With his film version of “Ask the Dust,” Robert Towne returns to the milieu that made his name. An acclaimed screenwriter and occasional director in his own right (“Personal Best,” “Tequila Sunrise”), Mr. Towne is still most widely known for writing “Chinatown” (1974), one of the definitive screen portrayals of Depression-era Los Angeles.

The seeds for “Chinatown” were sown, in part, with John Fante’s “Ask the Dust,” a 1939 novel that Mr. Towne reportedly read as research 30 years ago, and which he’s worked to bring to the screen ever since. But in the interim, the spark of inspiration seems to have dissipated. While the book remains as vital as ever, the movie seems as musty as the bound volume that appears in its opening credits.

Mr. Towne, who wrote the adaptation and directed, isn’t alone in his devotion to this somewhat forgotten author. Unsuccessful upon first release, much of Fante’s writing was republished in the 1980s thanks, in part, to the lobbying of Charles Bukowski. Admirers have compared Fante’s remarkably direct prose to Ernest Hemingway’s, but his hard boiled clip can also be seen as a precursor to film noir. Indeed, Fante enjoyed a career as a screenwriter, albeit not usually in that style.

The semi-autobiographical “Ask the Dust” is one of the better books written about the agony of creating fiction, which explains its appeal to a scribe like Mr. Towne. But while Fante excels at evoking the texture of Los Angeles in the late Depression, his narrative isn’t particularly cinematic. The story is episodic, often free-associative, and essentially naturalistic, with a spontaneity and shapelessness that is difficult to pull off on screen.

“Ask the Dust” sees Fante’s alter ego, a 20-year-old writer named Arturo Bandini (Colin Farrell), seeking fame in Los Angeles, having just published a short story called “The Little Dog Laughed.” He longs for experiences to write about and finds them with Camilla (Salma Hayek), a Mexican waitress who, despite Arturo’s advances, loves a consumptive bartender named Sammy (Justin Kirk). In a twist typical of Fante’s cynicism – and reflective of Los Angeles in the 1930s – Sammy mistreats Camilla because of her ethnicity.

Mr. Towne, like Fante, depicts Los Angeles as a city of transient misfits, filled with characters like Mrs. Hargraves (Eileen Atkins), the owner of the hotel where Arturo lives, who “tries to make the whole lobby look like Bridgeport, Connecticut – no Mexicans and lots of doilies.” Hellfrick (Donald Sutherland) is a shell-shocked veteran who lives next door to Arturo, panhandling and helping his neighbor steal buttermilk. One of the more effective threads involves Vera Rivkin (Idina Menzel), an East Coast intellectual living in Los Angeles because an accident left her disfigured below the waist. In Vera, Arturo finally locates his inspiration.

One can sense Mr. Towne reconciling conflicting motives in “Ask the Dust,” with a desire to maintain fidelity to his source butting up against an eagerness to impose a personal stamp. The veil of Fante’s fiction has been lifted slightly – for instance, Mr. Towne has changed the name of Arturo’s editor in the book, J.C. Hackmuth, to that of Fante’s actual editor at the American Mercury, H.L. Mencken (whose letters to Arturo are narrated in voice-over by Time magazine critic Richard Schickel).

Much of the disappointment is visual, although Caleb Deschanel’s brown-hued cinematography gives the proceedings an appropriately nostalgic feel. With Bunker Hill and Long Beach no longer looking like they used to, Mr. Towne was forced to film in South Africa, and a half-dozen or so small-scale sets give the movie the curious aura of a diorama. Considering the criticism that “Chinatown” took in the acclaimed 2003 documentary “Los Angeles Plays Itself” – which advocated for a realistic portrayal of Los Angeles in the movies – Mr. Towne’s choice of location seems especially ironic.

One aspect of “Ask the Dust” that Mr. Towne seeks to bring to the foreground is the issue of racism, and the frowned-upon Camilla emerges as a genuinely tragic figure – demeaned even by the Busby Berkeley musical that Arturo takes her to see. Arturo’s own motivations (a mix of brashness and insecurity) receive little clarification from Mr. Farrell, whose cold-fish performance fails to convey the excitement of a writer who lives only for his work.

With Fante’s hardened and somewhat dated ending shirking conventional closure, Mr. Towne is at a loss as to where to take his film. He veers off in his own direction, seeking comfort in a tedious soft-core scene as well as the finality (and cliche) of a character’s terminal illness. This character’s valediction is distinctly un-Fante, and also unworthy of Mr. Towne. It’s as if, decades later, we were given a version of “Chinatown” in which Jack Nicholson’s J.J. Gittes was allowed to bid goodbye to Faye Dunaway’s Evelyn Mulwray.