The movie is based on the 2012 travel memoir, “Wild: From Lost to Found on the Pacific Crest Trail,” which is a detailed meditation on the politics of memory and a complex character sketch. “Wild,” however, despite a vivid performance by its lead, never entirely grasps the source material or its meaning. Director Jean-Marc Vallée (“Dallas Buyer’s Club”) employs a relatively simple flashback construct, which shows the audience Strayed’s life before the hike and turns her journey into a series of and alternately hazy and manic montages. Prior to embarking, Strayed lost Bobbi, her beloved mother (Laura Dern), to an aggressive form of cancer and her husband (Thomas Sadoski) to the emotional fallout from her subsequent affairs and heroin addiction. Bobbi is an unwaveringly loving mother who flees an alcoholic, physically abusive husband to raise her two children alone; she serves as a sort of beleaguered Madonna to the “whore” label assigned to Witherspoon’s troubled character. And Strayed is a well-read, self-aware feminist (she graduated magna cum laude from the University of Minnesota in Minneapolis with a B.A. in both English and women’s studies) who consciously becomes the protagonist of her own life on her own terms.