A day of enjoying great vistas and fascinating geology is often best celebrated with a good brew, and, fortunately, the trip to Terlingua through Study ("stoody") Butte features all of this. Actually, we drove to Terlingua after a trip down Maxwell Scenic Drive to Santa Elena Canyon, and the images in this section were not taken consecutively. Further, time and other constraints were such that I only have four images for this section. Hopefully, I will be able to flesh this section out in the future.
The first image below is of the Cretaceous Aguja Formation (pronounced something like "a-goo-ha" with a hard "h" and Spanish for "needle"), dipping slightly to the east. The Aguja is late Cretaceous in age and is largely composed of continental clay and sand deposits, although several hundred feet at the base of this formation are apparently marine in origin. Hence, the Aguja records a time in Big Bend's geological history when the sea left the land. Such an occurrence is called a regression. Penetrating the Aguja at this location - east of Croton Springs Road - is an igneous sill, where magma intruded the Aguja between bedding planes. The yellow color of the Aguja below the sill is similar to that in the second image below. Note that this yellow rock is largely overlain by gray-colored material derived from the erosion of the sill.
This second image is also of the Aguja, taken farther west on the other side of the intersection with Croton Springs Road. The yellowish sandstone at the top of this erosional remnant apparently acts as a cap rock to protect the gray shale beneath. You can look around in all directions, but this is the only feature that appears to remain in this area of this part of the Aguja. Once the sandstone finally succumbs to erosional forces, the clay will quickly disappear and all you will see, standing here and looking north, is flat terrain.
Like much of the desert floor, the surface around the erosional remnant (above) is windswept. Lighter material is driven off by the wind leaving the heavier gravel-size particles. This results in what is called desert pavement, which is ecologically important in that it protects the land from further wind erosion.
The image below was taken looking west toward Study Butte. An igneous intrusion forms Maverick Mountain to the left, while Dogie Mountain consists of Chisos volcanic rocks. An igneous sill appears along the ridge in front of Dogie Mountain. Note the ocotillo leafing out in the foreground. These weird plants look like pipe cleaners but put out beautiful red blooms earlier in the spring. By May, when this picture was taken, they begin to put out leaves, apparently in anticipation of the summer "monsoon" season, which is the wet season from Big Bend, south into the Chihuahua Desert of Mexico, and west into New Mexico and parts of Arizona. I've read where the ocotillo leafs out after even a light rain; however, there was no rain that I know of due to a prolonged drought prior to this picture. Possibly a stray shower occurred at this location.
When you finally get to Teringua, a former ghost town and site of the inter-galactically famous Terlingua Chile Cookoff, you can go into the store, grab a beer out of the fridge, pay the sweet young thing at the counter, and sit out on the porch with the locals (and a number of friendly dogs) for a fantastic view of the Chisos as the sun settles in the west. (Unfortunately, I was enjoying myself so much I forgot to snap a picture of the view. Another "to-do".)
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