Unit 7 Drain near the confluence of the Rio Grande and the Rio Puerco.

NEAR THE CONFLUENCE OF THE RIO PUERCO AND THE RIO GRANDE – The broad delta where the Rio Puerco meets the Rio Grande in central New Mexico has never been a great place to live, though people try. To the east, across the river, the Ancestral Puebloan Piro built the village Spanish colonizers named “Sevilleta” (“little Seville”) on a Pleistocene gravel bench up out of the flood plain. Because when the Rio Puerco is in flood, it really is in flood.

In their 1984 book Rio Abajo: A Prehistory of a Rio Grande Province, Michael Marshall, Henry Walt, and colleagues chose a naming convention that I like, even though it is confusing as hell. The traditional naming convention for the Rio Grande in Spanish New Mexico is to divide the river and its human communities (as always, the physical geography creates the structure the human communities follow, but it’s the human communities driving the naming) thus:

• Rio Arriba for the landscape north of the great escarpment known as La Bajada.
• Rio Abajo for the landscape south of La Bajada

But both physical and human geography suggest a second division. It is worth quoting their reasoning in full (Marshall and Walt 1984, p. 1):

The term “Rio Abajo,” as it is used in this volume, is of Pre-Revolt vintage and applies specifically to the Pueblo and Hispanic province of the Piro, believed to have extended from the Paraje de Fra Cristóbal on the south to Abeytas or Sabinal on the north (Figure 1.1). In 1776, nearly a century after the demise of Piro-Hispanic civilization in the Socorro region and just before the resettlement, Fray Francisco Antanasio Domínguez divided the Kingdom of New Mexico into two sections: Rio Arriba and Rio Abajo (Adams and Chávez 1956:7). At that time, Rio Abajo was described as the area from Cochiti Pueblo on the north to below Isleta Pueblo (i.e., Sabinal) on the south. Since the emphasis of this study is on the Piro and the Pre-Revolt era, we have employed the archaic usage of the term “Rio Abajo” from the time when Colonial Hispanic settlements extended as far south as Senecú. From a research perspective it is logical to describe the region north of the Piro district and south of La Bajada as “Rio Medio,” although this term is not found in the historic archives.

Historical Topographic Map Collection

Spatting with its much larger sibling, the Puerco at the confluence, with its ephemeral flows but massive sediment load when it does run, has shoved the Rio Grande to the east in a broad bend that snaps nicely into view in the 1952 USGS topo map to the right. Blasting out into the valley floor, the Puerco’s delta has created a broad, gentle high spot, and in flood water backs up the valley to the north. I have seen this.

It is sediment that drives the story my collaborator Bob Berrens and I are trying to understand for the new book project we’re beginning to explore. Managing the sediment in this stretch of the river – from the Puerco and the Rio Salado eight miles downstream, plus umpty named and unnamed arroyos that blast in under the weight of summer rains – is the central challenge for water management in this stretch of the Rio Grande in the 21st century.

We drew our boundaries around the stretch of river from the Puerco down past San Marcial for different reasons than Marshall and Walt. Ours was based on river management, theirs was cultural. In the Marshall-Walt topography, Rio Abajo is the home of a people we’ve come to call the Piro, a name applied by the Spanish to the Ancestral Puebloans who lived along this stretch of the river before Spanish colonizers arrived in the 1500s (Bletzer 2013). But old human settlement patterns and modern river management challenges are built atop the same foundation.

I’m nervous about pushing too hard on the idea that geomorphology drives the structure of human communities on the landscape. Lots of other stuff is involved, but geomorphology lies at the base of the rest of it, our decisions about where to live, to hunt and gather, to build our farms and cities. Why did the Piro build on the east side of the river here? How did they use the river, live with the river? Today, the question about where we build our highways, our railroads, and our levees and ditches, are motivated by the same things. So I put the bike in the car yesterday morning and drove down to La Joya, the state game park on the river’s west side just downstream from the confluence, to try to understand the shape of the landscape.

This has become a central piece of my practice as a writer in the last few years. I’ve always pursued what I have called “journalism by wandering around,” going to a place and just kinda being there, looking around with curiosity, thinking about how and why stuff spatially fits together. The networked nature of water lends itself to this style of thinking, because water moves in paths, and the humans moving with it follow and, increasingly, shape those paths. In the last five years, as my work has become more intimately place based, I’ve done it on my bicycle. I move at the right pace to feel the landscape.

