Texas Almanac, 1990-1991 Page: 73
611 p. : col. ill., maps, ports. ; 23 cm.View a full description of this book.
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ENVIRONMENT 73
reservoirs, centered around Lubbock and Plainview,
waters much of the crop acreage.
Edwards Plateau
Geographers usually consider the Great Plains at
the foot of the Rocky Mountains continuing southward
from the High Plains of Northwest Texas to the Rio
Grande and the Batcones Escarpment. This southern
and lower extension of the Great Plains in Texas is
known as the Edwards Plateau.
It lies between the Rio Grande and the Colorado Riv-
er. Its southeastern border is the Balcones Escarpment
from the Rio Grande at Del Rio eastward to San Antonio
and thence to Austin on the Colorado. Its upper bound-
ary is the Pecos River, though the Stockton Plateau is
geologically and topographically classed with the
Edwards Plateau. The Edwards Plateau varies from
about 750 feet high at its southern and eastern borders to
about 2,700 feet in places. Almost the entire surface is a
thin, limestone-based soil covered with a medium to
thick growth of cedar, small oak and mesquite with a va-
rying growth of prickly pear. Grass for cattle, weeds for
sheep and tree foliage for the browsing goats, support
three industries-cattle, goat and sheep raising-upon
which the area's economy depends. It is the nation's
leading Angora goat and mohair producing region and
one of the nation's leading sheep and wool areas. A few
crops are grown.
Toyah Basin
To the northwest of the Edwards and Stockton pla-
teaus is the Toyah Basin, a broad, flat remnant of an old
sea floor that occupied the region as recently as Quater-
nary time.
Located in the Pecos River Valley, this region, in rel-
atively recent time, has become important for many
agricultural products as a result of irrigation. Additional
economic activity is afforded by local oil fields.
The Hill Country
The Hill Country is a popular name for an area of
hills and spring-fed streams along the edge of the Bal-
cones Escarpment. It is popular with tourists who visit
the dude ranches and other attractions. Notable large
springs include Barton Springs at Austin, San Marcos
Springs at San Marcos, Comrnal Springs at New Braunfels,
several springs at San Antonio, and a number of others.
The Llano Basin
The Llano Basin lies at the junction of the Colorado
and Llano rivers in Burnet and Llano counties. Earlier
this was known as the "Central Mineral Region," because
of the evidence there of a large number of minerals.
On the Colorado River in this area a succession of
dams impounds two large and four small reservoirs.
Uppermost is Lake Buchanan, one of the two large reser-
voirs, between Burnet and Llano counties. Below it in
the western part of Travis County is Lake Travis. Be-
tween these two large reservoirs are three smaller ones,
Inks, L. B. Johnson (formerly Granite Shoals) and Marble
Falls reservoirs, used primarily for maintaining heads to
produce electric power from the overflow from Lake Bu-
chanan. Lake Austin is just above the city of Austin. Still
another small lake is formed by a low-water dam in Aus-
tin.
A name for this recreational area is the Highland
Lakes Country. Geologically this is an interesting area
with Precambrian and Paleozoic rocks found on the sur-
face.BASIN AND RANGE PROVINCE
The Basin and Range province, with its center in Ne-
vada, surrounds the Colorado Plateau on the west and
south and enters far West Texas from southern New
Mexico. It consists of broad interior drainage basins in-
terspersed with scattered fault-block mountain ranges.
Although this is the only part of Texas regarded as
mountainous, these should not be confused with the
Rockies. Of all the independent ranges in West Texas,
only the Davis Mountains resemble the Rockies, and
there is much debate about this.
Texas west of the Edwards Plateau is bounded on
the north by New Mexico and on the south by the Rio
Grande is distinctive in its physical and economic condi-
tions. Traversed from north to south by an eastern range
of the Rockies, it contains all of Texas' true mountains
and also is very interesting geologically.
