Physical Regions of Texas
The principal physical regions of Texas are usually listed as follows:
I. Gulf Coastal Plains
Texas’ Gulf Coastal Plains are the western extension of the coastal plain extending from the Atlantic Ocean to beyond the Rio Grande. Its characteristic rolling to hilly surface covered with a heavy growth of pine and hardwoods extends into East Texas. In the increasingly arid west, however, its forests become secondary in nature, consisting largely of post oaks and, farther west, prairies and brushlands.
The interior limit of the Gulf Coastal Plains in Texas is the line of the Balcones Fault and Escarpment. This geologic 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 north of Austin. The fault line is a single, definite geologic feature, accompanied by a line of southward- and eastward-facing hills.
The resemblance of the hills to balconies when viewed from the plain below accounts for the Spanish name for this area: 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 lower Cretaceous rocks. This contact is along the eastern edge of the Eastern Cross Timbers.
This fault line is usually accepted as the boundary between lowland and upland Texas. Below the fault line, the surface is characteristically coastal plains. Above the Balcones Fault, the surface is characteristically interior rolling plains.
A. Pine Belt or “Piney Woods”
The Pine Belt, called the “Piney Woods,” extends 75 to 125 miles into Texas from the east. From north to south, it extends from the Red River to within about 25 miles of the Gulf Coast. Interspersed among the pines are hardwood timbers, usually in valleys of rivers and creeks. This area is the source of practically all of Texas’ commercial timber production(see Texas Forest Resources, page 107). It was settled early in Texas’ history and is one of the oldest farming areas in the state.
This area’s soils and climate are adaptable to the production of a variety of fruit and vegetable crops. Cattle raising is widespread, along with the development of pastures planted to improved grasses. Lumber production is the principal industry. There is a large iron-and-steel industry near Daingerfield in Morris County based on nearby iron deposits. Iron deposits are also worked in Rusk and one or two other counties.
A great oil field discovered in Gregg, Rusk, and Smith counties in 1931 has done more than anything else to contribute to the economic growth of the area. This area has a variety of clays, lignite, and other minerals as potentials for development.
B. Post Oak Belt
The main Post Oak Belt of Texas is wedged between the Pine Belt on the east, Blacklands on the west, and the Coastal Prairies on the south, covering a considerable area in East-Central Texas. The principal industry is diversified farming and livestock raising.
Throughout, it is spotty in character, with some insular areas of blackland soil and some that closely resemble those of the Pine Belt. There is a small, isolated area of loblolly pines in Bastrop, Caldwell, Fayette, and Lee counties known as the “Lost Pines,” the westernmost southern pines in the United States. The Post Oak Belt has lignite, commercial clays, and some other minerals.
C. Blackland Belt
The Blackland Belt stretches from the Rio Grande to the Red River, lying just below the line of the Balcones Fault and varying in width from 15 to 70 miles. It is narrowest below the segment of the Balcones Fault from the Rio Grande to Bexar County and gradually widens as it runs northeast to the Red River. Its rolling prairie, easily turned by the plow, developed rapidly as a farming area until the 1930s and was the principal cotton-producing area of Texas. Now, however, other Texas areas that are irrigated and mechanized lead in farming.
Because of the early growth, the Blackland Belt is still the most thickly populated area in the state and contains within it and along its border more of the state’s large and middle-sized cities than any other area. Primarily because of this concentration of population, this belt has the most diversified manufacturing industry of the state.
D. Coastal Prairies
The Texas Coastal Prairies extend westward along the coast from the Sabine River, reaching inland 30 to 60 miles. Between the Sabine and Galveston Bay, the line of demarcation between the prairies and the Pine Belt forests to the north is very distinct. The Coastal Prairies extend along the Gulf of Mexico from the Sabine to the Lower Rio Grande Valley.
