“Meek for me embodies the most rugged individualism of that American type,” said Jonathan Raymond, a writer of the HBO mini-series “Mildred Pierce,” who wrote the screenplay for “Meek’s Cutoff,” Ms. Reichardt’s first ensemble drama, in close collaboration with her. “I think of the others as more middle class in their dispositions, more good citizens on some level, but he’s a real mystic wanderer.”

Meek (played by Bruce Greenwood) is the grizzled guide to the stolid Tetherows (Michelle Williams and Will Patton), the anxious young Gatelys (Zoe Kazan and Paul Dano) and the beleaguered, biblically inclined Whites (Shirley Henderson and Neal Huff, with Tommy Nelson as their child). “There was a quote I remembered that I had liked when I was 18 or something, that popped into my head: ‘I’ll go where my own nature would be leading,’ ” Ms. Williams said of her character, Emily Tetherow. The verse, by Emily Brontë, which continues, “It vexes me to choose another guide,” proves peculiarly apt for Mrs. Tetherow, who emerges as Meek’s prime skeptic and becomes an unusually vocal opponent. The actual diaries of women migrating West were also a source of inspiration for Ms. Williams. She said she marveled at the effort spent on writing at “the end of the longest day you could imagine.”

The forbearance and point of view in the journals comes out in Ms. Reichardt’s shading of events through the women’s perspective. Besides the constant visual metaphor of the obscuring bonnets, there are the intervening moments devoted to their chores (laundry, grinding coffee) and wide shots from their point of view that suggest their exclusion from major decision making, like when Meek and the men consult upon arriving at a lake that proves unpotable. But it’s also Mrs. Tetherow who first spies an Indian (Rod Rondeaux) who becomes another competing voice of authority as they drift along in increasing distress and disagreement.

Indeterminacy has become a constant in Ms. Reichardt’s films, most recently in the wanderings of the character Wendy (also played by Ms. Williams) in “Wendy & Lucy” and before that the reunion hike by two erstwhile buddies in “Old Joy.” (Both films also unfold in Oregon.) “Meek’s Cutoff” announces the theme early with a shot of a character carving the word “Lost” into a log, one of many details plucked from history. The ambiguity extends to the leadership of Meek, whose motives are questioned in the film as they were in real life.

“In a way Meek is living in a fantasy he’s created for himself about his abilities as a frontiersman, his acumen as a guide, his sixth sense,” said Mr. Greenwood, who in the film sports a rambling beard worthy of the real Meek.