Baboquivari Geology - Field Trip

Baboquivari Geological Trip Report

by Kent Duryee

One Monday afternoon in March, while carrying out the usual duties of my day to day life, a friend who publishes a small newspaper called, and offered the prospect of getting out in the fresh air, to once again plant boot on trail and nose firmly on rock - cavorting once again on a geology field trip the next Saturday. All he asked in return was this report that you are now reading; these are the calls one only dreams of receiving on Mondays. 

Scheduled just a day before the spring equinox, I was signed up to explore the geology of the Southern Arizona landmark, Baboquivari. The weather reports were promising, and the birds and leaves and warmth were returning to the desert after a record-breaking cold snap. The geology, trail, and rocks won out handily over other pesky responsibilities. No one ever lay on their death bed and rued having shirked their responsibilities for a day of cavorting outdoors. As Richard Bach wrote in his little book Illusions; the adventures of a reluctant messiah, “We are the otters of the universe” - I take my playtime serious.

Baboquivari Peak, in addition to being a well-known, easily identified landmark throughout Southern Arizona, is also the most sacred place, the axis mundi, of the Tohono O’odham people, (Tohono translates as “desert,” while O’odham roughly translates as “people”). The Tohono O’odham’s lands once covered the area from north of Phoenix to southern Sonora in Mexico, and from the San Pedro River on the east, to the Gulf of California on the west. The vastly diminished area where the Tohono O’odham Reservation is now located, on the west flank of the Baboquivari Mountains, is just a small part of their ancient land, but Baboquivari Peak has always been considered to be the religious, cultural, and physical center of their world. Their deity, I'itoi, inhabits a cave on the northwestern flank of Baboquivari, and a large part of Tohono O’odham life revolves around making pilgrimages to the cave to leave offerings and prayers, just as it has for thousands of years. The well-known Man in the Maze symbol is intimately tied to Tohono O’odham religion, known as himdag, or “path,” and represents I’itoi as the man in the maze of life’s journey.

After the work week of drudgery, Saturday dawned. I laced up my dusty hiking boots and quietly slipped out into the last morning of winter, just as the sun was breaking over the Catalina Mountains to the east of my house, on Tucson’s northwest side. A quick stop for water and food for lunch, I then turned the grill of the truck southwest toward Baboquivari. The drive south from Tucson through Altar Valley is gorgeous. The valley is covered in places by lush native grasses playing host to gnarled, bonsai-like mesquite trees. On the west, the valley is rimmed by the Baboquivari Mountains, with Kitt Peak at the northern end, home of the National Observatory, and Baboquivari itself rising bold and vertical above the central portion of the range. Several isolated collections of mountains make up the valley’s eastern boundary: the Sierritas, the Cerro Colorados, and the Las Guijas. Further ranges stretch south toward the border and Mexico beyond, as does Altar Valley itself. The valley seems almost uninhabited for most of its length. Only the occasional small signs and mailboxes along the side of the road indicate ranches with fellow humans sharing the valley’s silent, primeval expanse. 

We were to explore Brown Canyon on the east flank of Baboquivari. The trip was one of several programs and walks sponsored by the Friends of the Buenos Aires National Wildlife Refuge, (BANWR), a volunteer group of citizens dedicated to supporting the National Wildlife Refuge system and BANWR. Brown Canyon is open only to groups under the direction of Friends of BANWR, and the base of operations, so to speak, is the Brown Canyon Environmental Education Center, a beautiful old ranch house that hosts a view down the canyon and out to the east over Altar Valley. A visit to the Center  is worth the a trip all on its own. 

As I continued my southward journey, I paid attention to what wildlife I could see from inside my truck – that morning it was all of the avian variety, well represented by raptors: Harris hawks, Red tail hawks, Kestrels, and the ubiquitous, black-robed, philosophical Turkey vulture. These large birds hinted at other, hidden inhabitants of the valley, just as surely as the signs and mailboxes along the road hinted at the presence of other humans. Where there’s life, there are those who take it, and there are those who clean up afterward. Peaceful, clean, and natural; I sipped my water and contemplated the Turkey vultures as they contemplated me. I checked the gauges on the dash to make sure oil, gas, and coolant were in good supply – no sense in hurrying my no-doubt eventual encounter with those big, brooding, soaring birds. 

Providing the vultures with a moment of exhilaration and hope, while absorbed in these musings, I sailed on by the right turn that would take me to Brown Canyon. I circled back around and found the road leading west off the highway – the big “Brown Canyon” sign facing the other way from which I had come – and was merrily on my way up the dirt road, headed straight for the base of Baboquivari, vultures silently cursing their luck, forever circling in the distance, breathing down my neck.