The eastern half is covered with a heavy growth of grass; the western half, which is more arid, is covered with short grass and, in some places, with small timber and brush. The soil is heavy clay. Grass supports the densest cattle population in Texas, and cattle ranching is the principal agricultural industry. Rice is a major crop, grown under irrigation from wells and rivers. Cotton, grain sorghum, and truck crops also are grown.
Coastal Prairie areas have seen the greatest industrial development in Texas history since World War II. Chief concentration has been from Orange and Beaumont to Houston, and much of the development has been in petrochemicals and the aerospace industry.
Corpus Christi, in the Coastal Bend, and Brownsville, in the Lower Rio Grande Valley, have seaports and agricultural and industrial sections. Cotton, grain, vegetables, and citrus fruits are the principal crops. Cattle production is significant, with the famed King Ranch and other large ranches located here.
E. Lower Rio Grande Valley
The deep alluvial soils and distinctive economy cause the Lower Rio Grande Valley to be classified as a subregion of the Gulf Coastal Plains. “The Valley,” as it is called locally, is Texas’ greatest citrus and winter vegetable growing region because of the normal absence of freezing weather and the rich delta soils of the Rio Grande. Despite occasional damaging freezes, the Lower Valley ranks high among the nation’s fruit and truck-farming regions. Much of the acreage is irrigated, although dry-land farming also is practiced.
F. Rio Grande Plain
This area may be roughly defined as lying south of San Antonio between the Rio Grande and the Gulf Coast. The Rio Grande Plain shows characteristics of both the Gulf Coastal Plains and the North Mexico Plains because there is similarity of topography, climate, and plant life all the way from the Balcones Escarpment in Texas to the Sierra Madre Oriental in Mexico, which runs past Monterrey about 160 miles south of Laredo.
The Rio Grande Plain is partly prairie, but much of it is covered with a dense growth of prickly pear, mesquite, dwarf oak, catclaw, guajillo, huisache, blackbrush, cenizo, and other cactus and wild shrubs. It is devoted primarily to raising cattle, sheep, and goats. The Texas Angora goat and mohair industry centers in this area and on the Edwards Plateau, which borders it on the north. San Antonio and Laredo are its chief commercial centers, with San Antonio dominating trade.
There is some farming, and the Winter Garden, centering in Dimmit and Zavala counties north of Laredo, is irrigated from wells and streams to produce vegetables in late winter and early spring. Primarily, however, the central and western part of the Rio Grande Plain is devoted to livestock raising.
The rainfall is less than 25 inches annually, and the hot summers cause heavy evaporation, so that cultivation without irrigation is limited.
Over a large area in the central and western parts of the Rio Grande Plain, the growth of small oaks, mesquite, prickly pear (Opuntia) cactus, and a variety of wild shrubs is very dense, and it is often called the Brush Country. It is also referred to as the chaparral and the monte. (Monte is a Spanish word, one meaning of which is dense brush.)
II. Interior Lowlands
North Central Plains
The North Central Plains of Texas are a southwestern extension into Texas of the interior, or central, lowlands that extend northward to the Canadian border, paralleling the Great Plains to the West. The North Central Plains of Texas extend from the Blackland Belt on the east to the Caprock Escarpment on the west. From north to south, they extend from the Red River to the Colorado River.
A. West Texas Rolling Plains
The West Texas Rolling Plains, approximately the western two-thirds of the North Central Plains in Texas, rise from east to west in altitude from about 750 feet to 2,000 feet at the base of the Caprock Escarpment. Annual rainfall ranges from about 30 inches on the east to 20 inches on the west. In general, as one progresses westward in Texas, the precipitation not only declines but also becomes more variable from year to year. Temperature varies rather widely between summer’s heat and winter’s cold.
This area still has a large cattle-raising industry with many of the state’s largest ranches. However, there is much level, cultivable land.
B. Grand Prairie
Near the eastern edge of the North Central Plains is the Grand Prairie, extending south from the Red River in an irregular band through Cooke, Montague, Wise, Denton, Tarrant, Parker, Hood, Johnson, Bosque, Coryell, and some adjacent counties.
