In Ilisa Barbash and Lucien Castaing-Taylor's unforgettable sheep-herding documentary, the breathtaking vistas of big-sky country come close to heaven. But it's telling that AC/DC's "Highway to Hell" can be faintly heard over the sound of the electronic contraptions that hired hands use to shear the docile creatures during one of the roundup's preparatory stages. Sweetgrass captures the arduousness and the awe (not awww) of a vanishing way of life. Animals strike curious poses: One of the white, fluffy sheep stares right into Castaing-Taylor's camera as the film begins, a moment played not for critter cuteness but for ovine empathy, immediately setting the patient, unsentimental, observational tone. Just as you begin to distinguish the sounds of different bleats, you witness the absurd force of the sheep en masse as they run past a Radio Shack on a small-town street. High up in the mountains, they become unwieldy, leading enraged herder Pat Connolly to string together the most inspired blue streak ever uttered against ewes. Sweetgrass reminds us of the stupefying magnificence of the setting while never letting us forget the formidable perils.