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Geological History of Big Bend National Park

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Pine Canyon Falls inside Big Bend National Park.

Pine Canyon Falls inside Big Bend National Park. (Photo credit: Wikipedia)

Big Bend National Park is a dream of a place to study geological history. Sparse vegetation and plenty of recent erosion ensures clearly exposed rocks meaning that you can find evidence of everything from landslides, to volcanoes, to flash floods and fossils.

The oldest rocks at Big Bend National Park have been aged as being around 500 million years old, which means that there’s plenty of geolocial history to go at. The oldest rocks are at Persimmon Gap which are actually the remains of the Ouachita Mountains which once stretched all the way from Big Bend to Arkansas.

During the Cretaceous Period, around 135 million years ago the whole area was covered by a shallow sea, much of the limestone which is found at Big Bend National Park came from this sea bed. Mariscal Canyon, Santa Elena Canyon, Boquillas Canyon plus the Dead Horse Mountains are all made of limestone from this period, you can also find loads of fossils within these rocks, lots of different types of fossils from giant clams, fish, crocodiles and turtles, as well as loads of different types of dinosaurs.

Moving on a few million years to around 42 million years ago there was volcanic activity beginning in the area of Christmas Mountains, 38 million years ago Sierra Quemada, in Big Bend National Park became active, so what does that lead you to . . . . deposits of ash and lava creating the majority of the Chisos Mountains. In some areas of Big Bend National Park the magma didn’t even reach the earths surface and simply cooled beneath the ground, these extremely hardened chambers becoming exposed by erosion over time. A few examples of this type of feature include Grapevine Hills, Maverick Mountain and Nugent Mountain.

As the fault lines were routinely sunk and uplifted the shape of the park landscape was created, much of it still being visible to this day. The Sierra del Carmens and Mesa de Anguila, for example, were formed as a result of the land sinking to reveal them, as well as sunken blocks of land which were filled with eroded materials forming flat basins like Tornilla Flat.

It might surprise you to know that water even erodes rocks in the desert . . . exactly the places you don’t expect to find any water. Okay, so maybe they don’t exactly experience regular rainfall, but flash floods and run-off continually reshape new rocks, limestone dissolves in water, and the Rio Grande then carries away the sediment. In fact, there is so much sand being carried down the river that you can often hear it scraping along the walls of the canyon like sandpaper, constantly carving out the canyons until they become deeper and deeper.

Big Bend National Park is constantly changing, but as Heraclitus, the Greek philosopher once said “There is nothing permanent except change” – I don’t think he was specifically talking about Big Bend National Park, but he might as well have been . . . every time you visit Big Bend National Park it you be a different place, the landscape changes every single day.

Okay, so the quality of the video isn’t great, but you can still see the layers pretty clearly.

 

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