It is a limestone-based area, usually treeless except along the numerous streams, and adapted primarily to raising livestock and growing staple crops. Sometimes called the Fort Worth Prairie, it has an agricultural economy and largely rural population, with no large cities, except Fort Worth on its eastern boundary.
C. Eastern and Western Cross Timbers
Hanging over the top of the Grand Prairie and dropping down on each side are the Eastern and Western Cross Timbers. The two southward-extending bands are connected by a narrow strip along the Red River.
The Eastern Cross Timbers extend southward from the Red River through eastern Denton County and along the boundary between Dallas and Tarrant counties. It then stretches through Johnson County to the Brazos River and into Hill County.
The much larger Western Cross Timbers extend from the Red River south through Clay, Montague, Jack, Wise, Parker, Palo Pinto, Hood, Erath, Eastland, Comanche, Brown, and Mills counties to the Colorado River, where they meet the Llano Basin.
Their soils are adapted to fruit and vegetable crops, which reach considerable commercial production in some areas in Parker, Erath, Eastland, and Comanche counties.
III. Great Plains
A. High Plains
The Great Plains, which lie to the east of the base of the Rocky Mountains, extend into northwestern Texas. This area, commonly known as the High Plains, is a vast, flat, high plain covered with thick layers of alluvial material. It is also known as the Staked Plains or the Spanish equivalent, Llano Estacado.
Historians differ as to the origin of this name. Some say it came from the fact that the explorer Coronado’s expedition used stakes to mark its route across the trackless sea of grass so that it would be guided on its return trip. Others think that the estacado refers to the palisaded appearance of the Caprock in many places, especially the west-facing escarpment in New Mexico.
The Caprock Escarpment is the dividing line between the High Plains and the lower West Texas Rolling Plains. Like the Balcones Escarpment, the Caprock Escarpment is a striking physical feature, rising abruptly 200, 500, and in some places almost 1,000 feet above the plains. Unlike the Balcones Escarpment, the Caprock was caused by surface erosion.
Where rivers issue from the eastern face of the Caprock, there frequently are notable canyons, such as Palo Duro Canyon on the Prairie Dog Town Fork of the Red River, Blanco Canyon on the White River, as well as the breaks along the Canadian River as it crosses the Panhandle north of Amarillo.
Along the eastern edge of the Panhandle, there is a gradual descent of the land’s surface from high to low plains; but at the Red River, the Caprock Escarpment becomes a striking surface feature. It continues as an east-facing wall south through Briscoe, Floyd, Motley, Dickens, Crosby, Garza, and Borden counties, gradually decreasing in elevation. South of Borden County, the escarpment is less obvious, and the boundary between the High Plains and the Edwards Plateau occurs where the alluvial cover of the High Plains disappears.
Stretching over the largest level plain of its kind in the United States, the High Plains rise gradually from about 2,700 feet on the east to more than 4,000 in spots along the New Mexico border.
Chiefly because of climate and the resultant agriculture, subdivisions are called the North Plains and South Plains. The North Plains, from Hale County north, has primarily wheat and grain sorghum farming, but with significant ranching and petroleum developments. Amarillo is the largest city, with Plainview on the south and Borger on the north as important commercial centers.
The South Plains, also a leading grain sorghum region, leads Texas in cotton production. Lubbock is the principal city, and Lubbock County is one of the state’s largest cotton producers. Irrigation from underground reservoirs, centered around Lubbock and Plainview, waters much of the crop acreage.
B. Edwards Plateau
Geographers usually consider that the Great Plains at the foot of the Rocky Mountains actually continue southward from the High Plains of Texas to the Rio Grande and the Balcones 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 River. 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 River. Its upper boundary 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 and a varying 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.
The Hill Country is a popular name for the eastern portion of the Edwards Plateau south of the Llano Basin. Its notable large springs include Barton Springs at Austin, San Marcos Springs at San Marcos, Comal Springs at New Braunfels, several springs at San Antonio, and a number of others.
