Told first in a book, and later a movie, the story will be familiar - the hiker trapped in a nightmare scenario, who severs his own arm and lives to hike another day. But what went through his mind on the way to that extremity? And was he always heading towards some sort of macho mishap? If you're going to find self-knowledge the hard way, it doesn't come much harder than Utah's canyonlands, says Ronald Turnbull. 

Between a Rock and a Hard Place - Aron Ralston (2003)

127 Hours (film) - Danny Boyle (2011), with James Franco as Aron

There must be some fuckin chemical

chemical in your brain

that makes us different from animals

Free Blood 'Never Hear Surf Music Again' – '127 Hours' soundtrack

It's said that a wolf caught in a trap will gnaw its own leg off to escape. There's even some actual evidence for this. But what about a human being? That particular experiment has rarely been tried.

Aron Ralston, alone in a slot canyon in a really remote part of the Utah backcountry, clambers down a jammed boulder. It rolls over and traps his right hand. It's no spoiler to reveal that he comes out of the canyon without it: he's shown on the cover with his prosthetic iceaxe.

How did he find it in himself to do that? How much did it hurt? Would I be able to do the same? And, shall we always remember to always, always, leave a routeplan when we're heading off alone into the Utah backcountry?

Thinking – it's what makes us human. Aron spends two days building a pulley system with his abseil gear to lift the boulder off his trapped arm. The boulder weighs half a ton and the pulley system fails. In the eventual rescue of the severed arm, it would take 12 men, a winch and a hydraulic jack.

Meanwhile Aron's recording his last messages on his pocket video recorder – with the same slack facial expression on the pictures Joe Simpson and his companion took while dangling from a casually placed piton on the Walker Spur.

Going on in the background, the parallel story of his colleagues and friends gradually realising Aron hasn't turned up for work two days in a row, and his parents practically melting their landline as they track him down through ten thousand square miles of dirt trails and sandstone wilderness.

In the end it's a moment of blind rage and disgust – when he pokes his knife blade into his trapped thumb and releases the stinking gasses of decomposition. That's the moment when he acts, using the leverage and weight of his own body to snap each of his arm-bones, one at a time, so's to be able to cut himself free with his blunt knifeblade.

The cover blurb describes the book as 'like Touching the Void directed by Quentin Tarentino'. But it was actually Danny Boyle who turned this one into a movie. It came immediately after 'Slumdog Millionaire' and before the London Olympics opening; presumably he fancied a break from directing crowd scenes. It's a film you watch just on the basis of how the heck can he make a movie about one man and his arm, with the principle shooting location inside a rock canyon less than a metre across?

So this is a story with just one character. This unattached, 27-year-old, male, lover of the outdoors, whose reaction to an out-of-control glissade that nearly ended in a rockfield (p40 in my edition) was to go back to the top and do it again.

"You have been heading for this situation for a long time. Look how far you came to find this spot. It's not that you're getting what you deserve – you're getting what you wanted." (Know anybody like that, any of you male, unattached, 27-year-old readers?)

In fact Aron, with his new iceaxe arm, went straight back to his previous outdoor life, now financed by his new career as a motivational speaker for large corporations – the only lesson learned being the simple one of leaving a route plan. According to an interview in the Guardian in 2010, it was a breakup with a girlfriend, three years later, that triggered major life changes.

Danny Boyle's film is drama, not documentary. He introduces a small flash flood, he moves the 15-minute daily sunbeam to cover Aron rather than just the end of one of his legs. On the way into his canyon Aron comes across two hiking women and gossips about another canyon, one with a dropoff into an underground pool. Danny Boyle moves this cavern 100 miles to make it into part of the itinerary. He also rewrites all of Aron's monologue.

"Now is it true, that despite, or maybe because you're a big fucking hard hero, you didn't tell anyone where you were going? Uh, yes that is correct. Anyone? No. Oops!" That's Aron interviewing himself, on his own camcorder – as imagined by screenwriter Simon Beaufoy.

But at the same time, the portrait of Aron is true. True enough that the actual Aron Ralston, at the film preview, was reduced to tears by it.

And then there's the other true thing in this movie. It may be a simple story of a man losing his lower arm to find himself – this deeply self-centred person, this man who puts the outdoors ahead of other people. But then again – what an outdoors. A place that really is as spectacular as Danny Boyle's cinematography can make it. The weird, otherworldly, pink and beige landscape of Utah's slickrock deserts.

If you're going to find self-knowledge the hard way, it doesn't come much harder than Utah's canyonlands.