I parked at one of the “La Joya Wildlife Management Area” pullouts near the river and headed north, up the east side service road (the side closest to the river) for the Middle Rio Grande Conservancy District’s Unit 7 Drain, a bizarre water management channel that does what it says on the tin. I need to do a full post on the Unit 7 Drain, it’s super weird. It snakes through the Lomas Pardas Narrows downstream of the Puerco, siphons under the Rio Salado and into the Angostura de San Acacia, winding parallel to railroad tracks on the west and the Rio Grand’s main channel on the east, slicing through a wildlife refuge and hunting park, turning drain water into a fresh source of irrigation supply for Socorro County farmers. It’s one of my favorite spots on the river and is for sure one of the weirdest MRGCD ditches, right up there with the place in the South Valley where the Barr Canal cuts through a junkyard. There is, or was, a much beloved Albuquerque post-punk band named after the Unit 7 Drain. You can’t make up shit that good.

Picking which side of a ditch to ride on is always tricky, because I want the side that’s most rideable, meaning least sandy. But I also want to be on the side closest to my ultimate destination, because often there aren’t any crossings, and wading through a ditch with my bike is impractical. The road yesterday was good, the sand mostly packed down by recent summer rains, which also made it green. The white-crowned sparrows seemed happy with the results, if not annoyed at my presence, doing that thing they do where the clustered in groups around the ditchbank vegetation and dashed out ahead of the bike, as if they were escorting me.

Rio Grande Hunt Club?

I was deterred from reaching my goal – the actual confluence of the Rio Puerco and the Rio Grande – by a gate and a no trespassing sign on the service road. I was pretty sure this was the classic western move of putting up “no trespassing” signs to privatize a public space, but I was having a leisurely morning and didn’t fancy a confrontation with the sort of entitled people with guns who frequent “hunt clubs” and exploit murky areas of law to claim ownership of rivers, so I turned back.

A look at county and MRGCD property maps when I got home supported my hypothesis – the actual private property involved is a third of a mile away, and the service road itself sure looks to me like MRGCD property the whole way – in other words, public property – both sides. But MRGCD access rules are complicated, and a careful post-ride study of the satellite imagery now that I have a better feel for the place suggests several routes to the confluence that should avoid any entanglements with the gray areas of rivers and property law (see Adobe Whitewater decision – the hunt club people do seem to actually own a big piece of the Rio Puerco itself). So I’ll be back.

References:

• Adobe Whitewater v. NM State Game Commission, 519 P. 3d 46, 2022 NMSC 20 – NM: Supreme Court, 2022
• Bletzer, Michael. “The First Province of that Kingdom: Notes on the Colonial History of the Piro Area.” New Mexico Historical Review 88, no. 4 (2013): 4.
• Marshall, Michael P., and Henry J. Walt. Rio Abajo: prehistory and history of a Rio Grande province. Museum of New Mexico Press, 1984.

Albuquerque Journal, June 17, 1951

If you have ever been to modern San Marcial, New Mexico – or what is left of it – the notion of an 86-pound catfish requires some explanation.

The spot where D.C. George hooked his record catfish is today ragged scrubland. But for a brief, shining, extremely odd period of time in the 1940s and ’50s, Lake San Marcial was a big deal.

It was popular with the hook and bullet set, while on occasion also swallowing Atchison, Topeka, & Santa Fe locomotives (so, less popular with the railroad).

It was the subject of dueling litigation. The railroad was mad about the swallowed locomotives, blaming the federal government for causing the lake. The Hunters, owners of the fishing resort, got mad when the federal government decided to drain (or maybe fill?) the lake, so they sued too.

It is a useful example of a common sequence of events when we engineer a river:

1. Change a river with engineering.
2. Something weird happens.
3. People and ecosystems improvise, optimizing around the new state.
4. But the new state causes problems, too.
5. Try to fix these problems.
6. People who had optimized around the new state, or who value the ecosystem’s optimization around the new state, are pissed about the change.

