Yellowstone National Park in Wyoming contains America’s most coveted natural treasures. With 3,000 square miles of unspoilt beauty, it is like nowhere else on Earth.

Yellowstone is home to more than half of the world’s geysers, fumaroles, hot springs and other related phenomena. The world’s first national park, and with 3,000 square miles of unspoilt beauty, Yellowstone is like nowhere else on Earth.

‘I sat there in amazement while my companions came up, and after that, it seemed to me that it was five minutes before anyone spoke.’ So wrote Charles Cook in 1869, recording his expedition’s dumbstruck arrival at the head of a 20-milelong, 350-metre-deep gorge, crowned by a mighty green cataract and flanked with steaming, hissing walls of crimson, mauve and yellow. Cook’s expedition had been despatched to the lonely Montana-Wyoming border after wide-eyed fur trappers and prospectors came back from the region with tall tales of hot waterfalls that rose upwards, of petrified forests and an alien world of fire and brimstone, which trembled underfoot and belched orange gas and boiling mud. Silenced awe became the Cook party’s default mode – it was all true. That such a well-trodden nation, by then already an established global superpower, should have secretly nurtured this extraordinary lost kingdom seemed almost unbelievable. For most, it still was: the US only accepted Cook’s account when a further expedition returned with irrefutable photographic evidence.

Approaching Yellowstone National Park, I can understand the scepticism. Wyoming is one of the larger states by area, but the smallest by population, dominated by the discouraging, dun-coloured nothingness of the High Plains. The scenery wakes up outside Cody – founded by and named after William ‘Buffalo Bill’ Cody – and suddenly I’m driving through mighty canyons and gilded forests. A huge-skied sunset lends every vista a cinematic majesty. This is an epic land fit for all-American movie heroes – from John Wayne to Bambi.

By the time I pass beneath the twilit pine-log eaves of Yellowstone’s eastern entrance, I’m beginning to channel Charles Cook, to grasp the sudden surge of protective pride that led to the 3,000 astounding square miles before me being enshrined – just two years after its resident wonders were proven to exist – as the world’s first national park. ‘Withdrawn from settlement, occupancy or sale,’ as the 1872 Yellowstone Park Act stirringly decreed, ‘and for the benefit and enjoyment of the people.’

The Lake Yellowstone Hotel overlooks a vast and placid body of moonlit water, its distant east shore smudged with the glow of a long-burning forest fire. Built in 1891, it exudes the genteel grandeur of a bygone tourist age, with a White House-grade portico, iron bedsteads primly clad in sheets, and an unapologetic absence of TV and air conditioning. Patrolling the endless corridors and cavernous reception areas, my lungs remind my head that we’re 2,500 metres above sea level. ‘We’re all suckers for nostalgia,’ says a uniformed receptionist. ‘Folk come here to see what their country used to look like and to experience it how those early visitors did.’ Though not exactly how. Just before the park’s fifth birthday, 700 Nez Perce Native Americans charged through Yellowstone in desperate flight from a US Army force ordered to corral them into a distant federal reservation. Twenty tourists were taken hostage and three killed, including one cut down in the doorway of his hotel. After a five-month, 1,000-mile pursuit, the Nez Perce eventually surrendered just 40 miles south of their goal – the Canadian border.

Even overlooking the perils that lay in wait once you arrived, simply getting to Yellowstone in the pre-railway age was a substantial undertaking. The reward that made it all worthwhile was first-hand experience of the park’s uniquely weird geothermal wonders. Yellowstone is home to more than half of the world’s geysers, fumaroles, hot springs and other related phenomena, and the sole founding purpose of Yellowstone National Park was to save them from mineral exploitation and the tacky intrusiveness that had recently despoiled Niagara Falls.

In 1872, The New York Times described the contemporary fascination with these ‘extraordinary and sometimes terrible manifestations of nature’, though back then they didn’t know the half of it. Only in recent decades have researchers established that the 40-mile circular area encompassing the world’s most famous geyser, Old Faithful, is a gigantic caldera – the collapsed cone of a super-volcano. Yellowstone erupts on average once every 650,000 years, in the process entombing half a continent under many feet of ash, and pitching the entire planet into a dark and poisoned volcanic winter. It last did so 640,000 years ago.