Highest of the Trans-Pecos Mountains is the Guad-
alupe Range, which enters the state from New Mexico. It
comes to an abrupt end about 20 miles south of the
boundary line, where are situated Guadalupe Peak,
(8,749 feet, highest in Texas) and El Capitan (8,085 feet),
which, because of perspective, appears to the observer
on the plain below to be higher than Guadalupe and was
for many years thought to be the highest mountain in
Texas. Lying just west of the Guadalupe range and ex-
tending to the Hueco Mountains a short distance east of
El Paso is the Diablo Plateau or basin. It has no drainage
outlet to the sea. The runoff from the scant rain that falls
on its surface drains into a series of salt lakes that lie just
west of the Guadalupe Mountains. These lakes are
entirely dry during periods of low rainfall, exposing bot-
toms of solid salt, and for years they were a source of
commercial salt.
Davis Mountains
The Davis Mountains are principally in Jeff Davis
County. The highest peak, Mount Livermore, (8,206 feet)
is one of the highest in Texas. There are a number of
mountains more than 7,000 feet high. These mountains
intercept the moisture-bearing winds and receive more
precipitation than elsewhere in the Trans-Pecos. They
are greener with the growth of grass and forest trees
than the other Trans-Pecos mountains. Noteworthy are
the San Solomon Springs at the northern base of these
mountains.
Big Bend
South of the Davis Mountains lies the Big Bend coun-
try, so called because it is encompassed on three sides by
a great southward swing of the Rio Grande. It is a moun-
tainous country of scant rainfall and sparse population. Its
principal mountains, the Chisos, rise to 7,825 feet in Mount
Emory. Along the Rio Grande are the Santa Elena, Mars-
cal and Boquillas canyons with rim elevations of 3,500 to
3,775 feet. They are among the noteworthy canyons of
the North American continent. Because of its remarka-
ble topography, and plant and animal life, the southern
part of this region along the Rio Grande is home to the
Big Bend National Park, with headquarters in a deep val-
ley in the Chisos Mountains. It is a favorite recreation
area.
Upper Rio Grande Valley
The Upper Rio Grande (El Paso) Valley is a narrow
strip of irrigated land running down the river from El
Paso for a distance of 75 miles or more. In this area are
the historic towns and missions of Ysleta, Socorro and
San Elizario, oldest in Texas. Cotton is the chief product
of the valley, much of it long-staple variety. This limited
area has a dense urban and rural population in marked
contrast to the territory surrounding it.Geology of Texas
This article on the geology of Texas was prepared by the Bureau of Economic Geology at The University of Texas at
Austin.History in the Rocks
The fascinating geologic history of Texas is recorded
in rocks - both those exposed at the surface and those
penetrated by holes drilled in search of oil and natural
gas. The rocks reveal a dynamic, ever-changing earth -
ancient mountains, seas, volcanoes, earthquake belts,
rivers, hurricanes and winds. Today, the volcanoes and
great earthquake belts are no longer active, but rivers
and streams, wind and rain, and the slow, inexorable al-
terations of rocks at or near the surface continue to
change the face of Texas. The geologic history of Texas,
as documented by the rocks, began more than a billionyears ago; its legacy is the mineral wealth and varied
land forms of modern Texas.
Geologic Time Travel
The story preserved in the rocks requires an under-
standing of the origin of the strata and how they have
been deformed. Stratigraphy is the study of the composi-
tion, sequence and origin of the rocks: of what the rocks
are made, how they were formed and the order in which
the layers were formed. Structural geology reveals
the architecture of the rocks: the locations of the moun-
tains, volcanoes, sedimentary basins and earthquake
belts. Figure 1 is a map of rocks of various geo-
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Kingston, Mike. Texas Almanac, 1990-1991, book, 1989; Dallas, Texas. (https://texashistory.unt.edu/ark:/67531/metapth162512/m1/75/: accessed April 26, 2024), University of North Texas Libraries, The Portal to Texas History, https://texashistory.unt.edu; crediting Texas State Historical Association.