David Sullivan with (from left) Gavin Mathews, Zoë Wagner and Delilah Wagner in ‘The Big Bend.’

Onion Creek Productions/Wagnervision

To say that The Big Bend is set in the American desert is technically true but also a wild understatement. The stark and unsettling beauty of West Texas, with its cliffs and canyons and ghost towns, isn’t mere backdrop to this well-observed drama; it infuses the movie on a molecular level. Brett Wagner’s atmospheric feature — which has begun its theatrical journey a couple of years after playing the fest circuit — revolves around a holiday get-together that proves anything but relaxing for two couples and their school-age kids. With its mixture of laid-back intimacy and stressed-out intensity, the story pushes the characters out of their not-so-comfortable comfort zones and into an uncharted territory that’s variously tantalizing, terrifying and forgiving.

The pull of mystery and adventure is there from the get-go, in the traveling shot that opens the film: a view through the windshield of a car moving down a two-lane highway. The travelers are married New Jerseyites Cory (Jason Butler Harner, of Ozark) and Melanie (Virginia Kull, Imperfections), in a rented SUV with their girls (Zoë Wagner and Delilah Wagner, the helmer’s daughters).

They’re on their way to visit friends who have renovated an adobe on 20 acres of cactus and scrub. The expanse of the Lone Star state that unwinds before them (a region that figures significantly in the final stretches of the Lily Gladstone indie The Unknown Country) suggests a permeable border between the alluring and the precarious, a collision of dreamscape and the everyday that’s a defining quality of Wagner’s film.

Stopping to admire the Marfa Mystery Lights, Cory gazes into the rural night with a particular ache that will color nearly all his interactions, for reasons that are gradually revealed. Although there’s tension between Cory and Melanie over his determination to keep a certain “situation” secret from their friends, there’s also a deep bond, a playful ease and a still-strong sexual attraction — a clear contrast with the strain between their hosts, the impulsive Mac (David Sullivan, who starred in the 2004 Sundance hit Primer) and the disillusioned Georgia (Erica Ash, of Survivor’s Remorse), who’s given to a thousand-yard stare as she vapes weed in their outdoor tub while he masturbates to porn in the bathroom.

Long before a visit to the national park turns disastrous, the four actors are superb at conveying the connections and rifts among their characters, and the ways this reunion will not be a simple vacation. The groaning water heater that Mac intends to repair adds an ominous bass note to the sense of looming calamity.

Friends since college, Mac and Cory are kept at arm’s length by Cory’s heavy secret. In that backyard tub and, later, enjoying a mud bath by the river, the two women are more open with each other, although Georgia does most of the unloading. Melanie, who appears to be in the early months of pregnancy, responds to her friend’s inquiring gaze with a denial that leaves Georgia unconvinced but not about to push it.

Mac and Georgia’s sons (played by brothers Gavin Mathews and Grae Mathews) are about the same ages as the visiting girls, and the kids quickly establish a rapport. But the younger girl, Fiona (Delilah Wagner), has a tendency to wander off — onto the moonlit porch to peer into the outspread desert, or, later, into the welcoming sphere of exceptionally amenable wild horses. With a creative purposefulness that artists in nearby Marfa would admire, she constructs a kind of Rube Goldberg water sculpture. And when she discovers a mud-encrusted toad, she alone is certain that it isn’t dead, making its resuscitation her project.

Fiona’s open curiosity, decisiveness and connection to nature are key to events that drive the movie’s second half, and they feel at times over-romanticized for plot purposes. The writer-director and editor Katie Ennis intercut the families’ stories with the progress across the striking landscape of an escaped prisoner (Nick Masciangelo) whose path, by boat and then dune buggy, ultimately crosses that of the wandering Fiona.

What drives the movie isn’t this action contrivance, though it’s nicely played by Masciangelo and the young Wagner and reveals the drama’s underlying optimism (embodied, too, in the yearning Americana of the score by Alejandro Rose-Garcia and Julian Cassia). The beating heart of The Big Bend is something more amorphous, the emotional pressures that each of the couples are facing, and how their time together in this rugged terrain pushes them to the surface.

The arresting landscape is alive in the elegant widescreen camerawork by cinematographer Paul Atkins (who has worked on a number of nature documentaries as well as serving as second unit DP on The Revenant and To the Wonder), which captures not just the rocky outcrops and wind-strewn detritus but the overwhelming mood of isolation in a place where streetlights and sidewalks are nonexistent and Wi-Fi signals are iffy.

If there’s a comic edge, late in the proceedings, to the declaration by older boy Connor (Grae Mathews) that “the grown-ups are thinking,” the sarcasm is earned. On the same night that the two dads make one of the worst mistakes a parent can make, the two moms have been getting wasted on tequila. Snapping to attention to deal with a waking nightmare, everyone must do their best not to fall apart.

A few plot-mechanics stumbles aside, writer-director Wagner and his nimble quartet make these characters’ collective misadventure, with its painful revelations and unlikely heroics, ring true. The circumstances are extreme and also, finally, recognizable. As Cory insists, in his genial way, “You don’t have to know a road” before you set out to drive it.