This knowledge lends a touch of portent to my tour of the park’s magma-related wonders. Old Faithful does its job, firing a glittering hot sheaf of water 30 metres into the blue sky before an amphitheatre of camcorders. More compelling are the sprawling geothermal areas of Norris and Grand Prismatic, boiled and flatulent prog-rock moonscapes fringed by sickly pines – both a retrospective of how Earth began and perhaps a preview of its apocalyptic end. No natural wonders are more gloriously unnatural: the crusted oranges and iridescent blues look as pure and wholesome as the run-off from a battery factory, with a reek to match.

Yellowstone’s administrators were oblivious to the park’s non-volcanic treasures until the late 1880s, when America abruptly woke up to the consequences of its rapacity. Ancient forests were disappearing across the nation and entire species were pushed to the brink of extinction – after more than two decades of unfettered slaughter, the native bison population had been reduced from countless millions to less than 1,000. ‘That’s always been the American way,’ says regular visitor and amateur naturalist Stacey Allen, peering through an enormous spotting scope across a flood plain dotted with browsing four-legged Chewbaccas. ‘We’re a country rich in resources and it’s still in our pioneering psyche to want to grab and exploit them to the full. It took real courage to draw a line in the sand here and say “enough”.’

By ring-fencing its volcanic attractions, the park’s directors had accidentally created a huge and suddenly rare nature reserve. To safeguard it against poachers, the military were brought in. In 1916, with a world war to fight and a massive surge of motoring tourists in Ford Model Ts to marshal, the army gave way to the newly created National Park Service. Today, the NPS oversees 58 national parks, from Alaska to Hawaii, together encompassing an area twice the size of England and attracting 300 million visitors annually. With its fleet of Toyota Priuses and a slavish devotion to recycling, the NPS is now a beacon in the smoggy gloom that enshrouds US environmental awareness, but its ecological stewardship took a while to mature. Yellowstone’s grizzlies were still leading the Yogi Bear life until the ’70s, being fed from car windows and encouraged to scavenge at hotel rubbish dumps for the entertainment of guests. Permitted fishing practice has only recently moved from ‘hook and cook’ to ‘catch and release’, and forest fires that were once hastily extinguished are now left to burn as part of the park’s natural regenerative life cycle. Half the hillsides are stacked with the blackened pine flagpoles left by a huge blaze back in 1988. Wolves, having been systematically eliminated, were reintroduced in 1995 – a missing link in a food chain then topped by the coyotes that were killing off the park’s pronghorn antelope.

‘We’ve got 12 packs now,’ says Stacey, with a proprietorial bearing earned through 10 consecutive wolf-spotting holidays at Yellowstone. He relates his epiphany with shining eyes. ‘On the last day of my first visit in 2001, I’m down the Lamar Valley with my wife when 25 members of the Druid Peak pack come right by us.’ He insists his wife’s as happy as he is to spend three annual weeks in Yellowstone, putting in 14-hour shifts squinting into an eyepiece. ‘But I acknowledge that the American male still likes to think of himself, deep down, as a frontier outdoorsman.’

There’s certainly a blokeish ambience about the park – a sense of flinty eyed, stubbled reconnection with one’s inner Davy Crockett. Tales of fatal misadventure – two hikers have been killed by bears in the last 12 months – are recounted with sombre relish, and plenty of teeth sucking at transgressions of good trail practice. Tracking a huge dark moose through a twig-snapping wood, I’m very glad of the neighbouring stalker who whispers that we’re safe. The unblemished black fur on those salad-server antlers indicates that the bull moose isn’t up for a fight.

People still come to Yellowstone for the geothermal action (‘I mean, how many times can you say you rode your bike round the rim of a volcano?’ says one of the many Harley-Davidson riders who file through at the stately 45mph speed limit), but they stay for the wildlife. Sprightly octogenarians Don and Jo Drain are up before dawn every morning, piloting their seven-metre recreational vehicle from a campsite just outside Mammoth Springs – the small town built for the park’s original military guardians – to one of Yellowstone’s fauna hotspots. ‘We’ve been coming here for a month every year for the past five years,’ says Don, dabbing his brow in the shade of his RV’s awning, ‘so we pretty much know the best places to see pronghorns, moose and wolves.’ And the best times to see them: ‘This is elk season. We saw a big bull with a huge rack put on a rutting display down by the river the other night – digging into the ground, urinating everywhere – one hell of a show.’ The Drains are familiar enough with the park’s ‘griz’ to know some by name. ‘Griz 264 is a superstar – he kills one or two elk calves a day. Then there’s the Five O’Clock Bear, who always comes out of the forest at that time. If you want to see bears, you need to be good at spotting a carcass – circling birds of prey, a little flash of white bone in the undergrowth.’

