In the winter of 1994, while queuing to pay for a shovel in a Minneapolis hardware store, Cheryl Strayed picked up a book called The Pacific Crest Trail, Volume 1: California. The PCT, she learned, is a continuous wilderness trail that runs in a jagged 2,000-mile line from the Mexican border in California to a bridge spanning the Columbia River just into Canada. She put the book back on the shelf, and left.

At just 26, Strayed had a lot of shit to shovel. She had lost her mother to cancer, flunked college one paper short of a degree, been divorced from a husband she still loved, and generally thrashed about in the shockwaves of this extended trauma. Drifting from state to state for several years, she was now in Minneapolis where she waited tables and had sex with strangers. She was so far from the idea of herself she had grown up with that she had come, literally, to assume a new identity: when her divorce was finalised, she changed her (undisclosed) surname to Strayed.

Choosing a new name for yourself is both a symbolic gesture and a statement of intent, a strategic investment in the future. Strayed was a shrewd choice; it was clever not to choose Strays, which implies a refusal or inability to change. In a culture that rewards the remodelling of the self, "Strayed" is a canny piece of self-agency  a kind of directed lack of direction in which every signpost points to personal overcoming and a slot on the Oprah Winfrey Book Club.

Armed with a problem of existence and a surname that incorporated it, Strayed returned to the hardware store and bought the guidebook. She worked tables and saved and gradually assembled the necessary equipment and provisions (including condoms) for a solo hike along a section of the Pacific Crest trail that runs through California and Oregon. She packed supply boxes and arranged for a friend to mail them at intervals to post offices near the trail. Finally, seven months on, she took her first steps on the PCT, with the goal of reaching the Bridge of the Gods (redemption being on the agenda), a thousand miles to the north. Her backpack was so heavy she couldn't stand upright. She called it "Monster". Thus encumbered with a burden that could not be borne  she had become her own ugly baggage  she stumbled awkwardly on to the path of self-discovery.

What follows is a thoroughly artless transcription of personal history, a kind of anti-Kerouac memoir where the heat of immediacy is sacrificed, maddeningly, to the cooler demands of meaningfulness. A bear appears on the trail, runs off when Strayed blows her emergency whistle, but in which direction, ahead of her or behind? Cue existential sweat about walking the line (as in, you know, life), facing your fears, advancing rather than retreating. The bear is significant. For her. It exists, like everything else in what might otherwise have been a striking landscape, only as a subdivision of her own concerns. A fox looks at her. She whispers to it, "Fox". He ambles off, she calls gently, ruefully, "Come back," and when he doesn't she shouts "MOM! MOM! MOM!" The fox can't just be a fox, he has to be transformed into an integer of loss, a piece of mental taxidermy.

Long distance walking requires a kind of rhythm, and so does writing about it. Strayed has a tin ear for this, and keeps missing the beat. It is a singular achievement to describe a thousand-mile walk and leave the reader so far behind. She encounters a charging Texas longhorn bull, rattlesnakes, some more bears, she hears the yip-yip of coyotes at night, her toenails fall off because her boots are too tight, she loses one boot so has to walk in plastic sandals held together with gaffer tape, her skin chafes and bleeds under the heft of her pack, she is forced off the trail by record snowfalls, she meets a man and has sex with him, she meets other men and manages not to have sex with them  all this recorded in prose more broken and uneven than any wilderness trail. Oh for the tarmacadam of a single smooth sentence, with no slip roads leading into metaphysical dead-ends like this one: "What if what made me do all those things everyone thought I shouldn't have done was what also had got me here?" What?

Strayed reached the Bridge of the Gods, in case you were wondering. She found "the me inside of me". She has sold the film rights to Reese Witherspoon, with Nick Hornby, who finds this book to be "brilliantly written", supplying the screenplay. Oprah loves it and has welcomed Strayed to her industrial complex of self-transformation. Nice one Cheryl.

 Frances Stonor Saunders's The Woman Who Shot Mussolini is published by Faber.

In this hugely entertaining book, Cheryl Strayed takes the redemptive nature of travel  a theme as old as literature itself  and makes it her own. For three months she hiked 1,100 miles alone along the Pacific Crest Trail, a continuous wilderness undulating from Mexico to Canada over nine mountain ranges  the Laguna to the Cascades. She did it, she says, "in order to save myself".

