As actress Reece Witherspoon prepares to star in the true story of a woman who embarks on a gruelling solo 1,100-mile hike through the wilds of America, real-life heroine Cheryl Strayed reveals how a terrible grief fuelled the challenge. Her book, Wild, charts her journey from the Mojave Desert to Washington state, during which she faced rattlesnakes, black bears and the threat of mountain lions, in the hope it would help piece her life back together.

By Hannah Stephenson

In the basement of Cheryl Strayed's home in Portland, Oregon, hangs the Monster - a giant, worn and wizened old backpack she nicknamed because of its size - which acts as a poignant reminder of a journey that shaped the person she is today.

A lifetime ago, when Strayed was 26, separated from the husband she loved and shooting heroin with a new boyfriend she didn't, she made the most impulsive decision of her life: to take a three-month 1,100-mile solo hike along the Pacific Crest Trail (PCT) - from the Mojave Desert through California and Oregon to Washington state.

From the searing heat of the desert, to the ice-packed plains of the Kennedy Meadows, Strayed ploughed on with the Monster on her back, facing rattlesnakes, black bears, charging bulls, the threat of mountain lions and other dangers, in the hope that the experience would piece back together her life, which had unravelled.

But this is no travelogue. Four years earlier her beloved mother Barbara, known as Bobbi, had died from lung cancer aged 45. The trauma of that loss scattered the family. Strayed's brother and sister couldn't cope, her stepfather became distant and soon found himself another partner, and Strayed's world spiralled into self-destruction.

Her mother's death, and the resulting cacophony of grief, forms the beginning of Wild, a beautifully-crafted, heartfelt, thought-provoking memoir of Strayed's journey from lost to found, her battles with the wilderness and the demons in her mind.

"I cried my heart out while I was writing those chapters," she says of the sections which charted her mother's death, from the shock of the diagnosis to the final morphine-ridden end 49 days later. Strayed was 22 at the time.

A week later, she was unfaithful to her husband and, over the next few years, her marriage collapsed and her life went into meltdown. She ended up in an on-off relationship with a drug user called Joe.

"I had reached rock-bottom. I knew that this was not what I was meant to be doing. I was throwing my life down the drain. I was depressed and during that time I remember waking up in such despair. I remember thinking, if I continue to feel this way I'm not going to live."

On her last meeting with Joe, just days before the trip, Strayed recalls injecting herself in the ankle with heroin. The resulting bruise remained a stark reminder of the depths she'd sunk to.

She had no hiking experience. In the initial stages, her feet blistered, toenails fell off and her hips were rubbed raw from the straps holding up her oversized backpack. Of course, many a time she wondered what on earth she was doing.

"I would sometimes have the most gruelling, exhausting, terrible day and then I would sit there eating my little pot of dehydrated food looking across the most amazing land, with nothing in sight but the many colours of the wild, and just have this sense of how fortunate I was to be there at that moment and also that I'd gotten there on my own strengths.

"If I thought, I've still got 17 miles to go today before I'm done, I would despair. I'd try and think - it's a mile to that creek, where I'll stop for my chocolate bar. I had to make the goals small and the rewards many."

But the physical hardships helped alleviate some of the emotional agony she'd been feeling.

"I'd set out to hike the trail so that I could reflect upon my life, to think about everything that had broken me, and make myself whole again. But the truth was, at least so far, I was consumed only with my most immediate and physical suffering. Since I'd begun hiking, the struggles of my life had only fluttered occasionally through my mind."

Some 18 years later, her story has not only been a New York Times bestseller for more than six months and selected for Oprah Winfrey's influential book club, but Hollywood star Reece Witherspoon has bought the film rights and Nick Hornby is now writing the screenplay. As producer, Strayed will be a consultant on the movie.

"Reece was the first person to read it in Hollywood. She was looking for books featuring strong women. Then I got a call saying she wanted to option it and star in it. She's very perceptive and smart and I loved everything she had to say about why the story resonated with her," Strayed explains.

"I've met her too - she's very down to earth and funny and just like one of my girlfriends. I can see me hanging out with Reece."

Today, Strayed, 44, now a full-time writer, says she has learned to live with the grief of losing her mother.

"I'll always miss my mom. I miss my mom right now. I don't get to call my mom and say, 'Guess what? My book's coming out in the UK!' Or all those moments, like when I married my (second) husband and had my children, Carver and Bobbi - I don't get to share them with my mother, which is always sad. But I'm not ruled by my sorrow any more."

Hiking the PCT changed her.

"An experience like that is empowering. I used to get so much affirmation from things that don't really matter, like how I look and my sexual appeal. Here I was, fully involved in this physical and psychological thing, which gave me a deeper sense of self-worth.

"It gave me perspective about what we can endure when times are tough and the sense that the physical experience can be a way of dealing with emotions and trouble."

Strayed grew up in Minnesota, the daughter of a steelworker-turned-salesman who took his violent temper out on his wife until she left him, taking six-year-old Cheryl and her two siblings with her. Bobbi remarried a carpenter, Eddie, who had a great relationship with the children until Bobbi's death, when he drifted.

Despite her efforts, Strayed says she's been unable to reconnect totally with her siblings.

"We're not terribly close," she reflects, "but I love them and they love me. We live far apart. My brother's in Minnesota, my sister's in Florida and we have really different lives.

"I didn't realise how much my mother was the engine that drove the family."

Strayed now lives a few miles from the trail, and returns every year to do a section with her husband Brian Lindstrom, a documentary film-maker (whom she met nine days after completing the PCT hike), and their children.

"I always feel like I'm home again when I go there," she says. "I have a tender spot in my heart for that trail."

:: Wild: A Journey From Lost To Found by Cheryl Strayed is published by Atlantic Books, priced £12.99. Available now