She doesn’t look like you think she will — sun-dyed hair, dirt under her fingernails. She shouldn’t, of course: It was nearly two decades ago that she hiked the Pacific Crest Trail, brave and alone at 26.

But this is the image of Cheryl Strayed that has been immortalized in her memoir, “Wild.” Its cover — with its decaying hiking boot and Oprah Winfrey’s all-powerful stamp of approval — is omnipresent at airports and bookstores, two years after its publication. But that book jacket will soon change, replaced with a picture of Reese Witherspoon, face caked with earth. The Oscar winner plays Strayed in a new film about the author’s 1,100-mile solo trek on the Pacific Crest Trail, which she set out on in 1995 after her mother’s sudden death and the end of her first marriage.

Strayed, at 46, doesn’t look like you think she will because, standing in the lobby of the “Pretty Woman” hotel where she is staying, someone has put fake eyelashes on her. Her hair has been blown out, and she’s wearing motorcycle boots that hit midcalf. It’s October, and she’s just introduced Witherspoon at a fancy Beverly Hills luncheon. The actress, she says, has become a “dear friend.”

She walks outside and looks at the tourists and the line of sterile designer shops.

“So this is Rodeo Drive?” she asks, seeming disappointed. “It’s just all of these incredibly expensive stores.”

A few more paces. She points to an aubergine dress on a headless mannequin in the Dolce & Gabbana window display.

“Reese wore that,” she says.

Strayed has become better acquainted with fashion than ever before this fall, traveling with Witherspoon to promote the film at festivals in Telluride, Toronto and London. “I’ve never shopped more in my life,” she says.

She loves the film, and she loves its stars. As of late, her Facebook page has been filled with pictures of her looking chummy with the cast and posing on red carpets. “In case you were wondering,” she captioned one photo of herself sipping tea with Witherspoon, “I love this woman deep.”

The admiration appears to be mutual. Witherspoon posted the same picture on Instagram, writing that Strayed “is hands down the best author/friend/therapist any girl could hope for!”

According to Strayed, the pair had a connection the instant they spoke on the phone a few years ago. It was 2011, and “Wild” hadn’t even hit bookshelves. Strayed asked her literary agent if anyone in Hollywood might be interested in optioning her book. That was what most of her writer friends did — most of their books never actually got turned into movies, but they got a few thousand bucks out of it.

Witherspoon, as it turned out, was looking for stories for strong women. She devoured the “Wild” galleys in a weekend and immediately called Strayed.

“Reese and I talked — and that was important,” Strayed says. “I wanted to give it to somebody who wanted it for the right reasons. This book — I put everything into it. It’s me.”

The actress told the author how much the book had made her cry and promised she’d honor the story. But Strayed wanted to know more, especially about the kind of books the actress read. She took notes on Witherspoon’s favorite authors (Alice Munro, Amy Bloom) and felt an affinity with her when she realized the same books lined their shelves.

“I told her the stuff I’d admired about her too,” she recalls. “I was like, ‘I was on a bus in Guatemala and horrifically sick and having explosive diarrhea, and they were playing ‘Legally Blonde.’ And she was, like, ‘Great. That’s how I always want everyone to be seeing my movies.’”

Two years later, after Nick Hornby had adapted Strayed’s story for the big screen, it was Witherspoon’s turn to plumb the author’s depths. Strayed was on set for the majority of the 35 days that the production shot in Oregon, where she lives in Portland with her husband and two children. She served as a resource for both Witherspoon and director Jean-Marc Vallee, who could often be heard advising crew to “Ask Cheryl! Ask Cheryl!”

The answer that Witherspoon really wanted, though, was one that has stayed with most readers of “Wild.” Before Strayed sets out for her journey, she is sitting in a motel room, staring down her oversize backpack. When she tries to put it on, it’s so overstuffed that she literally cannot stand. It’s one of the more comical moments in the story: this twentysomething, completely unprepared except for her iron will.

“Reese would ask, ‘Why did you put on that backpack that you couldn’t lift? Why didn’t you take stuff out or say ‘… this, I can’t do it?’” Strayed says. “But it never occurred to me not to go. And that’s what ‘Wild’ is about. How we bear the unbearable. We’ve all been that person alone in a motel room with a pack she can’t bear that she has to bear.”

It’s this grit that has drawn so many to Strayed — both with “Wild” and “Tiny Beautiful Things,” a 2012 compilation of advice columns she wrote under the pseudonym Sugar for the website the Rumpus. And she’s facing what feels like another insurmountable challenge now: writing her next book. After “Wild” was an Oprah’s Book Club pick. And a New York Times bestseller. And got turned into a film from awards powerhouse Fox Searchlight.

“For a long time after ‘Wild’s’ success, I would say, ‘I don’t think it’s gonna impact me at all,’” she says. “But now I’m like, ‘Oh, can I write anymore?’ There’s that voice of doubt, like, ‘Maybe now you should just go live in a beach house and become a sailor or whatever.’”

She has started two potential books — one a memoir, the other a novel — one of which she plans to dive into after the film is released in December. She’s scared, but she’s not one to let insecurity overwhelm her.

“I’ve never wanted fear to be my ruler. I’ve just never been a person who was willing to have that be my narrative. Ever,” she says forcefully. “Maybe some of it is that I grew up poor and working class, and I had to do everything myself. I paid off my student loan from my undergraduate degree on my 44th birthday from the money I made from ‘Wild.’ Nothing was ever given to me. Except now I got a gift bag after this luncheon.”