Located 120-ish river miles down the Rio Grande from Albuquerque, the town of San Marcial was a happening place in the early 1900s – major railroad employment center, heart of a what was, in the romantic retellings, a lovely little farming valley with its sibling Tiffany just up river and Val Verde across the narrow desert valley.

As the retellings often point out, it had an opera house. (I’m a writer. I get it. How can you resist an opera house.)

Upstream from a geomorphic bottleneck – the volcanic Black Mesa to the east, a string of sediment-laden arroyos coming in from the west – the San Marcial reach of the Rio Grande has long been a trouble spot for those bent on settling on the valley floor. Flooding was not uncommon. But with the 1916 completion of Elephant Butte Dam to the south, the flooding got worse. Elephant Butte’s full pool elevation is downstream of the bottleneck, but as a reservoir encroaching from downstream slows a river, sediment deposition creeps upstream, often well beyond the reservoir’s actual high water mark.

Whether Elephant Butte’s presence, the sediment deposition, actually caused the flooding that in 1929 ended San Marcial’s opera house days would be the subject of some legal debate in the decades that followed. A federal judge in 1960 ruled that the federal government, builder of Elephant Butte, was not to blame but, as I said, further research needed.

Base Level, Aggradation, and Grade

The modern scientific consensus seems to be that, duh, of course Elephant Butte caused the demise of San Marcial.

Perhaps the most notable example of the aggrading wedge upstream of a reservoir is at the Elephant Butte reservoir, built in 1912 on the Rio Grande about 300 km downstream of Albuquerque, New Mexico (Eakin, 1936). By the 1930s, the Rio Grande had aggraded many kilometers upstream of the head of the lake. Because the sediment load was sand, most of the aggradation was in the channel with the creation of natural levees. Drainage from the distal land on to the floodplain was blocked from entering the stream by the natural levees and thus the floodplain became a wetland and was even ponded in many places. Near the reservoir, the stream level was superposed, or higher than the floodplain. By the 1930s, a local village, San Marcial, began to be flooded and was finally evacuated (Eakin, 1936). It was feared that the wedge of sediment would eventually extend all the way to Albuquerque but that never happened (Mackin, 1948).

– Trimble, Stanley W. “Streams, valleys and floodplains in the sediment cascade.” Sediment cascades: An integrated approach (2010): 307-343.

Sediment Wedge, Ramah, New Mexico.

In their seminal paper Base Level, Aggradation, and Grade, Luna Leopold and William Bull explained how a river slows and drops is sediments as it reaches a controlling base level. The most obvious example is the ocean, which on geomorphological time scales is relatively stable. The result is a wedge of sediment well upstream of the ocean itself. This also happens when we dam a river. The reservoir level acts like a mini-ocean, and the sediments back up well upstream of the of the reservoir level itself as water slows down and spreads out.

Natural constraints do this as well – constraints like the pinch point between the volcanic mesa to the east and arroyos dumping in their load from the west just downstream from the ill-fated community of San Marcial.

A tale of catfish and willow flycatchers

San Marcial Lake

The weird thing for today’s blog post is the lake, which seems to have emerged in the 1940s, perhaps following the floods of 1941 and ’42, which pushed Elephant Butte to its high stand, depositing sediment in this reach and in general causing a geomorphologic mess – not a mess for the river, the river’s just doin’ river stuff, but a mess for the humans who had taken on the obligation of managing the Rio Grande.

Like, trains kept falling into Lake San Marcial, but more importantly for the task of river management, water that humans wanted to hurry on down to Elephant Butte so folks downstream could water their crops was instead spreading out in the “lake” and surrounding swamps. The river no longer flowed here, and New Mexico as a result had fallen hundreds of thousands of acre feet behind in its obligations under the Rio Grande Compact to deliver water to Elephant Butte Reservoir for use in Southern New Mexico, Texas, and Mexico.

Draining the lake and those swamps was as a result a passionate imperative among New Mexicans in the 1950s, as we essentially agreed to federalize the river so the taxpayers of the nation, after helping create the problem by subsidizing Elephant Butte Dam for our benefit, were now asked to again subsidize the fix to the problem created at Elephant Butte’s upstream end.

