by Craig Childs
Now he was sitting in the shade, eating a rapidly drying piece of bread, staring over the canyon. No one talked. No one looked at the others. It was midafternoon in a region referred to as Tierra Caliente, Hot Land. This is distinguished by name from the low deserts of Sonora, which are simply called Desierto.
Between Nacozari and El Tigre is an increasing intensity of canyons, the map looking like an impossibly tangled fishnet with canyons, cañadas, and cañoncitos twisted across each other. Pieces of the map were left blank, these parts of the land having never been rendered to paper, like the Unknown Territories left by Lewis and Clark. The person with us who was supposed to be doing research was the first to say something while we sat there. Without looking away from the vista beyond the truck, he said “There's no John Wayne-ing through this country,” meaning that we can't just get up and walk across it. We'll have to put the spare on and keep following the road. His voice sounded like a rock falling out of nowhere. Then quiet came again.
The canyon floor could not be seen from this part of the road. Steeper walls bore reddish minerals and stood almost entirely vacant of plant life. I could see, just barely, the tops of cotton-wood trees bulging from the floor. Out of this, two common black-hawks rose in sweeping circles, not seeming to pay attention to each other, but regarding the rising wind of a heat thermal that put them in the circle together. “Common” is not a proper first name for them. Not here, at least. They are, instead, rare, especially here because they frequent marshes, rivers, and mangroves. They are not to be expected in Tierra Caliente.
These birds do not dive like most hawks. They hop and plunge on the ground, jabbing at frogs and fish, swerving around in dense riverside growth the same way owls haunt their forests. On a thermal they looked like any other hawk, though: wings as broad as possible to grab the rising heat, the longest feathers spread like a hand on a globe to allow the heat and wind to thread through at measured intervals. I stood and walked past the truck, past the flat tire, to the edge of the road where I could look over the backs of these birds. Sunlight sank through my hat. My hair turned hot. Still, the canyon floor was out of sight. Water might be down there. I checked the map. The place below was called Los Alisos, The Sycamores. That was all.
With the spare tire installed, we again pressed our shoulders together, scooted in far enough to slam the door. I had the window side in the cramped back seat. Gear pressed against the back of my neck. The truck lurched and popped over a rock, sending our shoulders forward. The bottom of Los Alisos was a jungle. I couldn't see inside. Bare rock walls came down like lava pouring into the ocean, and where they met the bottom, green boils of steam burst upward in the form of cottonwoods, willows, sycamores, and hordes of smaller, herbaceous plants. Where there was enough room on the walls, organ pipe cacti crowded the perimeter of the forest with stately, candlestick arms. Hundreds of cacti, each fifteen or twenty feet tall. Heads of palm trees showed through the cottonwoods. Palm trees, organ pipe cacti, and cottonwoods. What kind of place is this? I hugged my arm out the window.
One of the rarest forests in the world is the desert cottonwood-willow forest, which grows along the few and modest creeks out here. These forests cover less than 2 percent of the American Southwest, making this the most uncommon forest type in North America. The canopy below towered a hundred feet off the ground. Around good desert creeks, mature cottonwoods and willows can reach densities of five per acre, standing above fifteen submature trees of the same species, eighty saplings, and twenty thousand seedlings. The desert typically begins immediately beyond, sometimes in a line you can draw with your finger.
Within these forests are layers and hidden chambers—interfaces between the desert and the forest, and between plant assemblages and various depths of groundwater. Even from the road I could see this: variegated shades of green flowing from open patches to closed patches. The canopy, drawn along a narrow causeway, had the undulating topography of a cloud top. Floods will leave thick piles of sediment in certain areas, making the stretch longer for roots to access groundwater. In other places floods will scour right down to the water table itself, allowing for entirely different types of plants. This turns the forest into a mosaic of colors and brands of shade. The only reason any of this was here would be water, perhaps even water running on the surface—a creek. There were plenty of canyons. We had been driving around them all day. None had forests. They were all made of dry rock and cactus until here.
Palm along a Mexican stream
Each type of plant tells something about the distance to water. Whenever you see a dense, healthy cottonwood-willow grove like this, you can be assured that the water table is within ten feet of the surface. At night, when the trees no longer have access to sunlight for photosynthesis, roots let go and the water table rises slightly. First-year seedlings of cotton-woods and clusters of lush seepwillow will grow only where the water table is within three feet of groundwater. Even if water is not running on the surface, you will know where to find it, by digging at night. Along these creeks, if the water table drops by one foot, about a quarter of the undergrowth will die off. Three feet will kill almost everything but the large trees. Considering that in some places human activity has sent desert water tables down by 650 feet, these riparian forests—forests associated with large water supplies—have not fared well. Many 150-year-old cottonwoods at desert washes stand barren and dead. In Arizona, nearly all of the once perennial desert streams have been robbed by the pumping of groundwater and the diversion of surface water.
From the window of the truck, the forest of Los Alisos looked healthy. Few human developments reached this far. Cattle grazing was scant and no industrial demands drew on this groundwater. What I saw below would be a subset of the cottonwood-willow forest type. It was a cottonwood-willow-palm forest surrounded by organ pipe cacti, a combination of large plants almost too exotic to be seen in one place. The rarest of the rare.
