LOCATION BROSS CO+WYEstablished Series
TAXONOMIC CLASS: Loamy-skeletal, isotic Typic Humicryepts
TYPICAL PEDON: Bross very gravelly sandy loam - alpine grassland. (Colors are for dry soil unless otherwise noted.)
Oi--2 inches to 1 inch; undecomposed grass remains.
OE--1 inch to 0; partially decomposed organic materials, mainly grasses.
A1--0 to 8 inches; grayish brown (10YR 5/2) very gravelly sandy loam, very dark grayish brown (10YR 3/2) moist; strong fine granular structure; soft, very friable; 60 percent pebbles and some cobbles; strongly acid; clear smooth boundary. (7 to 15 inches thick)
A2--8 to 12 inches; pale brown (10YR 6/3) very gravelly sandy loam, brown (10YR 5/3) moist; weak fine platy structure parting to fine granules; soft, very friable, vesicular; 60 percent pebbles and some cobbles; strongly acid; clear wavy boundary. (0 to 6 inches thick)
Bw--12 to 24 inches; light yellowish brown (10YR 6/4) very gravelly sandy loam, yellowish brown (10YR 5/4) moist; moderate fine subangular blocky structure; slightly hard, very friable; dark pellets and concretions; 55 percent pebbles and some cobbles; strongly acid; gradual wavy boundary. (6 to 18 inches thick)
C--24 to 60 inches; pale brown (10YR 6/3) extremely gravelly sandy loam, brown (10YR 5/3) moist; massive; slightly hard, very friable; 70 percent pebbles and some cobbles; strongly acid.
TYPE LOCATION: Lake County, Colorado; along the road to Mosquito Pass; aerial photograph DZ2-16-31; T. 9 W., R. 79 W.
RANGE IN CHARACTERISTICS: Mean annual soil temperature is about 30 degrees F., and mean summer soil temperature is about 42 degrees F. The soils typically are strongly acid to depths of more than 40 inches but in some pedons become somewhat less acid with increasing depth. Base saturation ranges from 30 to 50 percent in the umbric epipedon and at least some subhorizon of the Bw horizon is less than 60 percent base saturated. The umbric epipedon ranges from 7 to 15 inches thick. The particle size control section is usually gravelly or very gravelly sandy loam. The fine earth fraction has 5 to 18 percent clay, 5 to 35 percent silt, and 50 to 80 percent sand with more than 35 percent being fine or coarser sand. Loamy sand or coarser textures are excluded from the above range. Rock fragments range from 35 to 80 percent by volume in a major part of the particle size control section and typically range in diameter from 1/4 to 10 inches. The moisture control section is usually moist from
snow melt when the soil is not frozen. The lower parts of the particle size control section may have up to 20 percent stones.
The A horizon has hue of 2.5Y through 7.5YR, value of 3 through 5 dry, and 2 or 3 moist, with chroma of 1 through 4.
The Bw horizon has hue of 2.5Y through 7.5YR, value of 5 through 7 dry, and 3 through 6 moist, with chroma of 1 through 6. It ranges from medium acid to very strongly acid.
The C horizon has hue of 2.5Y through 7.5YR. It ranges from slightly acid to very strongly acid. Mottling of 7.5YR 4/6 is common at depths of 30 inches.
COMPETING SERIES: These are the Mirror and Penitente series. Mirror soils have a lithic contact at depths of less than 40 inches. Penitente soils have Bir horizons.
GEOGRAPHIC SETTING: Bross soils are on alpine hills and ridges above timberline. Slopes range from 2 to 50 percent. The soil formed in parent sediments locally transported as slope wash or alluvial fan sediments from a mixture of crystalline rock. Elevation ranges from 10,000 to 14,000 feet. Average annual precipitation is 35 inches, most of which comes as snow. The mean annual precipitation ranges from 20 to 50 inches. Mean annual air temperature is 28 degrees F. Frost-free season is less than 10 days.
GEOGRAPHICALLY ASSOCIATED SOILS: These are the competing Mirror soils and the Ptarmigan soils. Ptarmigan soils have coarse-loamy particle size control sections.
DRAINAGE AND PERMEABILITY: Well drained; medium to rapid runoff; moderately rapid permeability.
USE AND VEGETATION: These soils are used principally for native pastureland, although they have some value for recreational purposes. Native vegetation consists of kobresia, sedges, alpine bluegrass, tufted hairgrass, dry willows, and alpine clover.
DISTRIBUTION AND EXTENT: Mountainous areas of central and southwestern Colorado and adjacent parts of New Mexico. The series is of moderate extent.
MLRA OFFICE RESPONSIBLE: Lakewood, Colorado
SERIES Established: Lake County, Colorado; 1974.
REMARKS: The differentiae between the Bross and Penitente series need further study.