The Continental Divide of the Americas stretches from Alaska to Chile, forming the longest hydrological divide on Earth. This Great Divide represents a tip-off point for some incredible journeys: Rain and snow that fall on the east side of the Continental Divide make their way into streams, rivers, and, eventually, the Atlantic and Arctic Oceans. Precipitation that falls on the west side of the divide finds its way to the Pacific.
But while water gets to run downhill on its journey from the mountains to the sea, the intrepid “thru-hikers” who travel along the relentlessly mountainous spine of the Continental Divide National Scenic Trail in the United States have to contend with more than 280,000 meters of elevation gained and lost as they traverse a 4,873-kilometer-long footpath between Mexico and Canada. To put that feat into perspective, the elevation gain is equivalent to climbing Mount Everest from base camp to summit 80 times.
Neither the Continental Divide nor the Continental Divide Trail (CDT) have been around for as long as one might think; both are relatively young and evolving. Climate change is already affecting both the hydrosphere and the hikers; as annual snowpack dwindles, temperatures rise, and wildfires run rampant. Over geologic timescales, the Americas are headed for the tropics as part of Pangaea Proxima, but it’s unlikely that any thru-hikers will be around to traverse Earth’s next supercontinent.
The Making of a Divided North America
Over the past 2 billion years, the planet’s landmasses have cycled through a series of supercontinents every 300 million or so years in a process called the Wegenerian or supercontinent cycle. However, explained Chris Scotese, a paleogeographer at the Field Museum of Natural History in Chicago and founder of the PALEOMAP Project, “the term cycle is a bit of a misnomer because it’s not a cycle in the sense that there’s a fixed time period.…It’s more an episodic function of operating on a spherical planet. You can’t just open an ocean basin forever. Eventually, things will begin colliding.”
The most recent supercontinent, Pangaea, existed between 335 million and 175 million years ago. Around 200 million years ago, the Atlantic Ocean began opening along a spreading ridge, initiating Pangaea’s breakup—but the divide established on the new continent wasn’t the continental divide we know today. “Before 80 million years ago, the North American Continental Divide was in Nevada, in a highlands we call the Nevadaplano,” said Karl Karlstrom, a geologist at the University of New Mexico in Albuquerque.
Then, between 80 million and 50 million years ago, the Rocky Mountains were uplifted by the Laramide orogeny, creating two major divides, one in Nevada and another in the Rockies. “The process of transferring the Continental Divide from Nevada to the Rockies took place over a long period of time of linking together major and minor divides,” Karlstrom said. “The Continental Divide is the big kahuna, but there are lots of local divides all over the West.”
The Continental Divide is the source of many of the great river systems of the West and Midwest, including the Nelson, Columbia, Mississippi, Colorado, and Rio Grande. On the northeastern side of the divide, the modern Missouri and Mississippi river courses predate the uplift of the Rockies. “All of the [Great Plains] rivers are likely to have greater ancestry in the sense that they generally follow pathways to the Gulf of Mexico that were established early on, before the Rocky Mountain divide got pushed up,” Karlstrom said.
In other places along the divide, the process of forming watersheds and linking those drainages to river systems that reached the sea took millions of years. In the Pacific Northwest, the Columbia River basin was reconfigured many times over the past 17 million years by volcanic eruptions and a series of megafloods at the end of the last ice age. On the central western side, precipitation draining off the Continental Divide pooled into a dead-end endorheic basin for millions of years; a modern equivalent is found in the Great Basin in southern Wyoming, where the Continental Divide splits in two around an internally drained basin notorious for being a hot, dry section of the CDT.
It wasn’t until more recently that the major river drainages of the Colorado and Rio Grande finally found routes to the Pacific and Atlantic, respectively, Karlstrom said. On the southwestern side of the divide, the continued uplift of the Rocky Mountains over the past 10 million years helped carve the Colorado River basin, establishing a relatively young “hydrologic superhighway for Rocky Mountain snowmelt water to reach the Gulf of California,” Karlstrom said. On the southeastern side of the Rockies, the Rio Grande reached the Gulf of Mexico only around 800,000 years ago.
