In the summer of 1921, the U.S. Geological Survey (USGS) set out to complete the first topographic surveys of Cataract and Glen Canyons on the Colorado River and the nearby canyons of the San Juan River. Three parties were sent into the field, each with ​​a topographic engineer, a recorder, rodmen, boatmen, a cook, and a geologist. One party, under the direction of K.W. Trimble, began on the San Juan River near Bluff, Utah, mapping through its confluence with the Colorado. There, they met up with a second party led by W.R. Chenoweth. Chenoweth’s team launched on the Green River, floating to its junction with the Colorado and down through Cataract Canyon to the mouth of the San Juan. Together, the two groups continued toward the Fowler party, which had begun at Lees Ferry, Arizona and was working upstream through Glen Canyon. 

In late April, I joined a trip on the San Juan River that included boat operators and trip logistic extraordinaires from the Returning Rapids Project (RRP); hydrologists, geomorphologists, and geologists from the University of Utah and the Grand Canyon Research and Monitoring Center (GCMRC) of USGS Flagstaff; a documentary filmmaker; and a longtime supporter of Glen Canyon Institute.

Since Trimble’s initial effort almost 104 years ago, this would be the first major survey to map the profile and gradient of the lowest sections on the San Juan River.

In a 1987 guidebook, William L. Chenoweth describes the 1921 surveys, writing that “when the mapping was completed in late October, it gave for the first time an accurate description of the alignment and gradient of the rivers and the topography of their canyons.” The need to map and survey these canyons related to proposed hydropower and water storage projects along the river. Specifically, a proposal to build a large dam on the Colorado River at Lees Ferry required detailed topographic surveys to determine the capacity of the reservoir to come. Lake Powell would go on to become the second largest man-made lake in the country.

The “work” done by rivers upon their surroundings can be distilled into three fundamental processes: erosion, transportation, and deposition, the combination of which carves and shapes the landscapes through which they flow. In this regard, the San Juan is a workhorse of a river. Extremely sediment-laden, the river carries water across a basin underlaid by highly erodible sandstone, siltstone, and shale, its low but consistent gradient eroding this material and transporting it toward the confluence with the Colorado River. 

For decades, however, the waters of Lake Powell stalled behind Glen Canyon Dam have stopped the San Juan’s flow well before that confluence. At full pool, the fingers of Lake Powell stretched 60 miles up the San Juan River, in addition to inundating 24 miles of the Escalante, 186 miles of the Colorado, and countless tributary side canyons in between. When these rivers hit stagnant reservoir water and no longer have the energy to carry their load, sediment drops out of the stream, filling in the river corridor and adjacent bays.

The resultant sediment deposits are almost inconceivably massive. Mike DeHoff, Principal Investigator of RRP, describes them as “the byproduct of mining the Colorado River for its water.” Now, as the reservoir recedes, the river reclaims those miles. The San Juan River does work upon the deposited sediment, cutting down and moving laterally, carving new channels through crumbly silts and stubborn muds. But how quickly is this change occurring? Where are reservoir sediments accumulating, and at what speed are they being evacuated by high-energy flows? How will these processes continue given projected climatic shifts?

While Trimble’s trip was undertaken to map the area’s capacity for proposed reservoir storage, ours is to document how the impacts of that reservoir—and its retreat—have fundamentally altered the river’s sedimentation and hydrologic processes. A group of curiosity-driven researchers, river enthusiasts, and friends, each of us hopes that with a better understanding of the San Juan’s dynamic system, we can shape management policies that fully reflect the complexity of the landscape’s physical and ecological transformation.

Despite the obvious differences between our trip and the Trimble expedition, we both measured stream profile, surveying water surface elevation along the river to build an accurate map. Trimble’s team would have started at a known reference point and measured the distance and elevation change to their next point using an optical level and a stadia rod, a vertical pole with measurement markings. From there, simple trigonometry was required to map the stream profile. (SOHCAHTOA, anyone?)

To take the same measurements, our trip used modern, survey-grade Global Navigation Satellite System (GNSS) receivers to automatically collect position and elevation data. GNSS is a constellation of satellites used for navigation, positioning, and timing that includes the American GPS system alongside similar systems operated by other countries around the world. GNSS receivers were used throughout the trip to produce extremely precise answers to seemingly simple questions, including: “Where are we?” and “How sure are we that we are where we are?” “After post-processing the data collected from the receivers,” explains GCMRC’s Matt Kaplinski, “the error on every point will be reduced to 10 centimeters, about the size of a softball.” He mimes the small, round shape, his wide-brimmed, cloth-covered pith helmet definitively adding to the trip’s expedition mentality.

