Land

The major physiographic regions of Texas include the Gulf Coastal Plain in the east and southeast; the North Central Plains, covering most of central Texas; the Great Plains, extending from west-central Texas up into the panhandle; and the mountainous trans-Pecos area in the extreme west.

Within the Gulf Coastal Plain are the Piney Woods, and the Post Oak Belt, a flat region of mixed soil that gives way to the rolling prairie of the Blackland Belt which is  the state's most densely populated region. The Balcones Escarpment (so-called by the Spanish because its sharp profile suggests a balcony), a geological fault line running from the Rio Grande near Del Rio across central Texas, separates the Gulf Coastal Plain and Rio Grande Plain from the North Central Plains and south-central Hill Country. It also divides East Texas from West Texas.

The North Central Plains extend from the Blackland Belt to the Cap Rock Escarpment, a natural boundary carved by erosion to heights of nearly 1,000 ft (300 m) in some places. The mineral-rich Burnet-Llano Basin are also found here. West of the Cap Rock Escarpment are the Great Plains, stretching north–south from the Panhandle Plains to the Edwards Plateau, just north of the Balcones Escarpment.

The highest point of the state, Guadalupe Peak with an altitude of 8,749 ft (2,668 m) lies between the Pecos River and the Rio Grande.

Texas boasts of a few natural lakes which include Caddo Lake, which lies in Texas and Louisiana, the state's largest natural lake. Two artificial reservoirs—Amistad (shared with Mexico), near Del Rio, and Toledo Bend (shared with Louisiana) on the Sabine River—have respective storage capacities exceeding 3 million and 4 million acre-ft, and the Sam Rayburn Reservoir (covering 179 sq mi/464 sq km) has a capacity of 2.9 million acre-ft.

One reason Texas has so many reservoirs is that it is blessed with a number of major river systems, although none is navigable for more than 50 mi (80 km) inland. Rio Grande is the nation's 2nd-longest river, exceeded only by the Missouri-Mississippi river system. The Colorado River is the longest river wholly within the state, extending about 600 mi (970 km) on its journey across central and southeastern Texas to the Gulf of Mexico. Other important rivers include the Nueces, San Antonio, the Brazos, the Trinity, the San Jacinto, the Neches, the Sabine, the Red, and the Canadian, which crosses the Texas panhandle from New Mexico to Oklahoma, bringing moisture to the cattle raisers and wheat growers of that region. In all, Texas has about 3,700 identifiable streams, many of which dry up in the summer and flood during periods of rainfall.

Because of its extensive outcroppings of limestone, extending westward from the Balcones Escarpment, Texas contains a maze of caverns. The most popular ones are Longhorn Cavern in Burnet County; Wonder Cave, near San Marcos; the Caverns of Sonora, at Sonora; and Jack Pit Cave, in Menard County, which, with 19,000 ft (5,800 m) of passages, is the most extensive cave yet mapped in the state.