LOCATION LARKSON                 CO+SD WY

Established Series
Rev. GB/KLS
07/2022

LARKSON SERIES

The Larkson series consists of deep, well and moderately well drained, slowly permeable soils that formed in materials weathered in place or only locally transported from soft noncalcareous sedimentary deposits. Larkson soils are on fans, footslopes, valley sideslopes, hills, and ridges with slopes of 2 to 60 percent. The mean annual precipitation is about 430 mm and the mean annual temperature is about 6 degrees C.

TAXONOMIC CLASS: Fine, smectitic, frigid Typic Haplustalfs

TYPICAL PEDON: Larkson loamy coarse sand, forest. (Colors are for dry soil unless otherwise noted).

Oi--0 to 3 cm; undecomposed organic material consisting mainly of needles, bark, twigs, and leaves.

Oe--3 to 6 cm; partially decomposed organic material like that of the horizon above.

A--6 to 11 cm; very dark gray (10YR 3/1) loamy coarse sand, black (10YR 2/1) moist; strong fine crumb structure; soft, very friable; slightly acid, clear smooth boundary. (0 to 13 cm thick)

E--11 to 57 cm; light brownish gray (10YR 6/2) loamy coarse sand, dark grayish brown (10YR 4/2) moist; moderate thin platy structure parting to fine granular; soft, very friable; vesicular; neutral; gradual wavy boundary. (13 to 50 cm thick)

E/B--57 to 72 cm; light brown (7.5YR 6/3) coarse sandy clay loam, (composite texture) brown (7.5YR 5/4) moist; moderate medium subangular blocky structure; slightly hard, very friable, slightly sticky and slightly plastic; peds are very hard, friable; 10 percent fine angular granite pebbles; nodules and seams of clayey material like that of the underlying horizon embedded in a matrix like that of the overlying horizon; slightly acid; gradual wavy boundary. (10 to 25 cm thick)

Bt--72 to 102 cm; variable colors including very pale brown (10YR 7/3) and light reddish brown (2.5YR 6/4) clay, light yellowish brown (10YR 6/4) and reddish brown (2.5YR 5/4) moist; moderate medium subangular blocky structure; friable, sticky and plastic; peds are extremely hard, firm; continuous clay films on peds and in root channels and pores; 10 percent fine angular granite pebbles; neutral; gradual wavy boundary. (15 to 70 cm thick)

BC--102 to 117 cm; variable colors including very pale brown (10YR 7/3) and light reddish brown (2.5YR 6/4) clay, light yellowish brown (10YR 6/4) and reddish brown (2.5YR 5/4) moist; moderate medium subangular blocky structure; hard, friable, sticky and plastic; peds are extremely hard, firm; clay films on some faces of peds, and in some root channels and pores; 5 to 10 percent fine angular granite pebbles and few shale fragments; slightly alkaline; gradual smooth boundary. (10 to 20 cm thick)

C--117 to 158 cm; variable colors including very pale brown (10YR 7/3) and light reddish brown (2.5YR 6/4) gritty heavy clay loam, pale brown (10YR 6/3) and reddish brown (2.5YR 5/4) moist; massive; extremely hard, firm, sticky and plastic; slightly alkaline.

TYPE LOCATION: Douglas County, Colorado; 53 meters east and 27 meters south of the cattle guard at the entrance to the Sinclair summer home in sec. 7, T. 9 S., R. 67 W.

RANGE IN CHARACTERISTICS:
Mean annual soil temperature--7 degrees C
Mean summer soil temperature--18 degrees C
Base saturation--60 to 100 percent in all subhorizons of the argillic horizon
Rock fragment content--0 to 35 percent; mainly less than 75 mm in diameter and ranging from 3 mm to more than 250 mm in diameter
A thin A horizon is generally present but may be absent in some pedons.
The soils are calcareous below 100 cm in some pedons.

Sediments of the parent Dawson and Arapaho formations occur above 100 cm in some pedons but are of such low contrast that they cannot be consistently recognized from the C horizon.

The A and E horizons typically are uniform in color but the rest of the solum ranges in hue from 2.5Y through 2.5YR as a natural feature of the parent materials. Ranges in color listed below are those normally found for crushed color of the composite horizon. Actual variation is often greater than indicated.

A horizon
Hue--2.5Y through 7.5YR when crushed
Value--4 through 6 dry, 2 through 4 moist
Chroma--1 through 4
Reaction--pH 6.4 to 7.4

E horizon
Hue--2.5Y through 7.5YR when crushed
Value--5 through 8 dry, 4 through 7 moist
Chroma--1 through 4
Reaction--pH 6.2 to 7.2

Bt horizon
Hue--2.5Y through 7.5YR
Value--5 through 7 dry, 4 through 6 moist
Chroma--1 through 6
Texture--heavy clay loam or clay
Reaction--pH 6.4 to 7.6

C horizon
Hue--2.5Y through 7.5YR and is commonly variable but some pedons have uniform colors
Texture-- heavy clay loam, loam or light clay
Reaction--pH 6.4 to 7.6

COMPETING SERIES: These are the Campspass, Citadel, Fortwingate, Goldvale, Osoridge, Pylon, Rolla, Virkula and Zuni series. Fortwingate, Osoridge, and Pylon soils have bedrock at a depth of less than 100 cm. Campspass, Citadel, and Rolla soils are calcareous in the lower part of the solum and in the C horizon, have subhorizons of secondary calcium carbonate accumulation, and lack the variability of soil color found in the Larkson soils. Goldvale soils have uniform color of 5YR or redder in the major part, have a solum thicker than 140 cm to the base of the argillic horizon, and more than 60 cm to the top of the argillic horizon, and have a sandy loam C horizon. Zuni soils have uniform hue of 5YR or redder in a major part of the solum. Virkula soils formed in a silty mantle over residuum from igneous and metamorphic rocks and are more acid.

GEOGRAPHIC SETTING:

Landform--fans, footslopes, valley sideslopes, hills and ridges
Elevation--2125 to 2450 meters
Slope--2 to 60 percent
Parent Material--slope alluvium, colluvium and/or residuum
Mean annual precipitation--400 to 480 mm with peak periods of precipitation in the spring and early summer
Mean annual air temperature--6 to 7 degrees C

GEOGRAPHICALLY ASSOCIATED SOILS: None listed

DRAINAGE AND PERMEABILITY: Well drained or moderately well drained; slow permeability.

USE AND VEGETATION: These soils are used primarily for forestry, grazing, or for recreation. Native vegetation is mainly relatively heavy stands of ponderosa with an understory of shrubs and grasses.

DISTRIBUTION AND EXTENT: Larkson soils are moderately extensive in the foothills along the eastern Rocky Mountain front in Colorado and Wyoming and in the Black Hills area of South Dakota; MLRAs 49, 61

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

SERIES ESTABLISHED: Pueblo Area, Colorado, 1974

REMARKS: Converted to metric, updated formatting, and O horizons were updated to start at zero. 5/2022

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National Cooperative Soil Survey
U.S.A.