Why The Rio Grande Is Where It Is

Part of the answer, but certainly not the whole answer, is “Because northern New Mexico and southern Colorado are where they are.” Enough elevation, enough precipitation, enough snowmelt at the sources of both the Rio Grande and its biggest tributary, the Pecos. If there is going to be net drainage, southeast is the obvious direction. I guess what I’m really wondering is, why aren’t there several Rio Grandettes? All originating in about the same place and all petering out well short of the Gulf of Mexico. Or, the same headwaters as the one we have now, only it splits repeatedly and fans out. True, West Texas isn’t as flat as central Louisiana is, but central and south Texas sure are, and I think there is room enough for what are known as distributaries.

It would be tedious – and not just for you – to review my travels and confirm my suspicion that I have been to every Texas county. There are 254 of 'em. Well, only a fraction are on the border, and I can see at once I’ve been to all of those. I do know I’ve been to, or at least through, in some cases at night, every Mexican state. Now, however, I can claim I’ve seen a lot of northern Tamaulipas, northern Nuevo León, northern Coahuila, and – at last, this past month – northern Chihuahua. And geography is about the same on either side! If, understandably, we only get enough water for 1.0 big rivers, why, amid so much flatness, is it here?

I still don’t know, but it was a pleasure following a 750-mile arc in a foreign country, and it has been a pleasure recalling such geology that I was treated to. This last trip, the overland part of it, I mean, ended when I boarded a plane in El Paso... and it was in that city, 35 years ago, that I got an impromptu tour and lecture. I was visiting a friend out there, and one afternoon his dad took us on a drive. I did not know – and had he not shown me, I might never have guessed – that El Paso is at one end of a rift. I had, of course, heard of the big-G, big-R one in East Africa, but never suspected these prodigies of plate tectonics were in America.

The other end of this feature is well north of El Paso, and to the limited extent I have researched, that is where most but not all of the geologizing has gone on. As for what happened downstream, or later, or both – was the Pecos already there where the Rio Grande meets it? - I am less certain. I do, however, recall something from 34 years ago: an introductory geology course at Texas Tech. I’d never taken any such course, and I still haven’t, dropping this one after a couple of weeks. But while I was in the room, I heard the professor mention his research interest, which was prehistoric lakes. I think that was the phrase he used. It hadn’t sounded very enchanting. But now I’m wondering. I thought I’d read – in the New York Times of all places, and maybe 33 years ago, ha! - that Texas has exactly one natural lake, and that straddles the Louisiana state line. All of the many others are manmade. If so, then where the heck were these old lakes, and where did they go, and how does anyone know?

If I’m looking up the right man, his research was more in the Panhandle than in the Valley, and concentrated on processes much closer to the present. But if there are any similarities, there could have been these wind-scoured basins which became – weather or perhaps climate permitting – pluvial lakes. 'Course, once it finally stopped raining and the sun came back out, and stayed out, the things would dry out. Now, whether the growing Rio Grande, as it bored its way gulfward, found its advance much facilitated whenever it reached one of these lakebeds, I do not know. But it’s possible.

On a bus ride, these can be entertaining thoughts. These Mexican buses, by the way, were very modern and comfortable. And I’m not just saying that because 44 years ago I rode Guatemalan ones that were old American school buses, standing for hours with livestock counted among the fellow passengers. At least the chickens went on the roof. The piglet, too, unless someone had it in his lap.

On this recent trip, as I plugged my phone into the USB port for recharging and leaned back and enjoyed the air conditioning, I had another idea that was unknown in all Latin America back then: At certain points along Highway 40 in Coahuila, I gazed at the verticality and recalled something I’d read in Michael Crichton’s posthumously published novel Dragon Teeth. The mountains hereabouts looked mostly like heaps of unsorted gravel, but on the brows of some of them, there were obvious strata, and I thought that in the book, as the professor of paleontology and his crew arrived in Montana, they saw the same things – and those were the keys to finding dinosaur fossils. Back home now, I find that I misremembered: what the professor did was point out, among many visible layers, those that were specifically Cretaceous, and if the light was right (and at that hour it was), bones positively bristled in the exposed rock. The boys marveled at this tuning of their sensibilities. Soon, they went on to unearth a lot of brontosaurus teeth. Well, I did no such thing in Coahuila! I don’t even know the antiquity of what I was seeing along the highway. But, again, it was so gratifying to find such stimulation here.

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Here’s a picture I took from that same bus as it sped from Monterrey to Torreón:

I was mainly interested in the fence, and even more interested in the signs that had appeared irregularly. They’d read Destruir el cercado amerita consignación. I am beginning to wonder if at least one of those words has some precise legal definition. If not, then I don’t know how threatening “Those who destroy fences deserve to be reported to the cops” can ever sound.

Whatever juridical forces are in play, beyond the fence is what you see in much of northern Mexico, as well as in much of southern Texas. Those mountains are seldom as crowded as they look right here; they don’t get any taller west of here, and east of here, they disappear entirely. Whole lotta room to put a river, or several rivers. I’m sorry I didn’t get photos of Chihuahua. One town, Jiménez, was an oasis. And the state capital had an attractive geography, with numerous pointy prominences separated by just enough flatness. It’s the combination, scaled just right, that illustrates so well the spaciousness hereabouts, far better than sheer plains do.

Oh, wait. I did attempt one portrait, from my downtown hotel room:

Imagine a city, its interior, I mean, dotted with a couple dozen of those. I don’t think Chihuahua had a single building quite as tall as any of those. Maybe not even the capital was. Little about urban Mexico is reassuring, but this is not a bad look at all.