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<br />Ii10 GRANDE COUNTY AREA, COLORADO
<br />diversions are uniformitc and steepness of slope; depth
<br />to bedrock or other unfavorable material; stones; per-
<br />me56ilily;and resistance to +vater erosion, soi! slipping,
<br />and soil blowing. A soil suitable for these strucrin'es
<br />provides outlets for runoff and is not r1i(licult to vege-
<br />tate.
<br />Pesercoirs hold n•ater behind a dam or emhnnkment.
<br />Soils suitable as pond reservoir at'eus base loin seepage,
<br />which is related to their perme:rbilitc and depth to
<br />fractureil or permeable berh'ock or other permeable
<br />material.
<br />P;mbanlanents require loll material rosi.eLutt to seep-
<br />age anti pipin;{ and of favnrabfe sLt6ilily, shrink-swell
<br />potenti;d, shear strength, and compaclibilih. Stones
<br />anti nrg;utir material in a soil are among Ieatures that
<br />arc unfavorable.
<br />Agriculhu'al drainage is affected b} such soil proper-
<br />ties as permeability, texture, ;utd slruc4tre: depth to
<br />clncpan. rock, or other lacers that influence rate of
<br />water movement; depth to the water table; slope, sta-
<br />bility in rlitchb;mks; susceptibility to sire:mt overflow;
<br />salinih' a' alkalinity : and availability of outlets for
<br />drainage.
<br />Irrigation of a soil is affected by such features as
<br />slope; susceptibility to stream overflow, venter erosion,
<br />or soil blowing; soil texhn'e; content of stones; accu-
<br />mulation oC salts ;lad alkali; depth of root ante; rate of
<br />water inL•tke at the surface: permeability of the soil
<br />below the surface layer ;utrl in a fra~,ipan or other
<br />lacer that restricts movement nF hater; amount of
<br />water held available to plants; nerd for di;tinage; attd
<br />depth to the water table or bedrock.
<br />Sni7 7e.cf rinln
<br />Table S contains engineerinl,* test riata Cor stone of
<br />the major soil series in P.io Grande Counts Area. These
<br />tests tr ere made to help ev;dunte the soils for engineer-
<br />ing purposes. 'Che engineering classifications given are
<br />based on data obtained by mechanical analyses :cod by
<br />tests to determine liquid limit anti plastir• limit. The
<br />mechanical annlvses were merle by combiner) niece and
<br />hych'ometer methods.
<br />Compaction. ur nutisture-density, data are important
<br />in earthwa'k. If a soil material is cnmpacterl at suc-
<br />cessivey' higher moisture content. assuming that the
<br />contpactive effort remains constant, the rlensitc of the
<br />compacted material increases until the op/innut+ mois-
<br />lamc rn17GrPC IS reached. ACter that, density decreases
<br />with increase in moi.eture content. The highest rlr}' den-
<br />sity obtained in the compactice test is termed ~7rnzi-
<br />namn. rhvt r/en.erl7/. Asa rule, m;uinnnn strength of
<br />eartho-orl: is nblainerl if the soil is compacted to the
<br />maximum rlry density.
<br />1•ests to determine liquid limit and plastic limit mea-
<br />sure the effect nC e•ater nn the consistence of soil mate-
<br />rial, as explainer) fa• table G.
<br />F'urmaliun and Classification of thr.tiuils
<br />This section describes some n[ the ch;rr,tcteristics of
<br />the soils of the Pio Grande County Area :ctrl Lells how
<br />they arc related to the factm~s of soil inrmatiun. It also
<br />explains the system of soil classificntirnt and classifies
<br />the soils in the survey area according to that system.
<br />Factors of Soil Portnation ~
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<br />Soil is the collection of natu •al bodies nn fire earth's
<br />surface, iu places modified of even made by man of
<br />earthy materials containing li ing matter and support-
<br />ing m' capable of supporting (ants. Soils differ in ap-
<br />pearance, composition, produc ivity, and management
<br />requirements in different locali ies or even within short
<br />distances in the same locality.
<br />The interaction of flee coal factors cause soils to
<br />differ. These are the physical a d chemical composition
<br />of the parent material; the c inrtte under which the
<br />parent material accumulated ar d existed since accumu-
<br />lation; the kinds of plants and nrganiwns living in the
<br />soil; the relief, m• lay of the Innd, and its effect on
<br />runoff; and the length of tim the soil farming pro-
<br />cesses have acted. General)}',along period is required
<br />for the formation of distinct s it horuons.
<br />The relative importance of tch factor differs from
<br />place to place but the intern lion of all the factors
<br />determines the kind of soil th tt forms in any given
<br />place. In the following pages, tl e f;tctors of soil forma-
<br />tion are defined as related to t eh effects on the soils
<br />of the survey area.
<br />Pnren! mnlerinl
<br />Parent material is the material in which soil forms.
<br />It can be material that has wen hexed in place or that
<br />has been h'ansported by wind o water. In many soils
<br />there is no distinct difference b weer the soil material
<br />in the lower part of the profile and the parent mate-
<br />rial. P;u'ent material affects s it formation in many
<br />ways. It largely determines the exture, structure, con-
<br />sistency, calm, ;cod sometimes m 'angement of the hori-
<br />zmts. It affects the rate of soil rmntion according to
<br />its resistance to n'cathering. F r example, suulc ~utd
<br />gravely' parent material weatf ern slowly, therefore
<br />soils formed in such material al generally sandy anti
<br />have weak hm•izon differential on. Afedium textured
<br />parent material generaly~ went) ers more readil}' and
<br />the soils famed are more lihey to he loamy and have
<br />stronger horizon rli(fcrentiation. Parent material also
<br />affects the inherent fertility and the erodibility of the
<br />soil. The soils of the Rio Grande County Area fm•med
<br />in three major kinds of paten material: alluvium,
<br />slope-wash, and volcanic rocks o Tertiary age.
<br />Soils formed in ;tlluvium are he most extensive in
<br />the sur~~e} area. There is a wi c range in the com-
<br />position of the alluvium. depe7 ding largely on the
<br />rocks from n•hich it weathered, he distance from its
<br />source, and the topngraph>•. Ac:ts o, Alamosa, Gerrard,
<br />Schrader, Shawn, and Vnstine s its formed in mnder-
<br />ately fine textured to moderately coarse testnred allu-
<br />vium deposited by the Rio Gran e, Fock Creek, Pinos
<br />Creek, and other major creeks. S me of these soils are
<br />wtderlain within a depth of 40 aches by coarse tex-
<br />tured material The potent mater al depnsiteri by these
<br />streams was derived from areas i aving large amounts
<br />of volcanic rocks, mainy quartz atite, anrlesite, rhyo-
<br />lite, and basalt f11, /3). Aiost f this material was
<br />transported a long distance.
<br />Acacia, Laney, Luhon, Diishak, Ionte. Stunner, Villa
<br />Grote, and Zinzer soils formed 'n medium tcxhu'erl
<br />calcareous alluvium. This parent material m~iginated
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