Known for her documentary-esque tales of 20-somethings in transitory funks, Kelly Reichardt explores new ground in her period Western “Meek’s Cutoff,” a harrowing story that represents a substantial stylistic leap forward for the young filmmaker.

Along for the ride is Oscar-nominated actress Michelle Williams, who plays Emily, matriarch to a group of pioneers headed west in the year 1845.

Based on a real-life incident, members of an Oregon-bound wagon train are led off course into an unruly desert by their bullheaded guide, Meek, played by Bruce Greenwood. Desperate, the group trudges on. One day, they capture a stoic, non-English-speaking Native American and enlist him in hopes he’ll lead them to water—despite Meek’s claims that doing so will lead to their demise.

With Emily making this decision, the film adopts a number of contemporary political and social allusions that subvert its old-timey Western feel. As Meek preaches his manifest destiny madness, Emily represents the film’s ethical core. She forthrightly defends the group’s newfound steward, despite the fact that she has no real idea where he might be leading them.

After garnering praise for her performance in last year’s melancholic “Blue Valentine,” Williams dials back the garish overacting that plagued that film in favor of a naturalistic approach.

She’s barely recognizable underneath the pounds of soot and dirt that cover her face, but her presence amid this ensemble cast is formidable. By asserting herself as the only member of the party with the gall to stand up for something, she displays a fortitude reserved for the toughest Western heroes, effectively placing her at odds with the boastful Meek, who fancies himself a man’s man despite his ineptitude.

Beyond characterization, much of the film’s visual style revolves around capturing the rugged detail of the desert landscape. Reichardt’s largely static camera captures the peaks and valleys with the delicacy of a still image. These artful compositions elevate what are admittedly barren images into something far more substantial.

Setting has proved vital for Reichardt in the past. The wooded terrain of “Old Joy” and transient cityscape of “Wendy and Lucy” play key roles in extending Reichardt’s larger thematic ideas opposed to mere placeholders in which her characters interact.

“Meek’s Cutoff” is no exception. Despite its desolate nature, there’s an majesty to this wilderness. Its sloping hills and vast skies can accurately be described as beautiful even as the characters suffer through them. There is no psychological connection between the characters and environment they exist in. The two are wholly at odds.

As a result, the film’s breadth renders it more exhilarating than Reichardt’s previous minimalist experiments. Tensions are heightened and stakes are raised. But she isn’t afraid to underplay the severity of the situation by focusing on authenticity. The arduous and ritualistic nature of their travel magnifies the nitty-gritty of life on the prairie. Sweeping tracking shots of wooden wheels grinding against coarse dirt keep the film grounded in realism.

When moments of dread do arrive—such as a gripping Mexican standoff that finds guns drawn on Meek and Williams—they feel entirely genuine, despite operating as somewhat tawdry plot points.

Finding her footing between the genre sensibilities of John Ford and subdued tonal musings of legendary Japanese director Yasujiro Ozu, Reichardt has produced a film that is the best American release this year.