Reconnoissance soil survey of South Texas Page: 41 of 115
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RECONNOISSANCE SOIL SURVEY OF SOUTH TEXAS. 39
separation between the Duval and Zapata soils in this county is very
arbitrary, the agricultural value of the two being low here and the
country difficult to get over, so a detailed separation was impracticable.
Some small areas of Zapata loam are also included, especially
in the western part of Webb County.
Native vegetation.-The vegetation varies with the depth to the
underlying rock. On the hills and ridges, where this is usually near
the surface, it is principally chaparral, guajillo, and cactus, while on
the lower slopes and in the valleys mesquite and cactus are more in
evidence. The agricultural value follows very closely this change in
Utilization.-This is distinctly a grazing type and should be
devoted to this purpose. The hilly character of the topography
makes irrigation impracticable, even if water were obtainable, except
on a few small areas in the valley, which are really the Brennan fine
sandy loam, although they are not shown in the map. None of it is
cultivated at the present time and probably very little will be for
many years. Much of it is so hilly and either so stony or has the
limestone so near the surface that it can never be used for farming.
While it does not support enough native grass to make a first-class
grazing soil, it is better suited to this purpose than any other. In
Duval County a number of cattle ranches are located on this type,
and a few are found in other areas where this soil occurs, but the
latter sections are more given to sheep raising. Wells are very
scarce, and in most sections rain water collected in surface "tanks"
must be depended upon.
Description.-The first 6 to 10 inches of the Zapata loam is a light
gray to grayish-brown loam and is underlain by a slightly heavier
loam of a gray to yellowish-gray or slightly pinkish color. Sandstone
or limestone is usually encountered at a depth of less than 3 feet
and these sometimes outcrop on the steeper slopes. The sand content
of the soil being rather fine, and the percentage of clay not very high,
the soil is not as coherent as might be expected in a loam. There is
often found a very light-colored surface crust, but this is easily broken
up. There is no distinct line between soil and subsoil, the change
taking place gradually as the depth increases. This type is very low
in humus, but contains a rather large percentage of lime.
Origin.-The soil is formed from thin deposits of loam over the
sandstones. In some cases these have apparently had some influence
upon the character of the soil. The formation is probably Lafayette
and represents material laid down during the slackening of the waters.
Location.-The Zapata loam does not cover an extensive stretch of
country and is found principally upon the tops of the hills northeast
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Map displays soil types along with arroyos, lakes, rivers, swamps, counties, towns, roads, railroads, and ranches. Includes legend and soil profiles.
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Coffey, George Nelson. Reconnoissance soil survey of South Texas, book, June 16, 1910; Washington D.C.. (texashistory.unt.edu/ark:/67531/metapth19753/m1/41/: accessed June 24, 2018), University of North Texas Libraries, The Portal to Texas History, texashistory.unt.edu; crediting UNT Libraries Government Documents Department.