As we came down the switchbacks, I could finally see running water in Los Alisos. It looked like ice tumbling down a chute. I leaned forward to make an announcement. The driver turned, with his chin over the steering wheel, to see me in the mirror. “Listen, when we get to the bottom of this I should go on my own,” I said. Everyone stayed quiet. The driver kept looking back at me. “I'll come back to the road in three days and meet you as you're driving out. I'm just thinking that this stream is where I should be. I've been looking for this.”
Exactly as I finished saying this, an event occurred that would be secretly blamed on me for the remainder of the trip. I would later feel the stare of the man trying to get to El Tigre. Maybe I had wished it. A sharp hiss came out of a back tire. It oscillated as we rolled down on it, sounding like a towel slapping round and round. We got the truck to the bottom of the canyon, where the road crossed this small, clean creek. In the shade of willows we let the tire deflate all the way. We had used our one spare. No more tires.
Hitching out on this road would take some time, days. We posted ourselves in shifts beside our display of flat tires, waiting for the unlikely passing of another vehicle on a rough road that seemed to go to nowhere. Since my shift would not be until tomorrow, I left with another man, walking up the creek, clear water flowing to my shins. We began through a tunnel of young cottonwoods, the stream path dotted with shadows each the size of a cottonwood leaf. Along the west shore was a procession of leafcutter ants, marching their scissored triangles of leaves that looked like sailboats traveling in a wobbling line. Occasionally we found a cottonwood of unusual species—the white cotton-wood, called guerigo or alamo blanco, known in scientific nomenclature as Populus alba. With bark white like that of a birch, it stood out among the light brown trunks of the more common Fremont cottonwoods. The petioles of the guerigo leaves arched more than those of the Fremont and broadleaf cottonwoods, causing the leaves to droop. A house could be built in its shade. An ashen-colored canyon tree frog hid in the guerigo's last, slender roots that gathered at the stream bank.
The other tree of unusual nature is the palm. Its fronds cast a slightly blue shade as the sun came through. The only native, naturally grown palms you would see in the deserts of the United States would be hidden in the few slender canyons with springs in Arizona and California. I do not know what species this was. The shape and color of its leaves were not the same as the fan palms, Washingtonia filifera, I had seen in more familiar country. They were not the anorexic palms you might expect on a white sand beach, swaying over the water and dropping coconuts. These were stout and straight. Still, their stalks were slender compared to the sycamores and especially to the bulky, branch-laden walnut trees and cottonwoods growing all around. Willows brushed against the cylindrical trunks of the palms.
Everything near the creek had flood debris strapped all over it. Parts of trees had become stranded against the canyon walls. Mario, the federal ecologist who joined us in Nacozari, had grown up around here and earlier today told me about floods. His father had worked in the area, carving some of these roads. Once, he and his father were driving in this canyon, where a road that no longer exists crossed the floor. As they rattled up the creek they both saw the front wave of a flood coming down. It was a summer flood, one of those big thunderstorm-driven waves that shows without warning, ravaging the canyon for an hour or two before dying completely away. I asked how big. “Bigger than the truck,” he said. His father popped the gears into reverse and spun the truck backward. A hundred meters in reverse, Mario said, as fast as the truck could go, jolting over rocks, throwing objects out of the bed. At a clearing his father stabbed the gears forward and lurched out of the creek bed, barely clipping the edge of the flood.
Flood history is written everywhere on creeks like this. Pieces of debris are scattered. Trees are left bent over or snapped in half. The desert is an invitation for floods. With sparse vegetation, shallow soils, exposed bedrock, intense localized rainstorms, and high relief to the land, water funnels quickly in this kind of place. Not long ago at all, a vehicle became stalled in one of these Sonoran Desert floods along an Arizona wash. A minivan full of Boy Scouts made it across the first signs of the flood, but entering just behind, a Ford Explorer stalled. It was an early spring storm, a classic slow rain that sent every wash in that part of the desert into flood. A tow truck was called in. It pulled up to the north bank and sent out a tow strap, but the strap broke. Water quickly rose around the vehicle, and the four Scouts and two adults climbed to the roof. By the time sheriff's deputies arrived, water was coursing through the windows, rising quickly. After two hours of rescuers trying to get a rope out and tossing life jackets that were swept downstream, the sport utility vehicle finally gave way. Weighing about four thousand pounds, it rolled into the flood. Rescuers managed to snare three of the people before they were swept away. The remaining three, two boys and a father, perished.
Tree rings record the passage of floods, not only by the scars of violent impact but by the ages of trees themselves. Cores taken from cottonwoods and willows on the Hassayampa River, in Arizona's Basin and Range Province, tell of cycles. About once every ten years a large number of trees establishes itself, an event that coincides with unusually large floods. The floods act as nurseries. The shedding of seeds from cottonwoods and willows matches late winter and spring floods as if the event were staged, the seeds seeking the sanctuary of large water releases. But trees cannot drop seeds on demand, whenever a storm of a certain size happens to enter the region. The event has been phylogenetically planned for, the timing of desert floods printed into the genetic strands of the plant.
