Moseying Up the Permian Reef Geology Trail, Part 10: Grokking the Grottos | McKittrick Canyon Locale, Guadalupe Mountains National Park, Texas, USA

Looking northwestward and up the path at the locale known as the Grottos.

This is Stop 4, as described in one of my main sources for this album, the Texas Bureau of Economic Geology Guide to this trail.

On the day I brought a tour group here the National Park Service maintenance crew had failed to rake out and grade the trail and put down nonskid rubber matting for us.

No, I'm not really that entitled, though I've certainly had students and for that matter tour participants who are. The point here is that this photo shows the trail as it is to be expected. It's nicely trimmed with all sorts of spiny and thorny vegetation and features every size and shape of limestone pebble and cobble imaginable. Don't attempt this one in your flip-flops.

However, this spot is one of the places along the way that makes the effort all worthwhile. As I discovered on this sunny day, it's just about the only shady rest along the track, and if you haven't slathered on a lot of sunblock beforehand, your exposed skin can get painfully burned.

The trail actually threads through the narrow gap between the double-domed bedrock tower at left and the cliff. At an altitude of about 5,360 ft / 1,634 m we have already climbed about 350 ft / 107m from the bed of McKittrick Draw, but we're still on the toe of the reef slope. And all the rock ahead of us belongs to the Lamar Limestone Member of the Permian Bell Canyon Formation.

If you're geologically inclined and interested in learning some in-depth carbonate petrology, the TBEG guide cited above has an excellent diagram and detailed description. Go to this page of the guide and scroll down to Stop 4. There you'll see how the tower has been lovingly subdivided into different types of packstone and wackestone, though yakstone and quackstone sensu Wiggers seem to be lacking.

One of the most interesting aspects of the tower's lithology is found near its base, were the rock narrows into a sort of neck. (It's best seen in this photo under a click or two of magnification.) This section contains a surface that has been interpreted as a glide plane. In other words, it was a tilted bedrock slope that other masses of rock slid down when this sundrenched desert environment still was a saltwater sea and the reef above us was flourishing.

You'll find the other photos and descriptions of this series in my Moseying Up the Permian Reef Geology Trail album.

Taken in: United States / Texas / Nickel Creek Station (show map)

Taken on: March 10, 2002

Tags:

geology

landscape

parks

rock

rocks

stone

Texas

Trans-Pecos Texas

Guadalupe Mountains National Park

The Grottos

Permian Reef Geology Trail

McKittrick Canyon

Lamar Limestone Member

national parks

Bell Canyon Formation

ancient reefs

wackestone

packstone « less

Sets appears in: • Moseying Up the Permian Reef Geology Trail, Guadalupe Mountains National Park, Texas • Natural History: Big Bend Region & All of Trans-Pecos Texas more » • Ortsinn: Landscapes & Localities • Rock Forms, Rock Formations « less

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

Camera:	MAKER NAME 96660
Aperture:	f/1.8
Exposure Time:	0.02 sec (1/50)
Focal Length:	2.8mm
ISO:	50
Exposure Bias:	0 EV
Flash:	Auto, Did not fire
Exposure Program:	Program AE
Metering Mode:	Average
White Balance:	Auto
Color Space:	Uncalibrated
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