Over the course of its venerable history, Yellowstone – America’s “wild wonderland” – has become the most iconic nature preserve on Earth, a place of pilgrimage for generations of travelers. Yet never before has the world’s first national park felt the squeeze of so much human adoration as this year.

On many days, traffic stretches for miles outside the busiest park entrance at West Yellowstone, Mont. Once motorists pass through the gate, they confront more congestion traveling to Old Faithful, often in the form of “wildlife jams” whenever there is a bull elk, grizzly bear, or buffalo roaming the roadside. These moments are usually accompanied by camera-clutching tourists lunging out of their cars and racing toward the animals as if they were cuddly denizens of a circus menagerie. Finally, upon reaching the famous geyser, the visitors find, in the middle of the remote West, a Yankee Stadium-sized parking lot that is often full.

But then something remarkable happens. As the throng waits for Old Faithful’s steamy plume to rumble out of the earth, a mood of reverence sweeps over the crowd. When the geyser at last gushes skyward on its magical and mysterious 90-minute clock, the visitors gasp and erupt into applause, solidifying a pluperfect moment likely to be remembered the rest of their lives.

ANN HERMES/STAFF Throngs of tourists capture the primordial spectacle with cameras and cellphones as the geyser spouts into the air on its magical and mysterious 90-minute clock.

This, says park superintendent Dan Wenk, is one of Yellowstone’s many strange and inspiring paradoxes in the 21st century. In an age of iEverything, when people incessantly tap electronic devices and dwell in various forms of virtual reality, national parks offer a singular and natural counterpoint.

Last year, Yellowstone hit more than 4 million visits for the first time in history. It is poised to significantly surpass those numbers in 2016, the centennial year of the National Park Service. But behind all those cars and tour buses in the land of lodgepole pine looms a fundamental question: Is such soaring popularity good or bad for Yellowstone – and, more broadly, for the national park system as a whole? Can America’s outdoor crown jewels survive unmarred for another 100 years?

“The question many are asking,” says Mr. Wenk, “is can Yellowstone escape from being loved to death? My answer is yes, I believe it can. But Yellowstone won’t be saved if we stay on the same course.”

ANN HERMES/STAFF Ranger Julie Stetson leads a hike on Taggart Lake Trail as part of an educational program available to visitors at Grand Teton National Park in Wyoming.

The National Park Service officially turns 100 years old Aug. 25. The much-hyped centennial is not only a birthday celebrating what the late writer Wallace Stegner called the best idea this country ever had. It is also a time of profound introspection, even worry, for an agency entrusted with overseeing one of the world’s most spectacular collections of outdoor sanctuaries.

Critics say the Park Service – beleaguered by deteriorating roads and buildings, threats to natural resources, overwhelming public use, and the potential effects of climate change – is ill-equipped to steward its 411 parks, cultural sites, and historical monuments forward another 100 years. They believe the sacred national park experience that so many people journey to see has already vanished at some of the most popular destinations and will only get worse without a serious infusion of money and a rededication to preservation.

“I think the National Park Service is facing a crisis of conscience and confidence,” says Jeff Ruch, executive director of Public Employees for Environmental Responsibility (PEER), a vocal watchdog of public land-management agencies.

Yet all is hardly dire. The spirit of the parks and their ability to be a balm for an increasingly hyperkinetic world in many ways endures. Terry Tempest Williams, counted among the greatest living writers of the American West, set out on an exploratory mission a few years back to identify the essence of national parks. Ms. Williams visited a dozen big wildland preserves, historical sites, battlefields, and birthplaces of prominent citizens that are all part of the park system. What she discovered is spelled out in her new critically acclaimed book, “The Hour of Land: A Personal Topography of America’s National Parks.”

“Our national parks are breathing spaces in a country that is increasingly holding its breath,” she says in an interview with the Monitor. “We see the violence in the latest mass shooting in Orlando. We know the kind of madness a world at war with itself breeds. It is easy to fall into despair. But then, we stand before El Capitan in Yosemite Valley or look out across the vast erosional beauty of the Grand Canyon where we can see the curvature of the Earth, we are returned to a sense of wholeness in the world – an enduring beauty that will not only survive us but inspire us to be our highest and deepest selves.”

Reflecting on her own childhood spent amid the saw-toothed majesty of Grand Teton National Park, Williams doesn’t see America’s premier wilderness areas as doomed. What they need, she notes, is more citizen defenders lending their voice as advocates. “Our national parks allow us to remember what we have forgotten – that we are a part of nature, an extension of nature, products of nature, not separate from it,” she says. “And how we take care of parks says a lot about ourselves.”