An American raised in rural Minnesota, Strayed lost her beloved mother when she was 22. An abusive father had long ago vanished, and in the wake of their bereavement, Strayed's siblings and stepfather scattered and her marriage to a rather wonderful man collapsed as a result of her serial infidelities ("I'd smashed up my marriage over sex"). She was waitressing, servicing a student debt for a degree she failed to complete (she reckoned she would pay off the debt when she was 43), and then came Planet Heroin. In the wake of her divorce, she invented a new name for herself: Strayed. Because she had strayed. Four years after her mother's death, still "unmoored by sorrow", she packed a rucksack and flew to California. "Hiking the PCT," she writes, "was my way back to the person I used to be."

On her epic trek, this novice hiker faced temperatures of 100 degrees in the shade on the Modoc plateau and record snowfalls in the high sierras, not to mention bears, rattlesnakes and failed waterholes. The terrain was rarely easy: "Sometimes," writes Strayed, "it seemed that the Pacific Crest Trail was one long mountain I was ascending." Her boots died (she had already lost most of her toenails) and she made "duct-tape bootees" out of a pair of sandals while waiting for fresh boots to arrive in the middle of nowhere in a courier's box. When a branch snapped in the night outside her lonely tent, she made herself say out loud, "I am not afraid." For weeks she does not wash or wear knickers and, as a result, a shower at a lonely campsite turns into "an almost holy experience". The seasons change, and so does the landscape, but these pages contain little in the way of topographical description. It is the inner landscape that captures this unusual author.

The story of her past, and in particular her mother's harrowing death, unspools as a counter-narrative alongside the blisters and the bulky backpack she calls Monster. (The mother, clearly an extraordinary and inspiring figure, looms over this book like a ghost.) Wild follows Strayed's painful first steps as she averaged nine miles a day and learned how to use her gear (or didn't), to the happy weeks when her muscles were like ropes and she was lean, bronzed and hairy-legged. At staging posts on the trail  not towns but straggly outposts of civilisation  she picked up resupply boxes she had mailed to herself. Each contained $20, along with books, freeze-dried food and a clean T-shirt (she packed lacy underwear in the last box). At one point she describes herself as "hot, angry, sick of myself". I recognised that. How very sick of oneself one gets on the road.

Mostly, Strayed saw no one, but she is good on the peculiar intimacy one strikes up on chance encounters in strange parts, and the camaraderie on the trail, when freeze-dried noodles, Elastoplast and news of fresh snowfalls are exchanged in long nights around the camp fire. I enjoyed those passages immensely. Similarly, she writes well about the relationship one has with books when alone and travelling, though I was inevitably influenced in her favour by the fact that her writers are mine, notably Faulkner and Flannery O'Connor. The latter would have admired Cheryl Strayed. In the evenings, after making camp, she sat with a pot of noodles gripped between her knees, spooning food in one hand and holding a book in the other, reading by the light of her miner's headlamp as the sky darkened. "I grew stronger," she writes as the weeks unfold. In short, she read herself out of a hole. And what are books for, if not that?

Wild tracks the physical changes as a body gets turned inside out in three months, and more interestingly, the prose reveals Strayed's return to sanity. Body image is a component of this last transformation. The author refers at several points to issues with weight that dogged her past, and to her confused attitude to her own physical appearance. At one point, at a PCT campsite, she sees herself in a cracked mirror for the first time in many weeks, and ends up "wondering whether I was a babe or a gargoyle". Many women will recognise that particular experience, and might take heart from the resolution Strayed finds in the course of her trip.

Sex is a leitmotif: Strayed likes it, and had packed condoms. Men are sized up as soon as they walk into the campsite and on to the page. About two-thirds of the way through the book, congress finally occurs, spreadeagled against a boulder on a beach, with honey and sand involved. Sex is one of the last taboos in women's travel writing, and I have noticed that male reviewers tend not to like it. They know, I hope, where they can stick their dislike, and well done Cheryl Strayed.

Despite the Wagnerian tempests that led to the journey, a quiet dignity inhabits the heart of this book, as Strayed takes on the Mojave desert and the wind-twisted foxtail pines at the foot of Mount Washington. There are longueurs in the story and stylistic infelicities in the prose. But she lobs in lots of yeasty direct speech to keep the book, like the journey, on the road. I can't wait for the film.

Strayed is 44 now: one senses that it has taken her this long to understand the true meaning of the journey  or perhaps she had to wait for certain people to die. At any rate, she is happily married with two children, her demons at bay, and her book, a New York Times bestseller, was taken up by Oprah (you can watch a Strayed slideshow on the Oprah website). Towards the end of Wild, approaching journey's end at the Bridge of the Gods over the benighted Columbia River, the author writes: "I felt fierce and humble and gathered up inside, like I was safe in the world now." Lucky her.

Sara Wheeler's new book, O My America! Second Acts in a New World, will be published in March by Jonathan Cape