The amazing view you see before you is a result of tectonic
activity in Big Bend park related to the Paleozoic Marathon
orogeny. The Marathon orogeny (part of the Ouachita-Marathon-Sonora
orogenic belt) is part of thrusting of rocks from the South
American Plate over the North American Plate. This can be best seen
in the Persimmon Gap area of the park. This orogenic event is
linked to the lack of Triassic- and Jurassic-age rocks in the park.
Between the Triassic and the Cretaceous the South American Plate
rifted from the North American Plate, resulting in the deposition
of the Glen Rose Limestone, Del Carmen Limestone, Sue Peaks
Formation, Santa Elena Limestone, Del Rio Clay, Buda Limestone and
Boquillas formations (preserved in the Sierra del
Carmen–Santiago Mountains, Nine Point Mesa, Mariscal Mountain
and Mesa de Anguila areas).
Also during this time, the Chihuahua trough formed as the Gulf
of Mexico opened, which resulted in east-west striking normal
faulting. As a result of this depositional time, there are
dinosaur, forest, and other fossils preserved in the park.
Following the ending of rifting in the Late Cretaceous to the early
Tertiary, the Big Bend area was subjected to the Laramide orogeny.
This period of compression caused the northeast-facing Mesa de
Anguila (an uplifted monocline on the southwest margin of the
park), the southwest-facing Sierra del Carmen–Santiago
Mountains (an uplifted and thrust-faulted monocline that forms the
boundary of the park on the east) and the Tornillo Basin.
During the middle Tertiary most of the volcanic rocks, including
the Chisos group, the Pine Canyon caldera complex and the Burro
Mesa Formation, formed. The most recent tectonic activity in the
park is Basin and Range faulting from the late Tertiary to
Quaternary.
This period of east-west extension has resulted in Estufa and
Dehalo bolsons in the Chisos Mountains, as well as the Terlingua
and Sierra del Carmen, Chalk Draw and Burro Mesa faults.
You are looking toward the Santa Elena Canyon into Mexico.
This vista is named for the surrounding daggerlike plants in
this area called Sotol.
To claim credit for this earthcache.....
1. Which of the landforms that you see before you do you think is
the result of erosion?
2. Which of the landforms that you see before you do you think
is the result of volcanic activity?
3. What part do you think that weathering has played in the
formation of these mountains?
4. According to the sign, on what important area does Burro Mesa
sit?
5. Brownie points for photos, although this is not mandatory.