Aaron Copland declared Thomson's score for The Plow That Broke the Plains to be "a lesson in how to treat Americana," and this music strongly influenced such later Copland American pieces as Rodeo and Appalachian Spring. The music originated on the soundtrack of a short Pare Lorentz documentary commissioned by the U.S. Department of Agriculture's Farm Security Administration. It's a curious film, honest in its depiction of the devastation wrought upon America's farmland during the Dustbowl years, but concluding with a call for confidence in the government's efforts to reclaim the land for future agricultural use. Thomson's music closely follows the tone of each scene, incorporating at one point a bluesy jazz band sound and at another some orchestrated cowboy tunes, all amid a more standard "classical" orchestral approach. The concert suite Thomson prepared in 1942 does not substantially differ from the music heard in the film. The bleak Prelude opposes a mildly dissonant string motif with a woodwind setting of the "Doxology"; the use of this chorale may remind some listeners of Thomson's Symphony on a Hymn Tune. "Pastorale (Grass)" is a sweet little movement employing the woodwinds (and later, brass and strings) in canonic polyphony that builds to a substantial climax. "Cattle" employs guitar and woodwinds and later, strings and brass, in a deft medley of cowboy waltzes, primarily "I Ride an Old Paint" with splashes of "Streets of Laredo" and "Git Along Little Dogies." "Blues (Speculation)" takes on alto and tenor saxophones and banjo for a 1920s-style jazz lament more comic-acerbic than pathetic. The main tune shares a subtle kinship with the Prelude's third theme. "Drought" is a haunting 16-bar canon, followed by the concluding movement "Devastation." This returns to the motif that opened the suite, touches again on the "Doxology," and then reworks the Prelude's third theme into a new, gradually more confident melody. Incongruously, a tango beat arrives, as if this were a film about the struggles of Latin American farm workers, but this helps build the music to a defiant climax in the face of natural disaster.

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