After several miles I came to a trailhead parking lot and a locked gate. So, I thought, this must be where we would meet. I turned off the truck and gamboled about the place a bit, eyed an informational display with maps and brochures, looked out over the way I’d come, and enjoyed the silence and space. Cicadas whirred away in the grasses, and scrub jays and little brown birds went about their daily ways, paying little attention to me and the cooling engine of my truck, emitting ticks and pings as the stressed metal of motor and exhaust systems contracted volubly back into their normal state. After some time had passed, a man in a pickup truck came by via the direction of the locked gate, looked at me and surmised immediately that I must be a member of the geology group. He kindly gave me directions to where the rest of the group was actually congregating about four or five miles back down the road the way I had come; had I read the material that was sent out to all of the participants, I probably wouldn’t have needed this kind man’s help at all. I was still giving those vultures little moments of hope despite myself.

Back into the truck, back down the canyon road, I came across the 20 or so souls that would make up the group for the rest of the day. The leader of the walk, Richard Conway, was summarizing the surrounding geography and giving a vulture’s eye view of the geology around us. We were at a high point between the valley floor and the base of the Baboquivari Mountains. Some agency, probably the Wildlife Reserve or the Border Patrol, had erected a wireless beacon with the following instructions to those who might not be as fortunate as we were to have been standing there in the desert, voluntarily enjoying the scenery: 

If you need help, push the red button.
Rescue personnel will arrive shortly to help you.
Do not leave this area

The message was translated from English into Spanish, and also the native tongue of the Tohono O’odham nation. Not everyone can laugh at themselves for giving vultures hope for a meal, or even find the concept amusing at all. 

After our orientation we bundled back into our vehicles and wound our way slowly up the dirt road into Brown Canyon. We arrived at the Environmental Education Center, collected ourselves and our gear including lunch, and met at several benches strewn with rocks. We must be in the right place.

Richard had us sit and start looking at the rocks while he discussed basic geologic concepts related to the rock cycle – how rocks are born, change into other rocks, and melt back into the earth’s crust again, only to emerge again in another guise somewhere else on earth. The nature of the rock cycle is that any given type of rock, a chunk of lava for instance, is always in the process of becoming something else. It might be in the process of eroding into sedimentary sandstone at the earth’s surface, or it could be buried deep within the earth and being changed into another rock entirely. Richard calls the names we have chosen to call rocks “boxes.” He does so derisively. He prefers a more holistic view of the entire concept of rocks; something called a “rock continuum” would probably make him happier than placing labels on different rocks like basalt, diorite, rhyolite, granite, limestone, all the while insisting that the rocks conform to our names for them. Labels, names, or “boxes,” don’t account for the dynamic and changing nature of the earth itself, and as such limit our understanding of the earth processes that we witness around us every day. Geology, for all its accuracy in mapping, rock chemistry and geophysics, is at its core a very poetic science. Geology attempts to shed light, not only on our earth, but on the dynamic and changing nature of the universe itself. No easy task without liberal doeses of poetry and imagination.

After our introduction to “Conway’s Rock Continuum,” and a brief overview of the rocks we would encounter on our walk, we were ready to head further up the canyon and put our noses to the outcrops, as geologists refer to the act of getting out in the field. After the primer, we all walked with our eyes down in front, looking at the rocks that passed by under our feet in a way that most of us usually don’t. Every so often we would stop and Richard would describe a certain rock and its relation to the surrounding geology, and the participants would dutifully note these things in their spiral-bound books and nod their heads in eager understanding. It’s wonderful to see people pay attention as never before to their surroundings, and see the most basic of things – rocks and dirt – in new and exciting ways. New discoveries are always exciting, and a trip like this is always an unearthing of discoveries and new insights for people who simply take time to look closely at where they stand.  

It turned out that by walking up-canyon toward Baboquivari, we were actually traveling in Deep Time ourselves, on our way to discovering how the Baboquivari Range came to be formed. But first we needed to stop for lunch. 

A tree-lined, dry wash with towering sycamores in their first green leaves of spring, and lots of rounded boulders and logs made a nice glade to stop at, so we all gratefully shed our packs in the thin shade and dug in to our individual ideas of lunch. I had Italian salami, Swiss cheese, a small boule of French bread – a very Euro-style feast – and very satisfying after a morning walking along in the sunshine nourishing an appetite. Washed down with still-cold water from my pack, I could feel my muscles relaxing and eyelids giving in to gravity, but there was more to be seen and discussed. 

