Directed by Jean-Marc Vallée. Starring Reese Witherspoon. Rated 14A.

Wild is a ploddingly constructed take on Cheryl Strayed’s best-selling memoir of three months spent hiking the Pacific Crest Trail, from the Mojave Desert to the border of Washington state, after a bad personal patch in the early ’90s. The future author had just lost her beloved mother to cancer and responded by drifting into a haze of drugs and promiscuity.

Reese Witherspoon, who also coproduced this two-hour trek, plays Strayed, 26 at the time of her journey. And her mother, seen in extensive, persistently interrupting flashbacks, is played by a particularly frenetic Laura Dern, only nine years older than the star. That’s less important than the fact that this is Laura Dern, late of Enlightened and David Lynch movies, so when the woefully underprepared Cheryl starts seeing her behind sequoias and in garish dream sequences, Wild, at heart, becomes a kind of horror movie.

We’re never given much insight into why the loss of Cheryl’s mother, or her history with an abusive father, led to shooting heroin or screwing guys behind dumpsters while married to an increasingly confused fellow (The Newsroom’s Thomas Sadoski). Still, these vignettes give screenwriter Nick Hornby, who used to be clever, plenty of opportunities to break up all that hiking, explained as a way to “walk myself back to being the woman my mother thought I was”.

Aside from quotes from Robert Frost and Joni Mitchell left in parkside logbooks (each attributed to the author “and Cheryl Strayed”), there are few clues as to what makes Strayed want to be a writer, outside of the self-help impulses on display, and no sense of her talent for it. What we get is far more literal than literary, and this fragmented effort is satisfied with pretty ordinary observations, supported by more predictable music choices than we usually get from Jean-Marc Vallée, who did song-intensive films like C.R.A.Z.Y. and Café de Flore before his Dallas Buyers Club breakthrough.

What the film does well, in no small part through Witherspoon’s intense performance, is to convey the numbing varieties of sexual menace most women experience as a constant drumbeat when out in the world on their own. In that way only, Wild lives up to its name.