Balcones Fault Zone is a tensional structural
system in Texas (USA) that runs
approximately from the southwest part of the state near Del Rio, Texas to the north central region near Waco, Texas along Interstate
The Balcones Fault zone is made up of many smaller
features, including normal faults
, and horsts
. One of the most obvious features is the
location of the fault zone may be related to the Ouachita
Mountains, formed 300 million years ago during a continental
Although long-since eroded away in Texas, the
roots of these ancient mountains still exist, buried beneath
thousands of feet of sediment
. These buried
Ouachita Mountains may still be an area of weakness that becomes a
preferred site for faulting when stress exists in the Earth's
. The Balcones Fault zone was
most recently active about 15 million years ago during the Miocene
epoch. This activity was related to subsidence of the Texas Coastal Plain, most likely from the large amount of sediment
deposited on it by Texas rivers.
The Balcones Fault zone is
not active today, and is in one of the lowest risk zones for
in the United States.
The surface expression of the fault is the Balcones Escarpment
, which forms the eastern boundary of
the Texas Hill Country
western boundary of the Texas Coastal Plain and consists of cliffs
and cliff-like structures. Subterranean features such as Wonder Cave
other smaller caves are found along the fault zone.
Many cities are located along this fault zone, and that is not a
coincidence. Frequently, springs such as San Pedro
Springs, Comal Springs, San Marcos Springs, Barton
Springs and Salado Springs are found in the fault zone and provide a source of
fresh water and an obvious place for human settlement.
The Balcones Fault Zone is a demarcation line for certain
ecological systems and species distributions. For example, the
California Fan Palm (Washingtonia filifera
) is the
only species of palm tree
that is native
to the continental United States west of the Balcones Fault.