Texas Almanac, 1990-1991 Page: 70
611 p. : col. ill., maps, ports. ; 23 cm.View a full description of this book.
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70 TEXAS ALMANAC 1990-1991
ENVIRONMENTN
50 Al.NATURAL REGIONS
OF TEXASPhysical Features
Texas is at the crossroads of five major physiographic regions of North America: the Gulf Coastal Plain; the Great
Plains; the Interior Lowlands; the Rocky Mountain System; and the Basin and Range Province.
A special thanks to Dr. William M. Holmes, chairman of the Department of Geography at North Texas State
University, for his assistance in revising this section.Physical Regions
Principal physical regions of Texas usually are listed
as follows: (See also Plant Life and Soils.)
THE GULF COASTAL PLAINS
Texas' Gulf Coastal Plains are the western extension
of the coastal plain extending from the Atlantic to be-
yond the Rio Grande. Its characteristic rolling to hilly
surface covered with a heavy growth of pine and hard-
woods extends into East Texas, but in the increasingly
arid west its forests become secondary in nature, consis-
ting largely of post oaks and, farther west, prairies and
brush lands.
The interior limit of the Gulf Coastal Plains in Texas
is the line of the Balcones Fault and Escarpment. This ge-ologic fault or shearing of underground strata extends
eastward from a point on the Rio Grande near Del Rio. It
extends to the northwestern part of Bexar County where
it turns northeastward and extends through Comal, Hays
and Travis counties, intersecting the Colorado River
immediately above Austin. The fault line is a single, defi-
nite geologic feature, accompanied by a line of south-
ward- and eastward-facing hills. The resemblance of the
hills to balconies when viewed from the plain below
accounts for the Spanish name, balcones. North of Waco,
features of the fault zone are sufficiently inconspicuous
that the interior boundary of the Coastal Plain follows
the traditional geologic contact between upper and low-
er Cretaceous rocks. This contact is along the western
edge of the Eastern Cross Timbers.
This fault line is usually accepted as the boundary
between lowland and upland Texas. Below this fault line
the surface is characteristically coastal plains. Above
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Kingston, Mike. Texas Almanac, 1990-1991, book, 1989; Dallas, Texas. (https://texashistory.unt.edu/ark:/67531/metapth162512/m1/72/: accessed April 26, 2024), University of North Texas Libraries, The Portal to Texas History, https://texashistory.unt.edu; crediting Texas State Historical Association.