On the center panel across the top of the north wall are figures representing the Native American and the Black races holding iron ore and coal, respectively; below are the geological strata from which these materials are mined. In these figures, Rivera preferred to develop generalized, androgynous images of individual people to maintain spontaneity in his approach to painting rather than relying on figural types. The models for the Native American and the Asian races are not known. The features of the White race were based on those of Rivera's assistant Lucienne Bloch and those of the Black on Rivera's maid, Sarah, at the Wardell Hotel. The Wardell (now the Park Shelton Hotel), located across the street from the museum, was Rivera's home during the project.

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