WSP00945

• File Number: 8442.400
• Description: Missouri Basin - Pick Sloan Project - Reports
• State: CO
• Basin: South Platte
• Water Division: 1
• Date: 2/28/1985
• Author: DoI, BoR
• Title: Lake Andes - Wagner Unit Planning Report / draft Enviromental Statement
• Water Supply Pro - Doc Type: Report/Study

glacial drift was covered by 1 to 2 feet of loess and that the soils owe
their origin to both glacial till and loess. The glacial till is heavily
influenced by the siltstone residuum from the Niobrara formation which
underlies the glacial drift to the north. ; The material above the till has
been so modified by weathering that po~itive identification as loess is not
possible.

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The soils of the project area are deep, medium-textured mollisols.

Although these soils vary to some degr~e in their suitability for sustained

irrigation fa~ing, they have certain ~omm~n characteristics; namely, they

are deep and have very dark-gray to datk-brown friable surface soils. The

surface soils are usually noncalcareous, easily tilled, and readily recep-

tive to air, water, and root penetration. The zone of lime accumulation

starts at depths from 14 to 30 inches, depending upon texture and degree of

slope. Surface soils are relatively stone-free. Waterho1ding capacity is

good. Friable till that is moderately de~se characterizes all arable soil

profiles beginning at the bottom of the l~me zone, which in these soils

occurs at 24 to 40 inches beneath the surface.

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Silt loam is the dominant texture of Surface soils, while subsoils below 14

to 24 inches are clay loams. Light clay ~ubsoils occur in some areas.

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Topography is smooth but irregular, with ~ gentle overall gradient toward

Choteau Creek or Lake Andes. The sufface;is mildly undulating with occa-

sional small closed depressions, shallow ~rainways, and a complexity of

slopes, sometimes long and gentle or short and steep, and often mildly in

reverse of the gentle general slope. Thi$ topography is generally favorable
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for sprinkler irrigation development, andiapproximately 99 percent of the
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arable lands surveyed have no topographic] deficiencies for sprinkler irri-

gat ion.

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Subsoils in the project area are sometimes saline in which part of the

soluble salts are gypsum. Under usual derinitions, some of the subsoils

are also sodic. Oetailed and careful stutlies were made in the field and in

the laboratory which show that, under irr~~ation with adequate drainage,

the salts and sodium will move out of these ,subsoils into the drainage

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