ANN HERMES/STAFF The Teton Range looms at sunrise from the Blacktail Ponds Overlook in Grand Teton National Park in Wyoming

Many people will be witnessing for themselves what the parks say about America this summer. Visitation in 2016 is expected to approach 315 million people, the equivalent of the entire population of the United States. More than 307 million people traveled to the parks in 2015 – up 25 million from just three years ago.

They come for a multitude of reasons – to introduce the next generation to the splendors of the wild, to revisit a memory of their youth, to hike in alpine meadows, to lift themselves out of lives circumscribed by a cubicle.

Emma and Pete Brawn from Ohio brought their three young sons to explore the grandeur of Grand Teton and Yellowstone. Ms. Brawn first visited the two parks with her parents several decades ago. Now she wants her children to experience the transcendence of moose and mudpots for themselves. The family is spending 10 days in the area and has unplugged from the internet and hiked deep into the backcountry, away from the clamorous crowds.

“I think, with having kids, it’s important to share the natural wonders of our country and the world,” says Brawn, a veterinarian. “Parks are an important way to protect our common heritage so generations to come can enjoy these remaining pieces of the Earth that seem lost in time.”

While the parks remain a popular vacation spot for families, the national origin of many of them is changing. More foreigners are among the legions taking in America’s outdoor haunts. On any given day, the conversations around Old Faithful sound like the United Nations General Assembly, as tourists exult about the primordial spectacle in German, Spanish, French, Japanese, Mandarin, and myriad other languages.

ANN HERMES/STAFF Bison create a traffic jam in Yellowstone – a common sight in the country’s oldest national park.

Asian tourism in particular is booming as states such as Wyoming actively promote the parks to people in the Far East. Recent data show that a few years ago 300,000 visas were granted to visitors from mainland China. This year US officials gave out more than 500,000 visas, and the travelers identified Yellowstone and Grand Teton as top destinations. In July, for the first time in history, Yellowstone hired three Mandarin-speaking rangers.

Many conservationists blame the aggressive marketing as one reason for the current crush of visitation. Others see a different kind of problem in the legions of people touring the parks today – a dearth of American minorities. The volume of Asian visitors to Yellowstone and Grand Teton National Park is now believed to be greater than the total number of nonwhite Americans who visit them.

The lack of diversity among American park travelers is something that particularly distresses David Vela. The superintendent of Grand Teton National Park, who is of Hispanic descent, says he seldom sees “people like me” reflected in the multitude of tourist faces. Even though Jackson Hole, Wyo., the gateway community to Teton, is more than 25 percent Latino, just 2 percent of local Hispanics actively use the park.

A 26-year veteran of the Park Service, Mr. Vela is the son of working-class parents who grew up in a small southeast Texas farming community. “The concept of national parks was foreign to us. And if we encountered Park Service rangers in uniform we didn’t know what entity they represented,” he says.

Although his parents had never been to a national park, they felt compelled to embark on a trip to Yellowstone and Grand Teton because many other local families were making the pilgrimage. “When we arrived in Grand Teton, I didn’t understand why it was protected and when I discovered the reason, that it was done on behalf of all people, for current and future generations, it was a powerful message,” he says. “Just one visit to a national park was life changing.”

Unfortunately, the idea behind the parks is something that isn’t always communicated effectively. “We have to change the dynamic – how people relate to parks – and to do that we need to start reaching young people early,” says Vela, who often makes visits to elementary schools to tout America’s wilderness areas. He’s cementing the tradition in his own family by teaching his five grandchildren that they have a place in parks.

“I have seen the transformative power of parks through my career,” he says. “After 9/11, Americans returned to their roots. They sought out national parks. Parks provide opportunities in times of great sorrow and despair to reenergize the American spirit and bring people together.”

ANN HERMES/STAFF Two elk, a common site at Yellowstone National Park, stroll through the lodgepole pine woods.

The parks are also reenergizing regional economies. Visitors to the various units of the park system generate about $32 billion in economic activity each year and are responsible for at least 295,000 jobs, according to the Park Service. For every dollar the federal government spends on national parks, it generates $10 in economic activity.

Yellowstone and Grand Teton alone produce more than $1 billion in regional tourism annually. The recovered populations of grizzly bears and wolves, which help make both parks arguably wilder than they were a century ago, are among the marquee attractions.

