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The Edwards Plateau is the bottom part of the Great Plains in Texas and are bordered on the south and east by the Balcones Fault, a geological line in Texas running east from Del Rio, through San Antonio, Austin and curving northward through the east side of Dallas. This geological line has the surface expression of the Balcones Escarpment consisting of cliffs and cliff-like structures.
Balcones Escarpment
This escarpment forms the southernmost and easternmost boundary of the Great Plains in the area of the Edwards Plateau, an area also call by the name Texas Hill Country. Below the Edwards Plateau at the bottom of these cliffs are the Texas Coastal Plains. The coastal plains in Texas extend southward and eastward to the Gulf of Mexico.
Balcones Fall Zone
The Balcones Fall Zone, also called the Fault Zone or Fall Line, is the area where an upland region and a coastal plain meet and is noticeable especially where rivers cross it, with resulting rapids or waterfalls. The uplands are relatively hard crystalline basement rock, whereas the coastal plain are softer sedimentary rock. A fall line often will recede upstream as a river cuts out the uphill dense material, forming "c-shaped" waterfalls and exposing bedrock shoals.
Because of these features, riverboats typically cannot travel any farther inland without portaging, unless locks are built. The rapid change of elevation of the water and resulting energy release make the fall line a good location for water mills, grist mills, and sawmills. Seeking a head of navigation with a ready supply of water power, people have long made settlements where rivers cross a fall line.
Too, the Balcones fall line is a demarcation line for certain ecological systems and species distributions.
Fault Risk
The Balcones Fault is one of the lowest risk zones on the North American continent and is believed to have been inactive for about 15 million years, with the last activity during the
Miocene epoch.
Further, it is believed that the Balcones fault zone may have been a southwestern extension of the
Ouachita Mountains in Oklahoma, but have long since been buried under thousands of feet of sediment.
Subterranean features such as caves and springs (see the lists below) are numerous along the Balcones fault zone. Many cities are located on or near the Edwards Plateau, most likely because the Balcones fault zone has numerous locations for spring water.
History:
Probably the most famous of all the historical trails that cross near the Balcones Escarpment is the Spanish Colonial trail known as El Camino Real
de Los Tejas, which during that colonial time, the path followed the many water sources that were provided by the numerous springs just below the escarpment. (see The Steps below.)
The Ancients
Cascade Caverns, 29.7634900, -98.680245
Kickapoo Caverns, 29.610379, -100.452502 (Stuart Bat Cave)
Longhorn Caverns, 30.684630, -98.350930
Natural Bridge Caverns, 29.692697, -98.342693
Caves of Sonora, 30.555224, -100.811931
Inner Space Cavern, 30.607991, -97.687935
Cave Without a Name, 29.886169, -98.618351
Blue Hole, 30.003204, -98.090622
San Marcos Spring, 29.894677, -97.930275
San Marcos Spring Lake, 29.892910, -97.930390
Barton Spring, 30.263508, -97.772106
Salado spring, 30.943653, -97.536557
Jacob′s Well Natural Area, 30.039080, -98.126319
The Steps
Steps Afoot
Steps Afield
El Camino Real
de Los Tejas
The Appendixes
Hill Country Natural Area, 29.627964, -99.181252
Inks Lake State Park, 30.737363, -98.368591
Lost Maples State Natural Area, 29.807732, -99.570521
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