Forty-two years ago, I spent 10 weeks in the Eagle Mountains of Hudspeth County, in Trans Pecos, Texas. The purpose was working on my Master's Thesis Project (1978 - 1980). When I did that summer of fieldwork, I expected there to be other protracted visits and probably a 1979 field season. But the project was truncated by "life events" (primarily my 1979 crashed-and-burned love affair) and my (sometimes) ill-chosen reactions. But enough of that. It's time to use the experiences, regrets, and photos as "educational resources".
Except for a small "corner" of the SE quadrant, the rest of the Eagle Mountains (as far as I know) was part of the Eagle Mts. Ranch. That "small corner" needed to be traversed each time we went around the south end of the mountains to access Dan's field area. So, we had to ask around and travel further south along the edge of Eagle Flat to seek permission to cross, from the adjacent Eagle Mts. Ranch. As the rancher wasn't used to impromptu visitors, amidst his several barking dogs, when we emerged from my truck, he emerged from his trailer, shotgun-in-hand (but not in a threatening way).
After we explained that we were UTEP grad students and that we had open permission to explore the adjacent Eagle Mts. Ranch, he relaxed and smiled and the friendly banter began. He was pleased that we had the manners and decency to ask permission. [Due to the remoteness, we probably could have crossed his property multiple times without notice, but if caught, who knows what sort of hassles would have befallen us.]
For this 10-week period (approx. late-May to mid-July), this 1976 Jeep pickup (Figure 1) was my home (though I did keep my El Paso apartment). (Dan had his own tent.) Due to the mountain terrane demanding almost full-time 4-wheel drive in first gear (10 mph average), gas mileage was horrid. That being the case, I kept a couple of 5-gallon gas cans stashed under a couple of scavenged sheets of tin.
Usually, the gas would start to be depleted and the ice for food and beer storage would be gone every 4 or 5 days, depending on the temps and cloud cover. So we would journey into Van Horn to replenish needed supplies and eat in an actual restaurant, perhaps pay a short visit to a local tavern. Then back to East Mill (Figure 2) we would go.
[Perhaps ever two or three weeks, we would return to El Paso to report to our Thesis Advisor and check our mail and apartments' status (I had neighbors keeping-an-eye on mine.)]
[Perhaps ever two or three weeks, we would return to El Paso to report to our Thesis Advisor and check our mail and apartments' status (I had neighbors keeping-an-eye on mine.)]
Figure 1. (Before I had my Texas tag.)
Figure 2. East Mill.
Different classifications can be used for the Eagle Mts., e.g., Trans-Pecos Texas Volcanic Field, Basin and Range Province, Chihuahuan Desert, as well as generalized regional biome descriptions, e.g., Temperate Desert Creosote Bush/Mesquite Biome. (Regional Biomes are usually identified by Climate and dominant Plant(s).)
Unlike the 1977 and 1979 field trips or job sites, in 1978 my camera decided not to malfunction, so any flaws are due to 40 years of storage in alternating dusty, dry settings, then humid, sometimes musty basements (my bad).
Figure 3. Pyroclastic Breccia.
Figure 4. Weathered Pyroclastic Breccia.
Figure 5. (Labeled for educational use.)
For those unfamiliar with Caldera-type "Supervolcanoes", their circular to semi-circular crater diameters generally measure in the tens-of-kilometers and they have "long lives". Before any eruptions break through, their underlying magma chambers have "domed" (uplifted) an area measuring tens to hundreds of square kilometers. In the case of the Eagle Mts., the regional uplift (followed by one or more large crater-forming events) left a rim of (primarily) Cretaceous sedimentary rocks.
Brief examinations of the existing Eagle Mts. geologic map suggested that a half-mile long block of Cretaceous sedimentary rocks "broke loose" from the rim and "slid" into the open caldera. The presence of fluorite and the prospecting of other mineral resources, on the west side of the mountains, suggested interactions between heated volcanic fluids and the adjacent sedimentary rocks, especially limestones.
Another brief discovery - that I failed to follow-up upon - was in the "shotgun owner's" parcel. One day while doing a drive-through on one of the roads, I stopped to do a "lookabout" (with more purpose than a simple "walkabout"). As this was just early reconnaissance, I only picked up a single hand-sample of an unusual rock (Figures 6A, 6B, 6C ).
The crude-bedding and suspected low-angle impact structures, as well as the lithologic-texture, suggest this might be a "Volcanogenic Siltstone". In the context of the long-life of a Caldera, a small lake receiving reworked ash might produce a siltstone. The small impact clasts may be small broken phenocrysts, "launched" during a local, minor ash eruption. On the basis of this Hypothesis, if correct, this could be an example of a sedimentary rock deposited inside a volcano.
When I did use this sample in Physical Geology Labs, I did so in a way to get students to think about "the possible", as I explained my Hypothesis.
(Forgive any lack of clarity and the lack of a scale, I wanted to get these posted tonight.)
Figure 6A.
Suspected "Volcanogenic Siltstone", crude layering can be seen on left side. On top layer are two small suspected low-angle impact structures.
Figure 6B.
Figure 6C.
Regrets
Not immediately recognizing and following-up on the "Volcanogenic Siltstone". I wish that I had gone back and collected more samples and sought to identify the marginal contacts of the presumed lake sediments. Even though my participation in the project ended, it might have made an interesting geo-footnote for the person that took it over.
On that note, with 1979 being the personal train-wreck it was, I regret dropping out of school for several years. I also regret not offering any help to my compadres, in the field area, beyond what I did in the Summer of 1978. [But if things didn't unfold the way they did, I might not have met my first wife Marla and adopted a daughter and a son along the way. Sometimes, it's best to leave the "What ifs ... " alone.]
I also regret not making (or asking for) xerox copies of the 3 Master's Theses and 1 Doctoral Dissertation on the Eagle Mts. I couldn't foresee someday, decades later, being nostalgic for the place.
A few "orphan photos", the scanned slides of which I failed to label, as I should have. I suspect these are in the NE quadrant of the Eagle Mts., but I am not sure.
Figure 7.
Figure 8.
I think this peak is called "Black Top". As you can see, the volcanics sit atop a Syncline (presumably Cretaceous rocks). Figure 10 is another angle of this peak.
Figure 9.
Figure 10.
Another angle view of "Black Top", showing a good illustration of Talus Slopes.
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