VOYAGEURS NATIONAL PARK — In a remote cove tucked along the northwestern shoreline of Namakan Lake, the 24,000-acre basin at the damp heart of Voyageurs National Park, stands one of nature's most remarkable achievements. It's a towering dam, perhaps 200-feet long by 15-feet tall, constructed from a veritable forest of dismantled trees. Its ramparts are sturdy enough to impound hundreds of thousands of gallons. It would do the U.S. Army Corps of Engineers proud.

This bulwark, though, was built by beavers.

I recently visited this colossus in the company of Tom Gable and Austin Homkes, wolf biologists from the University of Minnesota and National Park Service, respectively, who moonlight as beaver enthusiasts. We pulled up in a motorboat, the only way you can reach this distant inlet. I hopped out and, with some trepidation, clambered up the sloping dam, then tiptoed along its crest as if on a balance beam. Behind me stood a glassy pond, its surface studded with drowned pines; before me, thin air. I worried aloud that the dam might collapse, sweeping me away on an unleashed tide.

"Hey, if this thing breaches, we're all dead," Gable said cheerfully from the boat, which bobbed like a toy at the dam's base.

I shouldn't have worried: Although I weigh more than 200 pounds, I might as well have been strolling along the Great Wall of China. I welcome the discovery of other contenders, but it doesn't seem far-fetched to call this monolith the tallest known beaver dam in the world.

Standing atop that monument, the product of countless generations of furry construction workers, I felt a shiver of awe — the way normal people feel, I imagine, when they peer into the Grand Canyon. Unlike most visitors, who turn up with powerboats and walleye jigs, I'd been summoned to Voyageurs by a more obscure pastime: beaver watching. The park holds the unofficial title of supporting the densest population of Castor canadensis (aka beaver) in the Lower 48. As a longtime aficionado of semiaquatic rodents, I felt called to complete a pilgrimage to this, my personal mecca.

I was not disappointed. Over the last several years I've slogged through hundreds of beaver ponds in nearly 20 states, from Massachusetts to Michigan to Montana, and can state without reservation that Voyageurs boasts the most spectacular beaver infrastructure in the Lower 48. In eastern Washington, where I live, beavers are constrained by steep, tight streams; a big dam might stand 30-feet long and a modest 3-feet high. A colony of Voyageurs beavers? They'd whip that up before their birch breakfast.

For three days I traveled around Voyageurs, ogling architectural marvels with the boundless enthusiasm of a tourist in Rome. On the Kabetogama Peninsula, the park's largest landmass, the flat topography, sweeping meadows, and vast roadless areas combine to furnish an untrammeled beaver heaven. Gable and Homkes showed me dams that stretched 600 feet; dams that created wetlands larger than many farms; dams so old they had been swallowed by vegetation, like the ruins of Angkor Wat in Cambodia.

Beavers, of course, are renowned for their industriousness, but in Voyageurs I found myself equally impressed by their hydraulic savvy, their penchant for working as smart as they do hard. One 80-foot dam, built to span a narrow granitic canyon, restrained a 60-acre pond riotous with the calls of spring peepers and chorus frogs. If you asked a civil engineer to construct a dam that maximized storage while minimizing parts and labor, she couldn't pick a better spot.

Glimpse into a lost world

Since the arrival of the Ojibwe — who ate the flesh of the amik, wore its pelts, and enshrined it atop one of their clans — northern Minnesota has been tied to beavers. Voyageurs National Park draws its name from French Canadian fur traders whose navigation routes eventually formed the U.S.-Canada border. When these intrepid travelers first paddled the Upper Midwest, they encountered a beaver paradise. "What a wonderful thing to see the industrie of that animal, [which] had drowned more than 20 leagues in the grounds, and cutt all the trees," wrote Pierre-Esprit Radisson, a Hudson's Bay Company fur trader. Near Lake Superior, beavers had so thoroughly bogged the earth that Radisson, at the instruction of his native guides, crawled "like a frogge" to avoid vanishing into the swamp.

But Beavertopia wouldn't last. The voyageurs and other traders reduced millions of beavers to hats, virtually eliminating the species from the Lower 48. Neglected dams collapsed, draining ponds and wetlands. Without beaver-built speed bumps slowing and spreading flows, streams eroded to gullies and water tables plummeted. Much of our once-lush continent degraded to desert.

Luckily, you can't keep a good mammal down. Between 1940 and the 1980s, Voyageurs' beavers erupted, their comeback aided by fires and logging that regenerated new aspen, a staple of their diet. By 1986, the number of dams on the Kabetogama Peninsula had leapt from 71 to a stunning 835, while ponds and wetlands spiked 13-fold. The park's beaver population may never reach its pre-trapping heights, but it's not far off.

As Voyageurs' beavers have recovered, they've provided a glimpse into a lost, pre-colonial world — a land in which rodents, not humans, were the primary movers and shakers. On Kabetogama Peninsula, their influence extends even onto dry land. At one point, Gable and Homkes, the biologists, took me to a sprawling, treeless meadow — the footprint of a drained beaver pond. Now the site was sustaining another species: Wolves had taken up residence in the gargantuan lodge standing high and dry at the meadow's center. Elsewhere, ancient dams snaked across the forest floor like giant gopher tunnels, their crests studded with trees that once took root in an antediluvian wetland.

"Beavers are so woven into the fabric of what this place is — they're why the voyageurs were here," Steve Windels, a National Park Service biologist, told me during a tour of Kabetogama Lake's shoreline beaver lodges, which come in a bewildering diversity of designs and sizes. Windels has studied the park's beavers since 2006, ear-tagging more than a thousand in hopes of understanding their population dynamics. He's such a castorid connoisseur that he's been known to distill the animals' scent secretions and mix them with vodka. (It'll put fur on your chest.) "We've always recognized that cultural connection, but they also define this landscape."

Because the Kabetogama Peninsula's finest beaver work is accessible only by water, however, few Americans have seen these jaw-dropping phenomena. Most of the wetlands we visited required bushwhacking through spruce forests and bogs — lovely walking in late May, but black fly hell come summer. Perhaps someday the park service will see fit to create the Kabetogama Beaver Trail, Gable's idea for a grand hiking loop that links together the peninsula's ponds.

Such a trail would serve as a fitting tribute to these biological wonders. Voyageurs' beaver dams are treasures of the natural world, as important to our shared national heritage as Delicate Arch in Utah or California's redwoods. Yellowstone National Park has its bison, Glacier its grizzlies, Isle Royale its moose and wolves. And Voyageurs? It's got America's most ambitious beavers — and an open window onto our rodent-built history.

Environmental journalist Ben Goldfarb is the author of "Eager: The Surprising Secret Life of Beavers and Why They Matter," which published in 2018.