The north and south walls are devoted to three themes: 1) the representation of the races that shape North American culture and make up its work force, 2) the automobile industry, and 3) other industries of Detroit (medical, pharmaceutical, and chemical). Figures representing four races hold raw materials that Rivera saw as analogous to each. Between each pair of figures, gigantic hands grasp materials used in the production of steel, symbolizing both mining in particular and the aggressive drive to capture the riches of the earth in general. At the very bottom of the north and south walls are small panels that depict scenes of a day in the life of the workers.

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