Hugh Miser, the geologist on Trimble’s survey team, recounts how their party “descended the canyon by using two 16-foot flat-bottomed rowboats, which were built in Los Angeles, Calif., shipped to Green River, Utah, and hauled 170 miles with a quad truck to a point on the river 4 miles below Bluff, Utah. The boats were launched and the canyon voyage began July 18, 1921, and the mouth of the river was reached October 3.”

Aided by the advent of satellites and GNSS receivers, as well as the impeccable planning of Returning Rapids’ Meg Flynn and Mike DeHoff, Trimble’s 2 ½ month survey took us only seven days. We launched from Mexican Hat, 27 river miles downstream from Bluff, converging there from Flagstaff, NM; Moab, Salt Lake City, and Boulder, UT; and Grass Valley, CA. We loaded our gear into five 18-foot aluminum skiffs, the ideal boat for a trip that requires nimble maneuvering through cobbly rapids, portaging a waterfall, inevitably getting stuck on shallow sandbars, and motoring across the eerily clear waters of Lake Powell. Each boat is named after a historical woman of this region: the Bessie, the Jotter, the Doris, and the Dudy—a small nod to those who studied, documented, explored, and loved this place before us.

The night before we launch, some members of the group reconnect while others meet for the first time. We are immediately united by a palpable excitement; we’re going to be conducting science on the river, contributing to a greater body of knowledge. To say that the river has changed since Trimble’s last survey would be—well—a massive understatement.

Boating in a skiff changes the way I see the river. Unlike the classic self-bailing rubber rafts I am used to, these boats won’t slurp over shallow shelves that hide under the surface of murky, sediment-laden water. As a result, barely noticeable riffles become consequential—hitting rocks is a) loud, b) jarring, c) an inconvenient way to get stuck, and d) could punch a hole in these very sinkable boats.

It keeps us attentive. I spy a beaver before it slinks under the water and disappears. Canada goslings try to climb a small bank and, unable to keep up with their parents, tumble head-over-heels back into the water. A big-horn sheep munches vegetation along the shore. As I look closer, more pop out from their camouflaged surroundings. At night, the distinctive calls of Woodhouse Toads roar across the stillness, a screaming chorus reminding me of the breadth of life that surrounds us.

We pass Mendenhall Loop and the San Juan’s famous Goosenecks, winding back and forth through the even grey layers of the Honaker Trail Formation. Here, the river flows sinuously for six miles while advancing only one and a half miles west. Without fanfare—or even my knowledge—we slip into Glen Canyon National Recreation Area.

Soon after, before we reach areas that were ever directly touched by the reservoir, we begin to see its effects. At full pool, Lake Powell inundated the river to Grand Gulch. Sediment deposition there slows the river, causing a backwater effect and a ripple of upstream aggradation: from there, sediment deposition extends around four miles up to Slickhorn Canyon. Relative to the Colorado River, the San Juan carries a higher concentration of sediment down a shallower gradient. This combination results in a backwater effect that stretches over a longer upstream distance relative to the same phenomenon seen on the Colorado.

Even if I weren’t surrounded by the most qualified group of scientists to explain these processes, I could have told you that something shifted in the character of the river that day. The cobble bars disappeared and were replaced by a wall-to-wall distribution of sand. Isabel Adler, a boat operator for RRP, paddled a packraft. Sitting closer to the water, she described to me how the sound of the river changed, how its energy dissipated beneath her paddle blades. At Slickhorn Canyon, Trimble’s party would have navigated a Class II rapid. Now, the river sits 20 to 40 feet higher, flowing on top of excess deposited sediment that it is unable to transport. 

In this stretch of the river, we no longer have to worry about hitting rocks. Instead, we look for hints of sandbars that occasionally ground the skiffs, forcing us to get out, lighten the boats, and walk it across to deeper channels. Slight differences in the water distinguish between the green-tinged thalweg and the shallow sandbars that shimmer with light reflecting off red canyon walls. We prod and weave, dragging when we inevitably don’t get the navigation quite right.

