I believe "Going West" is a painting to be based on drawing benton did while traveling across the united states his second time. Vast fields and endless sky gave him a sense of immensity of the landscape, and insignificance of an individual. He saw the train as a powerful machine that allowed us to traverse the vastness of the west. While he was traveling Benton did many drawing and quick studies. The detail in the painting is scant because he probably didn't have tim to explore the detail. This layout appears in a few of his other works including "America Today."
Timing of Going West within Thomas Hart Benton's career.