From Lajitas to the Cuevas Amarillas Locale, Part 8: Essay in Black, Brown, and Yellow | Big Bend Ranch State Park, Texas, USA

Taken along the main park track, about 2.2 road mi / 3.5 km to the southeast of the turnoff to the Rancho Viejo Campground.

Now I’m far from the Rio Grande, having turned off the paved FM 170 and onto the dirt road past Redford that leads north and then east to the Solitario. I’ve already covered that amazing feature in a separate album. Here I discuss another fascinating locale that one comes across on the way there.

This other point of interest is the Cuevas Amarillas (“Yellow Caves”) archaeological site. Here’s my first good look at it and its environs. On the right is a butte, unnamed as far as I can tell. My main source for disambiguating the geology is once again Christopher D. Henry's Geologic Map of Big Bend Ranch State Park. I have praised this painstakingly detailed resource before, but in the case of this particular landform, the rock- unit labeling is not completely unequivocal. The space around the place, on the map that is, is just too cramped to put in every symbol, however necessary to understanding.

But this is what I infer. From top to bottom, the butte is quite an assortment of units of the Oligocene Rawls Formation:

- a resistant cap of porphyritic basalt lava of the Alazan Lava Member;

- conglomerate and coarse sandstone of the Segundo Lavas Member;

- trachyte lava of the Sauceda Lavas Member;

- porphyritic basalt of the Sauceda Lavas Member;

- debris-flow deposits of the Leyva Canyon Member.

That might strike you as nothing more than a laundry list of meaningless names, but to the geologist unblinkered by a hyperspecialist STEM education, it’s a first-rate screenplay in which a series of dramatic episodes unfold: erupting volcanoes spewing forth lobes of molten rock, one after the other, some 28 Ma ago.

It's the far side of the road, however, that is the real focal point for the rest of this series. There stands a much lower butte that’s tinted a golden yellow rather than brown and black. That coloration indicates that it is made of a much different volcanic rock type, the Rancho Viejo Tuff Member of the Rawls Formation. It’s there, in its recesses and under its overhangs, that ancient American Indians left signs of their habitation, including fabricated depressions in the stone that served as grain-grinding mortars.

We’ll take a closer look at all that in the posts to follow.

To see the other photos and descriptions in this series, visit my From Lajitas to the Cuevas Amarillas Locale album.

Taken on: January 2, 2000

Tags:

archaeology

geology

parks

nature

rock

rocks

stone

Texas

Trans-Pecos Texas

Big Bend Ranch State Park

Cuevas Amarillas

Rawls Formation

basalt

trachyte

tuff

Rancho Viejo Tuff Member « less

Sets appears in: • From Lajitas to the Cuevas Amarillas Locale | Big Bend Ranch State Park, Texas • Mountains & Hills; Mesas & Buttes; Hogbacks, Cuestas, & Flatirons more » • Natural History: Big Bend Region & All of Trans-Pecos Texas • Ortsinn: Landscapes & Localities • Rock Forms, Rock Formations « less

Camera: MAKER NAME 96660, f/1.8, 1/28 sec, 2.8mm, ISO 50 (more info) (hide info)

Camera:	MAKER NAME 96660
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Focal Length:	2.8mm
ISO:	50
Exposure Bias:	0 EV
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