Post #2

During the Paleozoic era , the Balcones Fault Zone was part of the ancient Ouachita rock structure. The area was covered by a sea that began to recede during the Pennsylvanian period, only to be covered again during the Cretaceous period when most of the parent sediment was deposited. The shale, limestone, and sandstone of the fault area reflect the various changes in the sea level.

The major movement along the fault occured between 27 and 12 million years ago, when the east sideof the fault was downthrown and the west upthrown. These faults created what is now known as the Texas Hill Country, with many grabens and horsts making the rolling landscape.

Taken from the top of another horst.

The Edwards Aquifer is also a result of the fault. The exposed more permeable limestone surrounded by the less permeable rock allows for fresh water to be held in the aquifer. The joints and fissures in the rock help the surface water travel down into the aquifer.

Me and my dad in front of escarpment

 The dissolving action of this ground water also creates sink holes and caves. The limestone solution creates caverns filled deposited limestone structures called karst.

Karst in cavern in Southwest Texas

A large sink hole above the aquifer

A sinkhole near Barton Springs

The composition of the rocks as well as human involvement like road cuts, lead to many different weathering processes, and to other weathered landforms.

 The vegetation seen at this road cut also aids in the weathering process through root wedging. The rocks show different rates of weathering as well, resulting in mass wasting by rock fall and the collection of talus at the base as well as cliff tops and ledges.


http://www.tpwmagazine.com/archive/2009/june/ed_2/index.phtml
http://water.usgs.gov/ogw/karst/aquifers/edwards/index