At Clay Hills Crossing, the San Juan breaks away from the confined Cedar Mesa Sandstone and emerges into a wide floodplain. The channel has space to move here, and throughout the river’s long history, it has likely migrated back and forth across this portion of the landscape. The standard guidebooks for the San Juan end here. A sign makes clear why: “DANGEROUS Waterfall Ahead,” it reads, “DO NOT Proceed. Take All Craft Out Here.” We proceed enthusiastically; the waterfall exemplifies why we are here.

When the San Juan River first met this wide expanse of reservoir sediment, it followed a different path than its pre-reservoir channel. The new channel cuts right, abutting the bedrock outcroppings of Organ Rock shale to the west. Here, instead of further incising into the reservoir sediment, it flows over durable bedrock, forming rocky, ledgy rapids: Breakthrough, Bears Ears, Ledge Drop, and finally, the big one—Fatt Falls, where the San Juan River flows over a 25 foot cliff of exposed bedrock. Change in this landscape occurs quickly, geologically speaking. The first waterfall, Paiute Falls, emerged in 1991. It was originally 26 feet tall but has since silted into a twelve-inch, ledge-like riffle.

Fatt Falls emerged in 2003. When we arrive, speculation quickly ensues: has it gotten bigger since the last time we were here? Is the crack in the middle widening? The scientists get to work gathering the data that will ultimately allow us to answer these questions: mapping the elevation profile of the drop, measuring a cross-section of the falls, and using lidar to build an image of the entire area.

Trash bobs in the pool below the falls: oil containers, two basketballs, styrofoam, a camp chair, plastic bottles. Two golden eagles soar high above us. Snowy egrets skim along the water; this corridor of riparian life provides space for a brief reprieve on their long migration northward. 

Later, we float by the exposed tube of a mostly buried raft. A life jacket sits atop the beach, clipped to something deep below the ground. This gear was swept downstream during the San Juan’s high flow event last June when the river rose rapidly after monsoonal rains, spiking overnight to over 20,000 cubic feet per second. No one was hurt, but seven boats were lost. The now-encased gear serves as a clear reminder of the sediment volumes mobilized in the event. Near Zahns Bay, the high flows pushed against the channel’s outside bank until it gave way to a new, more efficient route. Dynamic, transformative, powerful—this river continues its work.

Mike points along the banks, naming three different species of native willows: Gooddings, Coyote, Seep. Cottonwoods branch high above us, all new growth since the retreat of Lake Powell. 15 years ago, we would have been underwater; now, the river nourishes a flourishing ecosystem.

The current flows on, approaching the Great Bend. The rock formations around us take on the characteristic features of the Glen Canyon Group: the sheer wall of Wyngate interrupted by Cayenta layers, the canyon topped by the domed cliffs of Navajo sandstone. These next miles are the closest that we will come to running a river through Glen Canyon—“For now,” corrects Davide Ippollito, an RRP boat operator and river guide. 

In 1924, Hugh Miser published a report describing this section: “Its picturesqueness is most impressive and equals or surpasses the beauty of the canyon in which the famous Rainbow Natural Bridge is located. Its sandstone walls, with their buff, brown, and red colors, are as smooth as the gray granite walls of the Yosemite, and they terminate upward in gigantic rock domes which tower higher than the Washington Monument. Yet they are dented with several alcoves—some with rounded walls like the upper interior walls of a huge hollow sphere and some with straight back walls and arched roofs. To their walls there cling sparse ferns and lichens, which are fed by seeps. Rivulets leap from the rim of the canyon and join the water from springs to form a small, clear stream which runs on the rough, rocky canyon floor.”

As we float around the Great Bend, I take comfort in recognizing these features, in knowing that beauty has endured, persisted, and, all on its own, been restored.

The river-to-reservoir delta transition is always jarring. The channel constricts and we are surrounded by a moonscape of lifeless mud. Stashes of sticks pile up, marking last year’s high reservoir mark. We are pushed into the strangest riffle I have ever seen, forced to navigate the boats through a stretch of drowned, dead willow branches. The wind coats my eyelids with a fine dust. I’m reminded of this when I reapply sunscreen and find myself grinding a layer of silt into my face. I dip my toes into the river—they immediately disappear, the water almost viscous with sediment. 

