragments; 40 percent pebbles and 20 percent cobbles; moderately alkaline (pH 8.3).
TYPE LOCATION: Lincoln County, Wyoming. Approximately 1,848 feet west and 330 feet south of the east quarter corner of sec. 2, T. 21 N., R. 116 W.
RANGE IN CHARACTERISTICS: The mollic epipedon is 7 to 15 inches thick. Depth to the base of the argillic horizon ranges from 15 to 30 inches. The mean annual soil temperature ranges from 42 to 46 degrees F., and the mean summer temperature ranges from 59 to 63 degrees F.
The A horizon has hue of 5Y through 7.5YR, value of 4 or 5 dry, 2 or 3 moist, and chroma of 2 or 3. Reaction is neutral or mildly alkaline.
The Bt horizon has hue of 5Y through 7.5YR, value of 4 through 6 dry, 3 through 5 moist, and chroma of 2 through 4. Matrix texture is clay loam or loam with 18 to 35 percent clay and less than 35 percent fine or coarser sand. Coarse fragments range from 35 to 80 percent and are made up of pebbles, cobbles, and stones which can occur in any combination. Flagstones occur in some pedons. It is neutral or mildly alkaline.
The Bk horizon has hue of 5Y through 7.5YR, value of 5 through 7 dry, 4 through 6 moist, and chroma of 2 through 4. Texture is the same as the Bt except that clay ranges from 18 to 30 percent. Calcium carbonate equivalent ranges from 6 to 14 percent. It is moderately alkaline or strongly alkaline.
COMPETING SERIES: These are the Badito, Beaverell, Circleville, Ipson, San Isabel, Simmont, and Uracca series. The Badito series has tuff above 40 inches and lacks free carbonates throughout. The Beaverell, San Isabel, and Uracca soils have very gravelly sand C or Bk horizons at a depth of 10 to 20 inches. Circleville and Simmont soils have hard bedrock at 20 to 40 inches. Ipson soils have a calcic horizon.
GEOGRAPHIC SETTING: The Zillman soils are on terraces, upper fan aprons, and mountain slopes. They formed in slope alluvium and sediments derived from mixed sources. Slopes are 2 to 65 percent. Elevations are 6,500 to 7,800 feet. The mean annual precipitation is about 13 inches and ranges from 10 to 16 inches of which about half falls as rain or snow in April, May, and early June. The mean annual temperature is about 41 degrees F. and ranges from 38 to 43 degrees F. The frost-free season is 50 to 90 days.
GEOGRAPHICALLY ASSOCIATED SOILS: These are the Curecanti and the competing Ipson and Simmont soils. Curecanti soils have darker surface layers when dry and receive more effective moisture due to additional snowpack.
DRAINAGE AND PERMEABILITY: Well drained; medium to moderately rapid runoff depending upon slope; moderate permeability.
USE AND VEGETATION: Rangeland and wildlife habitat. Native vegetation consists of bluebunch wheatgrass, needleandthread, black sagebrush, thickspike wheatgrass, and some big sagebrush.
DISTRIBUTION AND EXTENT: Mountains and basins of Wyoming and northwestern Colorado. The series is of moderate extent.
MLRA SOIL SURVEY REGIONAL OFFICE (MO) RESPONSIBLE: Bozeman, Montana
SERIES ESTABLISHED: Aspen-Gypsum Area, Colorado; 1982.