Yellowstone’s profile has never been higher. Chris Johns, chief content officer of the National Geographic Society, and Susan Goldberg, editor in chief of the magazine, believe it provides a lens on the meaning of the parks in the 21st century and America’s relationship with nature. The magazine devoted the entire May 2016 issue to the 144-year-old park, and it’s been one of the most widely read issues in the publication’s history.

Yellowstone is a concept that continues to evolve and be shaped by changing human values, says writer David Quammen, who penned the entire issue. The park was once revered for holding a collection of natural curiosities. Now it’s a landscape set apart for its full complement of wildlife, geothermal, and other phenomena that have vanished from most of the rest of the world.

“Yellowstone Park, and the Greater Yellowstone Ecosystem, represent the fullest and richest embodiment of nature within the contiguous 48 states, and therefore the central test case of America’s concern for other creatures and for the ecological processes that sustain them,” Mr. Quam-men says. “This is about more than national parks. It’s about how we as a nation of free citizens, with responsibilities as well as privileges, choose to live on a planet that doesn’t exist just for our convenience.”

It doesn’t matter that Yellowstone, in a way, originated as a means for railroads to drive more passenger traffic to the West. To conservationists, it has morphed into a symbolic statement that total human conquest of nature should not happen.

Michael Finley is the only Park Service veteran to have served as superintendent of three major national parks – Everglades, Yosemite, and Yellowstone. He says parks are about doing what’s right even when politicians say no, as with wolves, which were restored to Yellowstone over opposition from members of the congressional delegations of Wyoming, Montana, and Idaho.

“The miracle of Yellowstone is the reintroduction of the wolf and the biological cascade that has occurred by restoring a keystone species, which has benefited a range of other animals,” says Mr. Finley. “The risk to Yellowstone is the same as what I saw in the Everglades. There seems to be an ideological belief that little impacts on the environment don’t adversely affect the park. But as we saw in the Everglades, the ecosystem didn’t become partially disabled by a single swift blow. Similarly, in Yellowstone, it will be the cumulative effects of 1,000 seemingly little assaults upon the ecosystem that will render the real damage to Yellowstone and its surrounding wildlands in the future.”

He acknowledges there are big challenges, too. One is the chronic underfunding of the Park Service. It faces a $12 billion backlog of deferred maintenance – broken fences, bad roads, rickety buildings, damaged trails, deteriorated campsites. In Yellowstone alone, the amount of road reconstruction and building repair needed is estimated to be more than $600 million: Engineers say, at current funding rates, it will take 50 years to get it all done.

Encroaching development remains a constant threat as well. Author Williams says much of the public doesn’t realize that oil and gas firms are currently drilling in a dozen parks and seeking to drill in another 42.

In Big Cypress Natural Preserve in Florida and Cape Hatteras National Seashore in North Carolina, controversies swirl over the use of all-terrain vehicles. On the outskirts of Denali National Park and Preserve in Alaska, many people want to kill wolves to control their populations, and mining interests have long wanted to gain access to Yellowstone. Nearly every park faces some kind of land-use or wildlife-management issue.

Climate change represents a more subtle and uncertain danger. It is already blamed for melting Glacier National Park’s namesake ancient ice fields. It could eventually affect water flowing through the Grand Canyon and is likely to leave coastal parks, including the Everglades, under rising seas. Ecologists say it will lessen parks’ abilities to sustain healthy wildlife populations, and, in the West, may trigger larger forest fires that transform landscapes.

ANNHERMES/STAFF Historic buildings known as 'Mormon Row,' built by Mormon homesteaders in the early 1900s, are now preserved for visitors in the Antelope Flats of Grand Teton National Park.

Yet the crush of visitors remains one of the most pressing issues facing the nation’s premier wilderness areas. Everyone wants people to experience the majesty of the parks, but the question becomes: When does the adoration become too much?

Already, managers at Arches National Park in Utah have closed the park from time to time to control the number of visitors. At nearby Zion National Park, officials have implemented a bus service to alleviate traffic congestion, which has resulted in long lines to catch the shuttles.

“If we’re not past the point of no return in some of our parks, then we’re close to it,” says Jack Turner, a former university philosophy instructor who has worked in the parks for 40 years, mainly as a mountain climbing guide instructor. “Yosemite Village is as crowded as New York City or Calcutta. People who rent bicycles wanting to get out of their cars and not pollute can’t ride them because it’s turned into such a human anthill. It’s appalling what we’re doing to these places that we claim to hold as sacred.”