For the less dedicated naturalist, there’s a simpler technique: drive around until you hit a logjam of parked vehicles, then get out to see what everyone’s stopped to look at. Yellowstone’s roads cover just five per cent of the park, yet within a couple of days’ driving I’ve encountered every landmark species, except a wolf. A bull elk in the roadside pines, bugling hopefully, and rather effeminately, for a mate; a speckled osprey, posing for an hour on a conspicuous bough overlooking a lay-by; a moth-eaten coyote halfheartedly stalking a pronghorn, and most of the park’s 4,000 bison, rolling about in the dust, grazing in the dawn mist or ambling en masse up the tarmac, their huge minotaur-like heads brushing my wing mirrors. So confidently approachable does the wildlife seem – ‘cocky’ is Jo Drain’s word – that you begin to wonder if they’ve been bribed to satisfy the very low boredom threshold of any Disney-fed visitors who come expecting sights to be served up on demand.

A crowd gathered in Mammoth Spring’s churchyard leads me to a black (in fact very brown) bear asleep halfway up a tree. Someone says it was spotted by guests at an afternoon wedding, as the photographer marshalled the bride’s family beneath. National Park Service ranger Bridget Hand is on hand to make sure everyone keeps a safe distance. ‘Yellowstone is like a pocket wilderness, an accessible place for people who live in big cities and have never, ever experienced wildlife in a natural setting. I get asked where we put the animals at night.’

Alex and Danielle Sonsini live in the biggest American city of all, but as experienced national parkers they’re not likely to be asking too many stupid questions. It’s four weeks since they hitched a lovingly restored 1967 Avion caravan to their pick-up truck and set out from New York City, with venerable labrador, Augie, sitting between them. ‘A couple of years back we did a five-month trip all the way to Alaska and back, stopping in every national park along the way,’ says Danielle, who chucked in a high-flying career in IT to satisfy her wanderlust. ‘Out in these places you see unspoiled scenery, but you also find unspoiled people.’ Alex, a corporate chef turned sculptor, feels plugged into the oldest American tradition. ‘Our country was founded by pretty adventurous travellers, and then explored by pioneers in covered wagons. We never have an itinerary when we set off on a trip – it’s just about wherever the road takes us.’

It’s a comment that resonates throughout the balance of my tour. Yellowstone is more than a pocket wilderness – it’s a pocket planet, a theme park of iconic global scenery. Germanic pine forest, mouthwash-blue Scandinavian waterfalls, the Russian steppes, Mexican scrubland, boggy Gaelic moors and even a swathe of sub-Saharan savannah: it’s all here, reminding American visitors why they’ll never need to bother with a passport, and connecting them with the far-flung lands of their forefathers. They’re even getting round-the-world weather packed into a day, from sub-zero mist to wilting sun, via a couple of thundery hailstorms.

Yet at the same time, this place is like nowhere else on Earth. The Grand Canyon of Yellowstone, that psychedelic cleft in the land that reduced Charles Cook to jaw-slackened silence, might more convincingly belong in another solar system. At the Sonsinis’ suggestion, I round my trip off with another utterly incomparable experience: Boiling River, the only place in Yellowstone where you’re allowed to swim, and for much of the year the only place you’d want to. A half-mile walk from an anonymous car park follows the frigid Gardner River to its confluence with the aforementioned geothermal spring. Here, an artful arrangement of rocky pens blends the skin-flaying and bone-chilling waters. Each is home to half a dozen lolling bathers, their blissed-out, parboiled faces as red as the setting sun behind. They are at one with the volcanic heritage that secured this park its pioneering protected status and, in doing so, kickstarted the whole concept of environmental stewardship. ‘For the benefit and enjoyment of the people,’ I think, stripping down to my underwear and treading gingerly over the slippery stones to join them. Then I lie back with my head on a smooth boulder, gaze dreamily around at the lumpy brown hillsides and let the sulphurous warmth embalm me, a benevolent gesture from the volcanic gods before they blow us all to kingdom come.

The article 'The king of US national parks' was published in partnership with Lonely Planet Magazine.