At the very end, the channel braids as it meets a wide bay of water. Officially in the reservoir, we shuffle gear around, distributing weight so that each boat can effectively get on plane with its motor. I watch the wake behind us take on a seafoam green-brown tinge. Ahead of us, a subtle line bisects the water, beyond which the reservoir shifts another shade greener. And then again. It’s more gradual from there, the water turning ever more clear, white curling caps of the motor’s wake contrasting sharply from the dark, watery expanse around us.

Isabel tracks our current location in comparison to a historic map. “We’re 170 feet above the river right now,” she tells me. 170 feet above where Trimble and his team set up their stadia rod to determine the elevation drop of the river from their last known point.

At the confluence with the Colorado, a buoy sits in the middle of the channel. It reads, “San Juan River,” a redundant marker to those whose sandals are still encrusted with the river’s sand but a necessary reminder, perhaps, to others.

I try to imagine how the view would have looked to the Trimble party—or, for that matter, to those who lived by these rivers and built intimate knowledge of them for hundreds of years before the first official survey took place. For many Indigenous peoples, the confluence on the San Juan and the Colorado is the convergence of male and female life forces. Lake Powell makes this sacred site inaccessible to offerings and ceremonies.

I force my perspective lower. I imagine the water draining out beside me, try to picture looking up at a particular band of rock currently at my eye level. I use the details that I’ve already witnessed from the restoration zone to fill in the gaps—precipitous canyon walls meet the water’s edge beside willow-covered banks, natural bridges perch atop smooth, unscalable cliffs, arched alcoves pocket varnished walls that drip with hanging gardens. Past descriptions and the presently emerging landscapes of Glen Canyon inform this possible future, although that course is one that we have yet to chart.

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Works Cited

• Chenoweth, William L. “The Great Canyon Survey of 1921.” In Geology of Cataract Canyon and Vicinity: A Field Symposium-Guidebook of the Four Corners Geological Society, 29. Tenth Field Conference, 1987. https://archives.datapages.com/data/fcgs/data/018/018001/29_four-corners180029.htm.
• Allen, Robert N., Kelly Trimble, chief of party, USGS survey of the San Juan River in 1921. Taken in Glen Canyon., 1921, The Otis Marston Colorado River Collection, https://hdl.huntington.org/digital/collection/p16003coll5/id/32090/.
• Thompson, Kendall. “Charactertistics of Suspended Sediment in the San Juan River near Bluff, Utah.” USGS, 1982. https://pubs.usgs.gov/wri/1982/4104/report.pdf.
• Miser, Hugh Dinsmore. “The San Juan Canyon, Southeastern Utah: A Geographic and Hydrographic Reconnaissance.” USGS, 1924. https://www.usgs.gov/publications/san-juan-canyon-southeastern-utah-a-geographic-and-hydrographic-reconnaissance.
• Allen, Robert N., Mud Flood. Sand Waves breaking. Looking downstream, 1921,
  J. Willard Marriott Digital Library, https://collections.lib.utah.edu/details?id=2348635.
• Miser, H.D., Photograph album of the United States Geological Survey (USGS) San Juan River Expedition of 1921, 1921, Utah Historical Society, https://collections.lib.utah.edu/details?id=2455155&facet_setname_s=%22dha_pour%22&facet_subject_t=%22Church+of+Jesus+Christ+of+Latter-day+Saints%22&rows=200&sort=modified_tdt+asc.
• Allen, Robert N., Looking down Canyon from near top of Honaker Trail, 1921, J. Willard Marriott Digital Library, https://collections.lib.utah.edu/details?id=2348612.
• Whitis, Duwain, and Tom Martin. Guide to the San Juan River Montezuma Creek to Clay Hills Crossing, Utah. 4th Edition. RiverMaps, 2021.
• Loer, Reed. “8/27/2021 vs. 9/18/1952 San Juan Channel and Wetted Area.” Fort Lewis College, 2021.
• Stevenson, Gene, and Don Baars. “From the Archive: Hot Water(Fall).” Canyon Echo, 2022. Revised from an earlier version in The Confluence, vol. 1, Winter, 1994. https://canyonechojournal.com/2022/02/09/from-the-archive-hot-waterfall/.
• Allen, Robert N., Thirteen feet rapids 2.5 miles below Wilson Canyon “Cha Canyon.” (?) AFTER PORTAGE. October 2, 1921, 1921, J. Willard Marriott Digital Library, https://collections.lib.utah.edu/details?id=2348626&q=thirteen+feet+rapid.