How does Lanford Wilson use imagery in The Mound Builders?

As the curtain rises on The Mound Builders, August Howe is in his study in Urbana, Illinois, dictating notes into a tape recorder as he looks at slides of "the wreckage of last summer's expedition." The slides are projected onto a wall on the stage so the audience can see them, and the first series includes pictures of the lake, the house, the construction of the dam, the bulldozer, and the dig itself. Although most of the action of the play happens in Blue Shoals, Illinois, the Blue Shoals scenes are flashbacks, and the present time is February in Urbana. Twelve times throughout the play, scenes of August in his study are interspersed with scenes of the characters living out the events recorded in August's notes and Cynthia's slides.