The Crown of the Continent
Today the CDT crowns the Rockies, a chain of mountains laced with snow in winter (in some places more than 12 meters deep) and lashed by thunderstorms in summer. Precipitation that falls in the watersheds draining either side of the divide will run over the surface into streams, infiltrate the groundwater system, or cycle into the atmosphere via evapotranspiration. Depending on the route it takes, a drop of water may take weeks or centuries to complete its journey from the Rockies into the Atlantic, Pacific, or Arctic Ocean.
The CDT follows the Great Divide as closely as possible from Mexico to Canada. Along the way, the remote and rugged backpacking route polishes one jewel after another, including the high mesa deserts and aspen forests of New Mexico, the jagged peaks and “fourteeners” of the Colorado Rockies, the gleaming (if dwindling) glaciers of Wyoming’s Wind River Range, the gushing geyser basins of Yellowstone National Park, and a grizzly grand finale in Glacier National Park in Montana. Insatiable hikers who pack their 1-ounce passport (every once counts!) can continue north on the Great Divide Trail, which follows the Canadian portion of the Continental Divide another 1,130 kilometers north to Kakwa Provincial Park in British Columbia.
Thru-hikers who plan to complete the entire CDT in one season usually start in New Mexico in April and aim to finish at the Canadian border before October. A smaller number of “Southbounders” start in Glacier in June with the goal of finishing at the Mexican border by November. Each year, fewer than 200 people complete the entire CDT, compared with the thousands of people who thru-hike North America’s other two long-distance hiking routes, the Appalachian Trail (AT) and the Pacific Crest Trail (PCT), each season. To date, around 500 people have completed the North American Triple Crown of Hiking by finishing the AT, CDT, and PCT.
Of the trails in the Triple Crown, the CDT is considered the most challenging because of its remote and relentlessly mountainous route. Also, unlike the AT and the PCT, which are decades older and have well-established and generally well marked paths, the route of the CDT, first thru-hiked in 1995, is only about 70% complete. The remainder is cobbled together by an often confusing maze of forest roads. Navigational skills are essential; picking the wrong route can lengthen a thru-hike by weeks.
A Tale of Many Rivers
The Continental Divide itself is not a fixed feature and has as much to do with rivers as with mountain ranges. “The present divide is rapidly evolving, on both human and geologic timescales,” said Karlstrom. “It’s very dynamic, as rivers respond very quickly to any changes in topography.”
For example, in southern Colorado’s San Juan Mountains, both the Continental Divide and the CDT make big swings around the headwaters of the San Juan and Rio Grande river basins, which flow west to the Colorado River and east to the Gulf of Mexico, respectively. “These two rivers are battling for dominance over the divide,” Karlstrom said. “The San Juan is eating its way to the east, pushing the divide to the east. And the Rio Grande is eating its way west, pushing the divide to the west.”
Hotter and drier conditions are fueling bigger forest fires all over the West, and in some years, hikers have to detour around fires burning along the CDT. In the past 3 decades, more than 600 kilometers of the trail have been directly affected by fire. In 2021, the Trail Creek Fire closed a large section of the CDT where it runs along the border of Idaho and Montana, forcing purists who wanted to maintain their continuous footpath between Mexico and Canada to make a 160-kilometer highway walk around the fire or detour on trails to the east, several hundred kilometers off the divide.
Grief and Grizzlies on the CDT
There are many ways to hike a long-distance trail. Thru-hikers aim to hike the entire trail in one season, usually spanning 5–6 months, whereas section hikers may take a lifetime to check off all the sections. Sections are broken down by resupply points, where the trail passes near a road or a town in which hikers can buy food for the next few days or pick up a package at a post office. Most hikers will resupply every 3–6 days, though some remote sections require longer food carries between towns.