The Hill Country is characterized by rugged hills with relatively steep slopes and thin soils overlying limestone bedrock. High gradient streams combine with these steep hillslopes and occasionally heavy precipitation to produce an area with a significant flash-flood hazard.
C. Toyah Basin
To the northwest of the Edwards and Stockton plateaus is the Toyah Basin, a broad, flat remnant of an old sea floor that occupied the region as recently as Quaternary time.
Located in the Pecos River Valley, this region, in relatively recent time, has become important for many agricultural products as a result of irrigation. Additional economic activity is afforded by local oil fields.
D. 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 evidence there of a large number of minerals.
On the Colorado River in this area, a succession of dams impounds two large and five small reservoirs. Uppermost is Lake Buchanan, one of the large reservoirs, between Burnet and Llano counties. Below it in the western part of Travis County is Lake Travis.
Between these two large reservoirs are three smaller ones, Inks, L.B. Johnson (formerly Granite Shoals), and Marble Falls reservoirs, used primarily to produce electric power from the overflow from Lake Buchanan. Lake Austin is along the western part of the city of Austin. Still another small lake, Lady Bird Lake (formerly Town Lake), is formed by a low-water dam in Austin.
The recreational area around these lakes has been called the Highland Lakes Country. This is an interesting area with Precambrian and Paleozoic rocks found on the surface. Granitic domes, exemplified by Enchanted Rock north of Fredericksburg, form the core of this area of ancient rocks.
IV. Basin and Range Province
The Basin and Range province, with its center in Nevada, surrounds the Colorado Plateau on the west and south and enters far West Texas from southern New Mexico on the east. It consists of broad interior drainage basins interspersed with scattered fault-block mountain ranges.
Although this is the only part of Texas regarded as mountainous, these should not be confused with the Rocky Mountains. 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, bounded on the north by New Mexico and on the south by the Rio Grande, is distinctive in its physical and economic conditions. Traversed from north to south by fault-block mountains, it contains all of Texas’ true mountains and also is very interesting geologically.
A. Guadalupe Mountains
Highest of the Trans-Pecos Mountains is the Guadalupe Range, which enters Texas from New Mexico. It abruptly ends about 20 miles south of the boundary line, where Guadalupe Peak, (8,749 feet, highest in Texas) and El Capitan (8,085 feet) are situated. El Capitan, because of perspective, appears to the observer on the plain below to be higher than Guadalupe.
Lying just west of the Guadalupe Range and extending 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 dry during periods of low rainfall, exposing bottoms of solid salt; for years they were a source of commercial salt. West of the Hueco Mountains are the Franklin Mountains in El Paso, with the Hueco Bolson (a down-dropped area approximately 4,000 feet above sea level) separating the two fault-block ranges.
B. Davis Mountains
The Davis Mountains are principally in Jeff Davis County. The highest peak, Mount Livermore (8,378 feet), is one of the highest in Texas; there are several others more than 7,000 feet high. These mountains intercept the moisture-bearing winds and receive more precipitation than elsewhere in the Trans-Pecos, so they have more vegetation than the other Trans-Pecos mountains. Noteworthy are the San Solomon Springs at the northern base of these mountains.
C. Big Bend
South of the Davis Mountains lies the Big Bend country, so called because it is encompassed on three sides by a great southward swing of the Rio Grande. It is a mountainous 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, Mariscal, 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 remarkable topography and plant and animal life, the southern part of this region along the Rio Grande is home to Big Bend National Park, with headquarters in the Chisos Basin, a deep valley in the Chisos Mountains. It is a favorite recreation area.
D. Upper Rio Grande Valley
The Upper Rio Grande Valley, or 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 settlements of Ysleta, Socorro, and San Elizario, which were founded in the 1680s. Cotton is the chief product of this valley, much of it is the long-staple variety.
This limited area has a dense urban and rural population, in marked contrast to the territory surrounding it.
This article was reviewed by Dr. David R. Butler, Texas State University System Regents’ Professor of Geography at Texas State University–San Marcos.