LOCATION HILLTOPPE WYEstablished Series
TAXONOMIC CLASS: Loamy-skeletal, carbonatic, shallow Calcic Petrocalcids
TYPICAL PEDON: Hilltoppe very gravelly sandy loam, on a planar northeast facing slope of two percent, in rangeland. (Colors are for dry soil unless otherwise stated.) The surface has 30 percent pebbles.
A--0 to 3 inches; brown (10YR 5/3) very gravelly sandy loam, dark grayish brown (10YR 4/2) moist; weak fine granular structure; soft, very friable, nonsticky and nonplastic; many fine roots and pores; strongly effervescent, disseminated carbonates and pendant fragments (calcium carbonate equivalent of 15 percent); about 40 percent medium and fine quartzite pebbles; moderately alkaline (pH 8.2); clear smooth boundary. (3 to 5 inches thick)
Bk1--3 to 8 inches; pale brown (10YR 6/3) very gravelly sandy loam, brown (10YR 5/3) moist; very weak fine subangular blocky structure; soft, very friable, nonsticky and nonplastic; common fine roots and pores; violently effervescent, disseminated carbonates and many pendants and pendant fragments (calcium carbonate equivalent of 42 percent); about 50 percent medium quartzite pebbles; moderately alkaline (pH 8.2); clear smooth boundary. (4 to 10 inches thick)
Bk2--8 to 14 inches; very pale brown (10YR 7/3) extremely gravelly sandy loam, pale brown (10YR 6/3) moist; massive; soft, very friable, nonsticky and slightly plastic; few fine roots and pores; violently effervescent, disseminated carbonates and many pendants and pendant fragments (calcium carbonate equivalent of 51 percent); about 75 percent medium and coarse quartzite pebbles and few cobbles; moderately alkaline (pH 8.2); abrupt smooth boundary. (0 to 6 inches thick)
Bkm--14 to 33 inches; petrocalcic horizon consisting of about 40 percent quartzite pebbles and 30 percent quartzite cobbles in an indurated, laminated calcium carbonate matrix. (4 to 19 inches thick)
Ck--33 to 60 inches; pale brown (10YR 6/3) extremely gravelly sandy loam, brown (10YR 5/3) moist; massive; soft, very friable, nonsticky and nonplastic; strongly effervescent, disseminated carbonates (calcium carbonate equivalent of 25 percent); about 50 percent quartzite pebbles and 20 percent fine quartzite cobbles; moderately alkaline (pH 8.2).
TYPE LOCATION: Albany County, Wyoming; 2,080 feet north and 25 feet east of the southwest corner of Section 33, T16N, R76W.
RANGE IN CHARACTERISTICS: Depth to the petrocalcic horizon ranges from 10 to 20 inches. Coarse fragments in the control section range from 25 to 60 percent pebbles and 0 to 40 percent cobbles. Clay content in the control section ranges from 8 to 18 percent. The mean annual soil temperature is 40 to 45 degrees F.
The A horizon has hue of 7.5YR through 2.5Y, value of 5 or 6 dry, 3 or 4 moist, and chroma of 2 or 3 dry and moist. Surface horizons under long-term irrigation may have mollic colors provided they are less than 3 inches thick. Texture is sandy loam or fine sandy loam with gravelly, very gravelly, cobbly, or very cobbly modifiers. Reaction is mildly alkaline or moderately alkaline.
The Bk horizons have hue of 7.5YR through 2.5Y, value of 6 through 8 dry, 6 or 7 moist, and chroma of 1 through 3 dry and moist. Texture is sandy loam or fine sandy loam with very gravelly, extremely gravelly, very cobbly, or extremely cobbly modifiers. Calcium carbonate equivalent ranges from 40 to 60 percent. Reaction is moderately alkaline or strongly alkaline.
The Bkm horizon consists of 45 to 75 percent by volume pebbles and cobbles in an indurated, laminated calcium carbonate matrix. Very thin, discontinuous laminations of a harder substance, possibly silica, have been observed in some pedons. This diagnostic petrocalcic horizon can be broken along original pendant bridgings with a geology pick and excavated with difficulty by a backhoe.
The Ck horizon has hue of 7.5YR through 2.5Y, value of 6 or 7 dry, 5 or 6 moist, and chroma of 2 or 3 dry and moist. Texture is sandy loam, fine sandy loam, or loam with very gravelly or extremely gravelly modifiers. Calcium carbonate equivalent ranges from 10 to 30 percent. Reaction is moderately alkaline or strongly alkaline.
COMPETING SERIES: There are no competing series. Ashuelot series are similar. Ashuelot soils have a mollic epipedon and are classified as loamy, carbonatic, shallow Petrocalcic Calciborolls.
GEOGRAPHIC SETTING: Hilltoppe soils are on nearly level to gently sloping relict fan terraces. Slopes are 0 to 8 percent. Elevation is 7,000 to 7,800 feet. The mean annual precipitation is about 12 inches of which about half falls as snow or rain in April, May, and early June. The mean annual temperature is about 43 degrees F. The frost-free season is 85 to 100 days.
GEOGRAPHICALLY ASSOCIATED SOILS: These are the Browtine (T) and McFadden soils. Browtine soils do not have petrocalcic horizons. McFadden soils have coarse-loamy control sections.
DRAINAGE AND PERMEABILITY: Well drained; runoff is slow; moderately rapid permeability.
USE AND VEGETATION: These soils are used as rangeland and for irrigated hayland and pasture. The native vegetation is Hood phlox, bluebunch wheatgrass, prairie junegrass, and broom snakeweed.
DISTRIBUTION AND EXTENT: Basins of southeast Wyoming. The series is not extensive.
MLRA SOIL SURVEY REGIONAL OFFICE (MO) RESPONSIBLE: Bozeman, Montana
SERIES ESTABLISHED: Albany County (Albany County Area), Wyoming; 1991.
REMARKS: Diagnostic horizons and features recognized in this pedon are: Ochric epipedon - 0 to 3 inches (A); Calcic horizon - 3 to 14 inches (Bk1, Bk2); Petrocalcic horizon - 14+ inches (Bkm); Borollic feature--Frigid temperature regime and 0.5 percent organic carbon - 0 to 3 inches (A).