Last spring, in the same week I sold my house, my 13-year-old dog, Dio, died. It was the end of an era and several chapters of my life all at once, and the best way I could think of to move forward was by hitting the trail.
Over 7 days, I hiked 160 kilometers on the Continental Divide Trail in northern New Mexico, crossing the Jemez Mountains to Ghost Ranch, on the longest solo backpacking trip of my life. Originally, I planned to hike around 112 kilometers, about 16 kilometers a day, but I discovered I hike much faster when I’m alone, and when I reached the road crossing where I intended to hitchhike back to my RV 2 days early, I kept going another 48 kilometers north to the next paved road, where I thumbed three lovely rides back to my rig.
My hike helped me process my grief and also functioned as a shakedown: I was scheming to join my friend “Montana” (her trail name), who was thru-hiking the CDT from Mexico to Canada, and I wanted to make sure I had all my gear dialed, with no extra weight, and my trail legs ready before I joined her on her quest. Montana hiked the Appalachian Trail in 2019, to honor her son, who passed away in 2015. “The only place I feel happy and healthy is on trail,” she said. “Every day I move through my grief cycle. Being on trail reminds me to just keep moving.”
Jumping on trail with a thru-hiker is no small feat, either physically or logistically. Montana was hiking more than 30 kilometers a day, rarely had cell service, and could only guess when she might cross a road where I could join her. But the stars aligned, and I joined her for five different sections in New Mexico, Colorado, Wyoming, and Montana, including bucket list stretches in Yellowstone and Glacier National Parks. When I wasn’t hiking, I was being a trail angel, helping hikers with rides, resupplies, and logistics.
By the time I accompanied Montana on her final 100 kilometers through Glacier in October, I was as fit as I’d ever been, able to cover 40 kilometers in a day over any terrain. And I felt as capable and centered as I’d ever been, which may have helped me pass the ultimate wilderness test: peacefully meeting six Glacier grizzly bears on foot, deep in their home territory, without so much as a warning huff from the bears.
Montana and I both carried bear spray, which can shoot a potent cloud of pepper spray up to 10 meters. The spray itself can be hazardous: Montana had to evacuate herself from deep in the Wind River Range when her canister accidently went off in her tent, dousing her and all her gear with acrid, bright red capsaicin powder. (Unfortunately, once bear spray is deployed on fabric, it becomes a bear attractant, and a painful one. Montana dug through her first aid kit for some Pepto Bismol tablets, which she chewed up and rubbed on her face to quell the sting.)
Thanks to constant yodeling to announce our presence on trail, all the bears we met (including a sow with two cubs) seemed both unsurprised and unimpressed by us. Every one of them kept going about their business—digging roots and otherwise preparing for their long, hard winter of hibernation.
Pangaea Proxima: Imagine the Thru-Hikes!
Each year, volunteers organized by the Continental Divide Trail Coalition seek to establish and mark a little more of the trail. Over geologic timescales, the route will have to keep evolving to keep up with the constantly changing divide. “The Continental Divide in the Rocky Mountains will continue to dominate for millions of years,” Karlstrom said. “The rivers are going to keep trying to tear down the mountains, and they’ll succeed, over timescales of tens of millions of years.”
On even longer timescales—hundreds of millions of years—North America will join all the other continents in Pangaea Proxima, with the whole mass drifting south toward the equator. “We’re in a phase of collision right now,” Scotese said. “Africa is colliding with Europe, India just collided with Asia, Australia is colliding with the islands of Southeast Asia. You could almost walk across all the continents, they’re all connected in a tenuous way.”
It seems unlikely that any humans will be around in 250 million years to witness Pangaea Proxima—I hope there are still grizzly bears—but if there are, you can bet there will be a few intrepid thru-hikers aiming to cross the entire supercontinent on foot.
—Mary Caperton Morton (@theblondecoyote), Science Writer