Hundreds of layers of red rock soar upwards, making it look like a corkscrew has twisted its way through the grotto. Unless planning to abseil down into it, the only way in is climbing up the muddy river bank, then fighting through thick, overgrown bushes. "Every year, we hold classical music concerts in here. The acoustics rival the Carnegie Hall," says the boatman. "Now imagine trying to get through while carrying a baby grand piano …"
We're just inside Canyonlands National Park, which covers a vast swathe of desert wilderness in south-eastern Utah. The park celebrates a stately 50th birthday this month, but its steepling Navajo sandstone canyons, cut over the centuries by the Colorado and Green rivers, are only fleetingly tamed. This is a destination for multi-day whitewater rafting expeditions and fully-kitted, self-sufficient hikers.
Coming in by boat along the Colorado gives a brief taste of the towering intimidation from the canyon floor, but the colossal scale of the sliced-apart landscape is best taken in from above. From the Island In The Sky mesa, a brutally barren horizon unfolds, cut by deep, plunging veins. It demands hours of leaning entranced over the clifftop railing, but this is the sort of humblingly extraordinary view that Utah seems to throw up as standard practice.
Of the five national parks that stretch out across the virtually empty southern half of the state, Zion is both the most visited and most accessible. A two-and-a-half hour drive from Las Vegas, this is Utah for beginners. A shuttle bus down the main canyon links trailheads and lookouts, and enormous bulging outcrops cast shadows over the narrow paths following the Virgin River. On top of said outcrops, many hundreds of feet above the canyon floor, the tiny figures of striding hikers can be just about identified.
Zion is gloriously photogenic, but it turns out to be a mere introduction – and the road out offers clues of what is to come. Highway 9 is a vertigo-defying exercise in climbing the canyon wall, emerging on a high desert plateau. By the time Rainbow Point in Bryce Canyon National Park is reached, the air is considerably thinner, and the elevation has sneaked above the 9,000ft mark.
It's an escalation in both height and drama. From the rim, a vast, seemingly untouched valley spreads out. Mesas, buttes and mountain ridges fight for attention, but their close relationship can be seen from the strata in the rock. Time may have created gaps between the formations, but the layers match up almost perfectly.
Bigger curiosities are found closer in. On the slopes inside the rim are thousands of hoodoos – rock formations that look like an army of supersized Nik Nak crisps. Formed in a similar way to the fairy chimneys of Cappadocia, years of wind, rain and winter snow have eroded the rock. The softer layers have succumbed first, though, leaving the bobbled effect and the illusion of free-standing weirdness.
Beyond Bryce Canyon, the road trip seems to take a shift in character. A sense of briefly detouring from normality gives way to out-on-your-own outback conquest. Highway 12 – nicknamed the Million Dollar Highway – gingerly teeters along ridge lines, peering down into a thoroughly uncompromising moonscape. Signs at the lookouts explain that the Escalante region we're passing through was the last place in the 48 contiguous US states to be mapped. It's as remote and geographically hostile as mainland America gets, with the swerving road following the route the pioneering cartographers used to force their way in.
Highway 12 eventually clambers downwards and joins the Capitol Reef National Park, often the forgotten brother of Utah's Big Five. It's here that the landscape is at its most Australian. Scorched red, rubbly earth is broken by only the hardiest of vegetation; tongues are sapped dry in kiln-like, humidity-bereft heat; an ancient uplift in the Colorado Plateau creates a gigantic, craggy rock wall as the only source of shadow.
The sweaty, dusty route through nowhere eventually leads to Moab, a marvellously out-of-place town fuelled by vegetarian restaurants, microbrewed beer and adventure sports outfitters. Moab is the gateway to both Canyonlands and Arches National Parks, and it's arguably the latter that provides the most gleefully digestible southern Utah highlights package. It packs in ridge-top panoramas, plateaus resembling solidified sand dunes, monumental rock formations that look like mutant pigs or elephants, and the ubiquitous rust-red cliffs. Then, of course, there are the natural arches that give the park its name.
From the road, Double Arch doesn't look all that domineering. But walking up to it, the scale of the monster becomes apparent. The main arch of the interlinked pair has a span of 160ft and a height of 108ft. To know how it was actually formed would probably spoil the moment. If there's one thing that driving through canyons and stark, rough-hewn desert teaches you, it's that there's an awe-struck happiness to be found in simply feeling dwarfed.
British Airways (0844 493 0787; ba.com) and Virgin Atlantic (0344 209 7777; virgin-atlantic.com) fly non-stop from Gatwick to Las Vegas. BA also flies from Heathrow, while Virgin flies from Manchester. American, Delta and United offer links via their hubs in the US.
Utah's five National Parks can be tackled as part of a loop from Las Vegas, taking in Monument Valley and the Grand Canyon on the way back.
The quickest routes are rarely the most spectacular. Taking in the scenic byways, the journey should cover around 1,200-1,300 miles. When planning overnight stops, bear in mind there is a substantial amount of driving involved in getting around inside the parks.
The "America The Beautiful" pass, allowing the holder and all occupants of the holder's car access to all US National Parks for a year, costs $80 (£50). Buy it online at nps.gov or at the first National Park you visit. Allow at least half a day per park – longer if you plan to take on hiking trails, boat trips or other activities.
The half-day Canyonlands boat trip offered by Tag-A-Long (001 435 259 8946; tagalong.com) costs $79 (£49).
Visit Utah (visitutah.com).
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