Few places feel the press of humanity as much as Yellowstone. The summer season here now stretches from May 1 to Oct. 1 – two months longer than it did just 20 years ago. Rangers are often overwhelmed as they deal with the growing catalog of tourist misdeeds. In 2015, Yellowstone staff issued a record 52,036 resource warnings to visitors, for infractions ranging from walking on delicate geothermal features (which can also be dangerous) to getting too close to wildlife. Last winter, superintendent Wenk sent letters to 85 bus tour companies, warning them that their clients are expected to abide by park rules. The missives were inspired in part by reports of some bus drivers pulling over alongside the road, handing passengers rolls of toilet paper, and instructing them to use the woods.

One Canadian tourist recently picked up a bison calf and loaded it into his SUV, bringing it to park rangers because he thought the youngster was cold. It later had to be euthanized after biologists were unable to reunite the buffalo with its herd.

“For a lot of visitors, this is an alien environment because so much of the rest of the country, so much of the rest of the world where they come from, is manicured, manipulated, tamed, and artificial,” says Lee Whittlesey, author of the book “Death in Yellowstone: Accidents and Foolhardiness in the First National Park,” which chronicles more than 300 fatalities in the park’s 144-year history. “Their idea of a park is Disneyland.”

All this is one reason Yellowstone recently hired its first social scientist, Ryan Atwell, to start gathering information on the motivations and behavior of people coming to the park. Wenk’s hope is that it will eventually lay the foundation for possible changes in how tourists navigate Yellowstone. Among the options: instituting a reservation system during peak season, deploying more public transportation such as shuttles, and creating zones in the park that have different visitation thresholds.

“We don’t have a wildlife-management problem,” says Wenk, sporting a Smokey Bear hat and whisk-broom mustache. “We have problems and challenges managing people. And the least studied species in Yellowstone is Homo sapiens.”

Indeed, during the summer, Wenk acts as a big-city mayor as much as he does a park superintendent. He has to contend with crime, suicides, drug dealing, poaching, car accidents, and lost visitors. In a one-year span between 2014 and 2015, vehicle accidents with injuries were up 167 percent and emergency transports out of the park jumped 37 percent. In 2014, national parks in general recorded 15 murders, 162 sex offenses, 358 assaults, and 3,000 thefts.

The rising crime has come as park staffing has declined. Internal Park Service figures secured by PEER show that from 2005 through 2014 the number of permanent law enforcement rangers dropped 14 percent. During the same period, seasonal rangers – the workhorses of the agency – fell 27 percent.

This has contributed to a decline in morale at an agency once considered the gold standard among government employees. In one of its recent annual surveys, the Partnership for Public Service ranked the Park Service 259th out of 320 federal agencies as a good place to work. It hasn’t helped that the agency is struggling with a scandal. Environmental activists and members of Congress have criticized the Park Service director, Jon Jarvis, for not doing more to address evidence of sexual harassment at Grand Canyon, Florida’s Canaveral National Seashore, and other parks.

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Still, for all the problems besetting the parks in general and the agency in particular, America’s outdoor cathedrals have proved remarkably resilient – and, across all generations, retain their sacred appeal.

Consider the Brawn family, sitting on the rim of Old Faithful, waiting for another hissing performance from Earth’s most famous blowhole. The two boys tick off what they’ve seen the past few days. They’ve memorized the eruption times of different geysers. They’ve seen grizzlies, black bears, elk, bison, and moose. “I had the best day of my life because I saw my favorite animal – a bald eagle – fishing for trout along the Firehole River,” says young Owen.

Nathan Varley is familiar with that kind of epiphany. The son of Yellowstone’s former science chief, he grew up in the park and has witnessed the reintroduction of wolves and rebound of the grizzly population. He now runs Yellowstone Wolf Tracker, a safari company based in Gardiner, Mont., that takes clients on wildlife tours. He sees how the magic of the park affects people every day. He urges them to let go of the “superficial culture of selfies” and look humbly through a high-powered spotting scope at a pack of wolves and pups at a distance, interacting without regard to people.

“If I can get them to do that, they slow down and it deepens their experience by getting them to live in a moment,” he says. “To me, this is what I want them to take home from Yellowstone.”

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It’s the kind of redemptive value of the parks that deepens human experience and, as Williams puts it, says something about America’s national identity.

“Our world expands with the vistas before us,” she says. “Our national parks are places of pause – an ongoing prayer of hope for our better future.”