Soil Survey of Concho County, Texas Page: 65
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65
Formation of the Soils
In this section the factors of soil formation are
described and related to the soils in the survey area. The
characteristics of the soil at any given point are
determined by the physical and mineral composition of
the parent material; the climate under which the parent
material accumulated and has existed since
accumulation; the plant and animal life on and in the soil;
the relief, or lay of the land; and the length of time the
forces of soil formation have acted on the soil material.
All of these factors influence the present characteristics
of every soil, but the significance of each factor varies
from one place to another. In one area one factor can
dominate the formation of a soil, and in another, a
different factor can be more important.
The interrelationship among these five factors is
complex, and the effects of any one factor cannot be
isolated and completely evaluated. Each factor and the
probable effects of each factor are described separately.
Parent Material
Parent material is the unconsolidated mass from which
the soils form. The kind of parent material determines
the limits of the chemical and mineralogical composition
of the soil. In Concho County, the soils formed in
material from three different geological systems-the
Permian, Cretaceous, and Quaternary (3).
Material of the Permian system is mainly interbedded
limy shale, marl, and limestone of the Wichita and Clear
Fork Groups (fig. 16). Several rock formations of
Permian age are in the northern half of Concho County.
The oldest formation is on the eastern side of the
county, and the youngest is on the western side (6).
These formations lie in a north-south direction, and
several of them form prominent east-facing escarpments.
The Lueders, Talpa, and Speck soils formed in material
weathered from limestone and marl. The Throck soils
formed in material weathered from limy shale.
An outstanding topographic feature of the county is
the Brady Mountains, which are part of the Cretaceous
system. The mountains extend from east to west across
the central part of the county and are outlined in most
areas by steep escarpments that are generally north
facing. These hills are capped with limestone of the Fort
Terrett Formation and form the northern edge of the
Edwards Plateau in Concho County. The lower part of
these hills are composed of a narrow band of limy
sediment of the Antlers Sand Formation. Real soilsformed below the limestone scarps and along foot
slopes in the loamy material of the basal Cretaceous
(Antlers Sand). The Segovia Formation is in the south
and southwest part of the county and also consists of
alternating beds of limestone and marl. The Eola, Kavett,
Oplin, Tarrant, and Valera soils formed over limestones
of the Fort Terrett and Segovia Formations.
Loamy and clayey material of the Quaternary system
was deposited in valleys, on high terraces, and on
upland plains over extensive areas in Concho County.
The Angelo, Cho, Karnes, Lipan, Mereta, Miles, Nuvalde,
Rowena, Sagerton, and Tobosa soils formed in this
material. The Cho soils formed in the most calcareous
and most gravelly outwash, and Tobosa soils formed in
the most clayey outwash. The parent material of soils on
flood plains of streams consists of recent deposits of
alluvium. The Dev, Frio, Gageby, Rioconcho, and Yahola
soils formed in these deposits and are moderately
alkaline.
Plant and Animal Life
Plants, animals, earthworms, insects, bacteria, and
fungi have contributed to the development of soils. The
mixed prairie grassland contributes large amounts of
organic matter and organic acids that help to weather
the parent material and reduce erosion. When the roots
of grasses and trees decay, they leave a network of
channels and pores that increase the passage of air and
water through the soil. Burrowing by earthworms and
termites increases porosity by leaving open channels for
the movement of water and air into the soil. Earthworms
also help distribute organic matter to deeper parts of the
soil through their castings. Micro-organisms help to
decompose organic matter, release nutrients, and add
nitrogen to the soil.
At one time there were millions of prairie dogs
throughout this area. They burrowed deep down into the
caliche and brought highly calcareous soil material to the
surface. Tree roots are now able to grow much deeper
through these old filled-in burrows, especially in shallow
soils, such as the Cho and Mereta soils.
Climate
The climate of Concho County is dry, subhumid, and
fairly uniform. It has had a definite effect on soil
formation. Rainfall, evaporation, temperature, and wind
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General Soil Map, Concho County, Texas (Map)
Map displays soil types along with creeks, towns, schools, churches, power transmission lines, oil and gas pipelines, roads, and railroads. Includes legend and symbols. Scale 1:253,400
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Clower, Dennis F. Soil Survey of Concho County, Texas, book, 1988; Washington D.C.. (https://texashistory.unt.edu/ark:/67531/metapth130209/m1/75/?q=tex-land&rotate=90: accessed July 16, 2024), University of North Texas Libraries, The Portal to Texas History, https://texashistory.unt.edu; crediting UNT Libraries Government Documents Department.