While the rest of us were dropping packs and digging in, Richard had gone on ahead and rounded the next corner in search of something. He brought back a large, rounded rock. I thought that he had searched out that particular rock to use as a place to sit and eat lunch; no one could blame him for that, it was a nice rock.  However, the rock held a telling clue as to the processes that were responsible for the rise of the Baboquivari Mountains, and was instructive about many of the mountain ranges of the Intermountain West, all the way from Mexico to Northern Canada. He set it down in our midst, and sat a short distance away on an unobtrusive log and began the story I’d been waiting for. 

I declared geology as my first major in college precisely because of field trips like this. Sadly I wasn’t up to the math involved in the major, and so, (after many, many geology lab and field courses, and of course field trips), followed history as my field of investigation instead. Geology is nothing if not history, so I now feel equally comfortable studying human history, or studying the almost infinitely deep and vast geologic history of the planet and universe – Deep Time, as it has been called. When applying the Deep Time scale, a million years suddenly turn into the minimum time it takes to get something done. Our lifetimes, and in fact all of human history, flash like sparks and disappear in less than an instant, all but unnoticed while the universe and the earth continually unfold, indifferent to us and our own tiny time scale and imagined, inflated sense of importance.  

Theories vary but generally speaking, in the recent geologic past, 30 – 35 million years ago, tectonic events took place off of what would become the west coast of the North American continent that lead directly to the formation of the Baboquivari Mountains. Some say that it was an oceanic plate that thrust under early North America. Others say that island arcs like Japan and the Aleutians rammed into the continent. Whichever scenario occurred, the result was an upward buckling of the continental crust between the then-west coast, and what are today the Rocky Mountains. When the earth’s crust buckles like this, it has to stretch to accommodate the strain. Just like inflating a balloon, when the earth’s crust stretches, it thins. This thinning makes it easier for magma within the crust to rise, and not only erupt in volcanoes, but also to interact with and change existing continental rocks through heat and pressure. 

Now, just like in a lava lamp, a huge bubble of molten magma neared the earth’s surface. Can you picture the crust bulging above the rising bubble? That is precisely what happened where the Baboquivari Mountains are now. As the magma bubble continued to rise within the crust, surrounding rocks were changed – metamorphosed – into a kind of hot paste, (picture Silly Putty), which allowed other, cooler rocks closer to the earth’s surface, to crack and literally slide over the slippery metamorphing rocks bulging above the intruding magma body. This sliding action can take place over many miles, and it leaves evidence in the form of the very type of rock that Richard brought back from around the corner and plopped in our midst. It was one of the semi-molten rock types that allowed the sliding of rock layers to occur above it; solid evidence of the complicated mechanism that produces something called a metamorphic core complex. Baboquivari Peak is the cooled remnant of the magma bubble that rose within the crust. 

Metamorphic core complexes have been compared to pimples. Aside from the derision involved in the comparison, the analogy is a good one. Seen perhaps through a high speed playback of 10 or 15 million years, the bulging, erupting, cracking, sliding, and cooling process would indeed look much like the formation of a pimple. A sad analogy to be sure, but nonetheless, one that’s easy to grasp.

There are literally hundreds of metamorphic core complexes throughout the Intermountain West from Mexico to northern Canada. The Catalina Mountains north of Tucson are perhaps the most obvious and well-studied of these geologic features. The next time you come into town, notice how the layers of rock above the Foothill communities look like they could still be sliding down the inner sides of the mountain range. That’s exactly what happened.

So, with a new and deeper understanding of how the landscape around us was born, evidence of the event littered around our feet, we finished our lunches and relaxed for a few minutes more in the shade of the greening sycamores, and then it was time to head back out of the canyon, back to the Education Center and our cars, and from there back to our own lives outside of Brown Canyon. We all returned with eyes open a little wider, and minds expanded a little more by walking in Deep Time.

As I neared the pavement, I slowed and looked up into the afternoon sky. There they were. Four Turkey vultures circled high above me, riding invisible air currents, scanning the horizon for miles around – engaged in their own continuum of life and death above the rocks and peaks of Altar Valley. My muscles felt used, I was comfortably tired, and had enjoyed a full day outside in a gorgeous canyon exploring wonderful terrain. I thought about the responsibilities that I had shirked for the day and smirked, not feeling the smallest shred of guilt. My inner otter smiled.

There are many adventures and educational experiences to be had at the
Buenos Aires National Wildlife Refuge and the Friends of BANWR can assist you.

For more information, call 520-405-5665 or email fobanwr@gmail.com.
A great deal of information is available online at
www.friendsofbanwr.squarespace.com