Laura Dern stars in "Wild.” (Anne Marie Fox/Fox Searchlight)

Before she was cast in the movie “Wild,” Laura Dern had not read the best-selling book that inspired the film — “Wild: From Lost to Found on the Pacific Crest Trail” a searing memoir about author Cheryl Strayed’s transformative 1,100-mile hike after her mother died from cancer at age 45. So Dern, who plays Cheryl’s mother, Bobbi, sat down to read. And when she did, she said, “my heart completely cracked open.”

“Not only by Cheryl’s words as a writer and her story, but her shame-free look at her own life,” Dern said recently by phone. “Which I felt was so important.”

It was an intense reaction that surprised Dern, 47, known for her wide range of complicated roles in movies including “Blue Velvet” and “Citizen Ruth” as well as the HBO series “Enlightened.” Nothing has ever hit her quite like “Wild,” which is generating Oscar buzz in advance of its release Friday. The gutting story chronicles Strayed (played by Reese Witherspoon) as her life falls apart in the wake of her mother’s sudden death, setting off a chain of events, including affairs, a divorce and drug addiction.

In an attempt to find herself and regain some sense of reality, Strayed sets off on a grueling solo hike across the Pacific Crest Trail in California and Oregon. As she makes the exhausting journey, battling injuries, animals and some scary strangers, she is frequently visited by visions and memories of her mother, who was her best friend.

Bobbi, who appears in flashbacks during the film, is a complex character with a tough life yet a relentlessly optimistic attitude. It gets to the point where Cheryl (who has a more cynical worldview) is truly mystified about how her mother could find light in a world that can be so brutal. One of Dern’s favorite lines of dialogue is in a scene in which Bobbi is in the hospital undergoing chemotherapy. She looks out the window and says with genuine gratitude, “I always wanted a room with a view.”

“She was such an inspiration to me, as a mother and as a woman,” Dern said. “If you’re watching this film and you consider the kind of mother you want to be, she is quite the inspiration.”

Dern said she and Witherspoon, who already knew each other socially, bonded a great deal during production of the film, which was shot last fall in Oregon. One thing they discussed was that even though they had both done films based on true stories, it felt much different with the person right in front of you. During the filming of “Wild,” the real-life Strayed was on set about 95 percent of the time. Plus, Strayed’s daughter Bobbi (named for her grandmother), actually played the younger version of Cheryl in the movie. The whole process was a combination of unique, scary, magical and exhausting all at once.

“I don’t know how to put it into words,” Dern said of acting out Strayed’s real life while her family watched. “Every day, you’re staring behind the camera at the woman who did this, and the woman whose mother you’re playing that she lost. And you just feel a real sense of accomplishment to give her story its deserved honor.”

Similarly, director Jean-Marc Vallée (“Dallas Buyers Club”) hadn’t read “Wild” before he got involved in the project. After he read the script and then the book, he simply thought, “My God, I have to make this film.”

“With Cheryl’s character, I love the way she talked about herself, how really honest she could be and how beautiful that is — it’s rare to have read someone who talks about herself like that,” said Vallée of Strayed’s raw, frank details as she describes hitting rock bottom after Bobbi’s death.

Although the movie hit some roadblocks — including swapping shoot schedules thanks to last fall’s government shutdown, which closed national parks — Vallée said the crew “felt like kids going outside to play in the woods” as they filmed in gorgeous scenery. The exception to that: Witherspoon, who often had to film in freezing weather without a coat. (“Poor Reese!” Dern echoes. “I was freezing in my little parka, and she was just in a tank top and shorts.”)

Most of Dern’s scenes were shot at the end, but she still had to show up on the trail to film occasionally when her character appeared in Strayed’s dreams. Vallée says one of the most challenging scenes to film was when Bobbi died — the goal was not to overdo it, and to keep a respectful, delicate tone.

Again, it was only made more challenging by Strayed’s presence on set: But it was also a tragic blessing in some ways. Dern recently sat on a panel where someone asked Strayed about the most memorable aspect of the film, and Dern gets choked up just remembering the answer.

“I’m going to start crying, it was so moving to me,” Dern said, remembering the moment. “Cheryl said, ‘I got to watch my daughter get to know her grandmother through Laura. Because it’s a woman she’ll never meet otherwise.”