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<br />86 SOIL SURVEY
<br />horizons used to make separations are those in which
<br />clay, iron, or humus has accumulated; those that have
<br />pans that interfere with growth of roots, movement of
<br />water, ot• both; aitd thick, dark-colored surface hori-
<br />zons. The features used are the self-mulching pt•oper-
<br />ties of clay, soil temperature, major differences in
<br />chemical composition (mainly calcium, magnesium, so-
<br />dium, and potassium), dark-red and dark-brown colors
<br />associated with basic rocks, and the like. The names of
<br />great groups have three or four syllables and are
<br />made by adding a prefix to the name of the suborder.
<br />An example is A'atrargid (A'atr, meaning presence of
<br />significant amounts of exchangeable sodium or of so-
<br />dium and magnesium, and argid, the suborder of Aridi-
<br />sols that have an illuvial clay horizon).
<br />SueceouP. Great groups are divided into sub-
<br />groups, one that represents the central (typic) segment
<br />of the group and others, called intergt•ades, that have
<br />properties of the group and also one or more properties
<br />of another great group, suborder, or order. Subgroups
<br />may also be made in those instances where soil prop-
<br />erties intet•grade outside the range of any other great
<br />group, suborder, or order. The names of subgroups are
<br />derived by placing one or more adjectives in front of
<br />the name of the great group. An example is Ustollic
<br />A'atraryids (Ustollic, meaning intergrading to tho sub-
<br />order of Ustolls in the order of Dlollisols).
<br />FAltf ILY. Soil families are established within a sub-
<br />group mainly on the basis of properties important to
<br />the growth of plants ot• on the behavior of soils when
<br />used for engineering. Among the properties considered
<br />are texture, mineralogy, reaction, soil temperature, per-
<br />meability, thickness of horizons, and consistence. A
<br />family name consists of a series of adjectives preceding
<br />the subgroup name. The adjectives are the class names
<br />for textut•e, mineralogy, and so on, that are used as
<br />family differentiae (see table 8). An example is the
<br />fine, montmorillonitic, mesic family of Ustollic Natrar-
<br />gids.
<br />General Nature of the Area
<br />The Pueblo Area is included in parts of two natural
<br />physiographic areas (12). About 95 percent is gently
<br />rolling plains of the upper Arkansas River• Valley.
<br />Elevation of this physiogt•aphic at•ea ranges from
<br />4,400 to 5,800 feet, increasing gradually from east to
<br />west. These undulating to rolling shale plains are
<br />mantled with loess or windblown sand, alluvium, or
<br />outteash in many places. Wide bands of steep slopes
<br />border the Arkansas Ricer and larger tributaries.
<br />Local relief is mostly less than 50 feet but is as much
<br />as 200 feet in places.
<br />About 5 percent of the survey area is foothills of the
<br />southern Rocky 114ouutains. Elevatimt ranges from
<br />5,800 to 8,000 feet. The physiography consists of rug-
<br />ged hilts and low mountains in a nan•ow band along
<br />the eastern slopes of the Rocky -Iountains. The hills
<br />are much dissected, being crossed in many places by
<br />small drainageteays that flow eastward. Local relief
<br />is set-et•al hundred feet in many places.
<br />GI•eenhorn Peak, at an elevation of 10,334 feet, is in
<br />the extreme southwestern part of Pueblo County and
<br />within the San Isabel National Forest. About 32,415
<br />acres of this national fot•est is in Pueblo County but
<br />tt•as not included in the at•ea of this soil survey.
<br />Drainage is provided by the Arkansas River and its
<br />tributaries. The Arkansas Ricer begins near the Conti-
<br />nental Divide in the mountains to the west and flows
<br />eastward near the center of the survey area. Other
<br />perennial streams in Pueblo County that empty into
<br />the Arkansas River are Fountain Creek, the St. Charles
<br />Ricer, Greenhot•n Creek, and the Huerfano River. The
<br />Apishapa River Hows across the southeast corner of
<br />Pueblo County. Except for the Arkansas River, these
<br />drainage~vays become a mere trickle during periods of
<br />drought. Numerous intermittent streams, in a generally
<br />north-south orientation, empty into the Arkansas
<br />River.
<br />Vit•tually all of the mining operations in the Pueblo
<br />Area are concerned with the extraction of sand, gravel,
<br />and clay, Numerous gravel pits along the Arkansas
<br />River and in the western part of Pueblo County pro-
<br />vide gravel for road surfacing and ready-mix concrete
<br />plants. There are seven clay mines from which raw
<br />material is obtained for sewer pipe and brick. There
<br />is one mine of a pat•ticularly pure form of sand from
<br />deep in the Dakota Formation that is used in steel
<br />processing at Pueblo. There is about 18,600 acres of
<br />commercial timber in the western part of the survey
<br />area.
<br />The Pueblo'Area is underlain by beds of limestone,
<br />shale, and sandstone. The limestone and shale contain
<br />no water. Superficial deposits above the limestone yield
<br />small quantities of water in places, which are sufficient
<br />to water livestock. In the northeastern part of Pueblo
<br />County, good-quality stock water •can usually be ob-
<br />tained within a depth of 130 feet. The best source of
<br />water is the Dakota Formation, but water is not ob-
<br />tained in this fot•mation every place wells are dug. It
<br />does yield water in most places in sufficient quantity
<br />and quality for domestic and livestock uses.
<br />The extreme western part of the survey area con-
<br />sists of rough, timber-covered, mountainous terrain.
<br />The timber is of tu•o types, ponderosa pine and mixed
<br />conifer, which consists mostly of Douglas-fir aitd white
<br />fir. Most of the Pueblo Area has short plains grasses,
<br />mainly blue gt•amma and galleta. Some mid and tall
<br />grasses gt•ow in the sandhills in the northeast, along
<br />with scud sagebrush. Eetween the mountains and the
<br />plains is a transition zone of pinyon pine and juniper,
<br />oakbt•ush, mountainmahogany, and numerous species
<br />of grass.
<br />The Pueblo At•ea is at the junction of Federal Ittter•-
<br />state 25, U.S. 50, and State Highway 96. The survey
<br />area also is set•t•ed by four major railroads, one re-
<br />gional airline, and two tt•anscontinental bus companies.
<br />Climate'
<br />The climate in the Pueblo Area is semi-arid. The
<br />average annual precipitation is 11.9 incites. At least
<br />75 percent of the possible sunshine is received in
<br />all months. There is little or no tornado activity of
<br />consequence. The discussion of the climate in the fol-
<br />]owirg paragraphs is based on data from the weather
<br />' Prepared by the National Climatic Center in Asheville, N.C•
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