Summer floods are too sudden and too furious, and vanish too quickly to adequately recharge the groundwater. Winter floods are slow and large, steadily raking over periods of days or even weeks. On a February day, a month before the death of the Scouts, I had walked to an Arizona creek bed that I usually found completely dry. Storms had been around for two weeks, and I arrived at a canyon floor that was now running thirty feet wide, probably fifteen feet deep. An actual river through the desert. Sediment had already been purged and the flood now ran clear. A clean flow is something you will never see in the sudden madness of summer floods. In the summer you will see only rocks, boulders, broken trees, and a thick slurry of fast mud. A fleet of canoes could be run down the smooth water of this winter river, a river that would probably be parched for the rest of the year. The seeds of cotton-woods were just preparing themselves to fly, stretching their cases on the demand of the season. Willows were only shortly behind, planning to catch the final stages of the flood, allowing them to grow closer to the center than the cottonwoods.
Floods are the key to keeping these places alive. Most desert riparian forests do not have perennial streams. They rely on groundwater, which is recharged mostly by floods. So everything living down here has got to be able to survive cataclysm because cataclysm brings life. Physical shapes in the channel are dramatically altered by floods every few years, opening and closing niches, turning the forest into ragtag scraps with different plant communities occupying different patches of fabric. The patches are constantly torn out and moved elsewhere, keeping the forest fresh and mobile.
Even the chemistry of floodwater itself is medicine. Desert streams are notorious for running nutrient-poor; then floods come like compost heaps, thick with nutrients, not only recharging the surrounding soils but also banking away new groundwater that flows beneath the creeks. These subterranean creeks of floodwater sometimes rise to the surface through gravel skylights in the bed, giving a kick of nourishment to the water up top. Wherever these zones of upwelling water appear, even months after the last flash flood, they may carry nitrogen levels 217 percent higher than those in the surface creek, and a feeding frenzy of life gathers at the hole.
This floodwater reserve itself, slowly moving beneath the creek, is one of the biologically safest, most stable regions of a desert stream. It acts as an invertebrate and plant refuge when the surface stream floods or dries—organisms will suddenly start drilling their way down as stress hits the stream surface—and each level of depth in this underworld of stored floodwater shows an entirely new arrangement of organisms, as if the place were tiered underground barracks. Inside this zone is also a store of organisms able to quickly rise to the surface and recolonize the smaller niches left vacant from a flood. It acts as a battery of reserved life and sustenance for the entire stream ecosystem. This is the same nutrient-rich water that came down in violence, probably crushing and drowning nearly every creature along the creek at the time.
With a diet of catastrophic flood, desert streams are themselves in a constant state of flux. A flood erased most of the riparian forest of Date Creek in western Arizona, a place where water flows on the surface in only a few locations. The flood came from Hurricane Nora, which downgraded to a tropical storm as it left Mexico, putting most of its punch into these desert mountains west of the town of Prescott. Arriving a month and a half after the flood, I spoke with a local rancher, Phil Knight, who had been doing conservation work on the creek for twenty-nine years. He ran six hundred head of cattle here, moving them in and out of pasture every month, or every four days, depending on the quality of the range, never letting them near the creek during the summer. For his careful treatment of the land, for allowing a bountiful forest to return to Date Creek, he had received the Conservationist of the Year award from the Arizona Game and Fish Department. He spoke as if his memory was a habitat map, describing by location a zone-tailed hawk nest, certain types of reeds, and places where lush grasses once grew so thick that they laced over the creek. “Boy, it hit this area just harder than hell,” he said. “We've had some enormous floods that haven't done anything. This one took it all. I had thousands of new trees per mile out there. Thousands of them are gone now.”
When I walked up the creek, it looked as if a battle had taken place. Where ash and willow trees had once been thick, and the bed had been made of sand and knotgrass, naked bedrock was now quarried waist-deep. Granite boulders four fe
et wide, probably twenty or thirty tons each, had stacked on top of each other, their nearest source being a mile upstream. I found one boulder the size of a file cabinet clutched in the arms of a tree. Tops of ash trees protruded from new dunes of creek sand fifteen feet deep. I walked into the open desert, and even twenty yards from the wash, mesquite trees had been pushed to the ground. If I had known a flood was coming at the time, even the flood of a century, I would have felt safe standing here. A wall of water and sand would have taken me under. Ropes of debris now wrapped the saguaros.
Phil Knight, sitting in the living room of a house 112 years old, tucked his thumbs into his belt loops and looked toward the ceiling. “This was my little beauty spot,” he said. “Now it's gone.” He did not cry over this. He had seen enough of how the desert operates.
At Los Alisos I picked through flood debris. The last big flood here may have been several years ago. Snags of roots and flood-driven branches hung twenty feet up in the arms of a sycamore. These were maybe from a decade or two ago. A grove of palms had once grown at the outside of a curve in the creek. Now all that was left were short husks of trunks. The palms had been toppled and I could see that they had originally grown at the calm inside of the creek's curve. Whatever flood had last come through rearranged the creek's architecture enough to reverse the water's path through here.
