On September 11, 1857, after a five-day siege, more than 100 California-bound emigrants temporarily camped in Southwestern Utah were slaughtered by members of a Mormon militia accompanied by American Indian Paiute warriors. Historical consensus is that the tragedy, known as the Mountain Meadows Massacre, was a catastrophic byproduct of mounting tensions between the American government and the Mormon settlers who had come to the Utah territory a decade earlier seeking a safe haven from violent persecution.

At the time of the massacre, some 2,500 American troops had been sent to Utah to enforce a regime change ordered by President Buchanan that would remove territorial governor and Mormon leader Brigham Young from power. While most of the territory’s Mormons fell prey to rumor, assumed the worst, and steeled themselves for an invasion and military occupation, a small number actually did the worst and spilled innocent blood on Mountain Meadow one awful autumn day.

According to “September Dawn,” a film by Christopher Cain opening today, the Mountain Meadows Massacre was not the dirty work of John D. Lee, the man who confessed to inciting the Paiutes and ordering the mass murder, and was subsequently tried and executed for his crimes. Instead, the film insists that the settlers’ deaths were part of a conspiracy that figuratively bloodied Mormon hands all the way up to Young himself.

“September Dawn” supports this point by grafting Lee’s posthumously published denunciation of the church elders he claimed had approved the Mountain Meadow murders with a fictionalized Romeo and Juliet love story. The resulting patchwork of fervently anti-Mormon historical innuendo and period romance is so sanctimonious, gooey, and earnest that it plays like a low-budget, landlocked “Titanic.” It’s neither factually persuasive nor dramatically compelling. .

“Two different worlds met on this spot — one of love and one of hate,” says a survivor (Krisinda Cain, daughter of the director) of the massacre as she revisits the scene of the crime decades after the fact and shortly after the film’s opening credits. Beginning with a stumble, “September Dawn” offers two different and mutually defeating prologues: the survivor’s narrated setup and a dramatization of Brigham Young’s (Terence Stamp) actual testimony at a post massacre government inquiry. Instead of anchoring the film in an emotional context and a factual timeline, the dueling preambles establish that both the fictional and the historical sides of “September Dawn” will be equally unclear.

Uncomfortable with blaming and demonizing Young outright, “September Dawn” instead offers the fictional villain Bishop Jacob Samuelson (Jon Voight), a pious and vengeful community leader who has endured anti-Mormon persecution from outside the congregation and the cruel whims of the church’s own patriarchy within. Like the rest of his flock, Samuelson eyes the arriving wagon-train emigrants with contempt — and the herd of cattle and horses they bring with them with envy.

Samuelson has many wives and two favorites among his sons: Micah (Taylor Handley), himself an eager husband to multiple women, and Jonathan (Trent Ford), unmarried and uneasy under the yoke of expectation that he shoulders for his father’s religion’s sake. As they ride among the emigrants, Jonathan catches the eye of Emily Hudson (Tamara Hope), a fetching and virtuous young Irish girl. Emily and Jonathan’s attraction is not only mutual, it is instantaneous, binding, and eternal, as they proclaim to each other periodically throughout the rest of the film.

“A lot of things bother him,” Jonathan offers Emily by way of explaining his father’s constant state of disapproval, indignation, and rage. A convoluted series of flashbacks, family arguments, and clandestine meetings confirm that Jonathan may be understating things. His father’s religious, personal, and political bugaboos are apparently legion.

Within a few days, Samuelson’s right-hand man, John D. Lee (Jon Gries, Rico from “Napoleon Dynamite”and son of underrated 1960s and ’70s action director Tom Gries), has persuaded a local Paiute tribe that the settlers temporarily camped out on the meadow are an advance force bent on destroying both the American Indians and Latter Day Saints’ way of life.

Though various members of the film’s cast attempt to make some kind of storytelling order out of the script’s anachronistic, episodic chaos, they are ultimately swallowed up in a tornado of laughable dialogue and messy scene construction. Ms. Hope makes a particularly courageous effort to infuse her lifelessly written character with a spark of intelligence and passion. Unfortunately, Mr. Voight, who has, in films like “Runaway Train” and “Anaconda,” indulged in scenery chewing binges rivaling even Al Pacino’s post-Method “hoo-hah!” years, plays it straight for once, and his fist-shaking condemnations and unconvincing rabble-rousing bear little or no conviction.

On the way to the obligatory scenes of carnage the history and genre demand, “September Dawn” catalogs institutionalized Mormon hypocrisy and cruelty with such an archaic moustache-twirling simplicity that it inadvertently evokes H.B. Parkinson’s infamous and ludicrous 1922 film melodrama “Trapped by the Mormons.” Micah’s transformation into a tomahawk-wielding, blood-drooling berserker, and a midfilm depiction of a Latter Day Saint secret ritual initiation that seems to have been cribbed from a Stephen King novel, hint at a creative direction that might have made “September Dawn” more entertaining, though probably no less insulting to contemporary followers of Joseph Smith and Brigham Young.

Mr. Cain has described his best-known previous picture, 1988’s brat pack Western “Young Guns,” as “a biker film on horseback.” If the creation of “September Dawn” had been governed by similar exploitation filmmaking logic, perhaps it could have heralded a new sub-genre and been the first Mormon werewolf movie. Instead, “September Dawn” offers a brainless, clumsy, and repellent trampling of history, religion, and Western movies likely to please no one.