LOCATION BROSS                   CO+WY

Established Series
Rev. DKA/GB/KLS
07/2022

BROSS SERIES

The Bross series consists of deep, well to moderately well drained soils that formed in slope wash or alluvial fan sediments from mixed crystalline rocks. Bross soils are on alpine hills and ridges above timberline. Slopes range from 2 to 50 percent. The mean annual precipitation is about 890 mm and the mean annual temperature is about -2 degrees C.

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--0 to 3 cm; undecomposed grass remains.

Oe--3 to 6 cm; partially decomposed organic materials, mainly grasses.

A1--6 to 26 cm; 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. (18 to 38 cm thick)

A2--26 to 36 cm; 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 15 cm thick)

Bw--36 to 67 cm; 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. (15 to 46 cm thick)

C--67 to 158 cm; 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--about -1 degree C
Mean summer soil temperature--6 degrees C
Reaction--pH 5.1 to 5.5 to depths of more than 100 cm, but becoming somewhat less acid with increasing depth in some pedons
Base saturation--30 to 50 percent in the umbric epipedon and at least some of the Bw horizon is less than 60 percent base saturated
Thickness of umbric epipedon--18 to 38 cm
Particle-size control section--sandy loam with gravelly or very gravelly modifier
Clay content--5 to 18 percent
Silt content--5 to 35 percent
Sand content--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.
Total rock fragments--35 to 80 percent by volume in a major part of the particle size control section and typically range in diameter from 6 to 250 mm; lower parts of the particle size control section may have up to 20 percent stones
Moisture control section--moist from snow melt when the soil is not frozen

A horizon
Hue--2.5Y through 7.5YR
Value--3 through 5 dry, 2 or 3 moist
Chroma--1 through 4

Bw horizon
Hue--2.5Y through 7.5YR
Value--5 through 7 dry, 3 through 6 moist
Chroma--1 through 6
Reaction--pH 4.5 to 6.0

C horizon
Hue--2.5Y through 7.5YR
Reaction--pH 4.5 to 6.5
Mottling (7.5YR 4/6) is common at depths of 75 cm.

COMPETING SERIES: These are the Mirror and Penitente series. Mirror soils have a lithic contact at depths of less than 100 cm. Penitente soils have Bir horizons.

GEOGRAPHIC SETTING:
Landform--alpine hills and ridges above timberline
Elevation--3,050 to 4,275 meters
Slopes--2 to 50 percent
Parent material--sediments locally transported as slope wash or alluvial fan sediments from a mixture of crystalline rock
Mean annual precipitation--510 to 1,300 mm, most of which comes as snow
Mean annual air temperature--about -2 degrees C
Frost-free period--less than 10 days

GEOGRAPHICALLY ASSOCIATED SOILS: None listed

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: Bross soils of moderate extent in the mountainous areas of central and southwestern Colorado and north-central Wyoming; MLRAs 43B, 48A

SOIL SURVEY REGIONAL OFFICE (SSRO) RESPONSIBLE: Bozeman, Montana

SERIES ESTABLISHED: Lake County, Colorado; 1974

REMARKS: The differentiae between the Bross and Penitente series need further study.

Converted to metric and O horizons were updated to start at zero. 3/2022

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National Cooperative Soil Survey
U.S.A.