The Middle Rio Grande Project

The Flood Control Act of 1948 (and a subsequent 1950 iteration) authorized the US Bureau of Reclamation and the Army Corps of Engineers to, among other things, “fix” the San Marcial stretch of the Rio Grande- “river rectification” was the formal terminology of the day. To do that, the Bureau dug what amounts to a second river channel, which today we call the “Low Flow Conveyance Channel,” alongside the river’s old channel. Here’s the explanation from Chris Gorbach’s 1999 history (found in these conference proceedings):

In 1951, President Truman gave Reclamation special authority to start channel construction immediately. Work on the low-flow channel and clearing a floodway for passage of higher flows began in October of that year. Construction on the low-flow channel continued throughout the ’50s. A first phase, the so-called San Marcial Channel, was completed at the end of 1953. Diversions through a heading near the southern end of the Bosque del Apache began in November of that year. Extension of the low-low channel upstream to San Acacia was completed in 1959. When completed, the low-flow channel extended some 70 miles from San Acacia to a point just above the narrows of Elephant Butte Reservoir.

By 1956, the lake where D.C. George hooked that 86-pounder was dried up, turned to grazing land for cattle, and the Hunters were suing the federal government over the loss of their fishing resort. Further research needed on the demise of San Marcial Lake. The news coverage of the day suggests the Bureau of Reclamation diverted silt-laden Rio Grande water into the lake to fill it up. The Hunters called that negligence, the Bureau responded that, no, it was exactly what they intended, and were authorized by Congress to do.

Laguna de Fray Cristóbal

Three quarters of a century after the demise of San Marcial Lake, we’re experiencing a repeat. About ten miles downstream, a large body of water has emerged, apparently of some interest to anglers, certainly of great interest to Southwestern Willow Flycatchers (ecosystems improvise, optimizing around the new state), and also certainly of extraordinary interest to the water managers of 2025 charged with carrying out the obligations we took on as a community when we began engineering the Rio Grande more than a century ago.

Off to the west of the end of the Low Flow Conveyance Channel are 100 acres of open water surrounded by wetlands that are, from a “water in the desert” environmental aesthetic perspective, a delight created by leaks and levee failures in a stretch of the river that doesn’t get a lot of love. The Bureau of Reclamation has even installed gizmos to divert some of the water now flowing down the Low Flow Conveyance Channel into this wetland, beloved by the endangered flycatcher. But in a world in which competing and conflicting values include a desire to move water to farms and cities downstream, in the process meeting the legal requirements of the Rio Grande Compact, the River Mile 60 pond is not universally beloved. Here’s Middle Rio Grande Conservancy District CEO/Chief Engineer Jason Casuga in a letter to the state last summer:

What was originally a failure in infrastructure has now become a managed habitat feature by the federal government. The breach channel eventually makes its way back to the river some 7 miles downstream of RM 60. MRGCD is concerned about the depletions taking place within the breach channel and adjacent floodplain habitat when you consider the area of inundation is likely between 900 to 1,500 acres and has a corresponding evapotranspiration rate of more than 5.5’ per acre annually (based on OpenET).

At a time New Mexico is falling farther and farther behind on its compact obligation to communities in Southern New Mexico and Texas, this is a problem. It is an example of the sometimes competing and conflicting values at play when we take on the enduring obligation of engineering a river.

In a letter last week (July 17, 2025) to the Bureau of Reclamation, New Mexico Office of the State Engineer General Counsel Nat Chakeres gently suggested that diverting water into the wetland was not in keeping with the aforementioned Flood Control Acts of 1948 and ’50, which authorized Reclamation to bail us out of the messes that Reclamation in part created by building Elephant Butte in the first place. Chakeres’ argument is that the acts of Congress setting the whole thing up explicitly prioritized delivery of Compact water.

In summary, the sole authorized purpose of the LFCC is to convey water to Elephant Butte for compliance with the Rio Grande Compact. If water is diverted from the LFCC and consumed for habitat purposes, that is water that could have been delivered but was not.

There’s been some discussion about what we should call the River Mile 60 pond. A number of names have been suggested, but none capture the grace of this much-maligned, often forgotten but, to my eyes, magnificent stretch of the Rio Grande.

Nearby is the old Paraje de Fray Cristóbal, a hardscrabble stopping point on the old Camino Real. I suggest we call it “Laguna de Fray Cristóbal.”