It took some time for planners to coalesce around the theme of progress, which is surprising since it is the common theme of almost all expositions. As the first exposition celebrated the completion of the Panama Canal, the second would celebrate the completion of the Metropolitan Water District Aqueduct from the Colorado River and other federal projects. Overriding other displays in importance were those showing the taming of the Colorado and Columbia Rivers. Subsidiary to these, models of the Metropolitan Water District Aqueduct, the Grand Coulee, Boulder and Parker Dams, the All-American Canal, the San Francisco and Golden Gate Bridges, and the improved harbors of Los Angeles, Long Beach and San Diego proclaimed the millennium had arrived.

Exhibitors showed many models of the same projects in the Palace of Water and Transportation, the Palace of Electricity and Varied Industries, the Palace of Education, the Federal, and the California State Buildings. Even after it had been repeated in almost every building in the Palisades, a concessionaire set up a model of Boulder Dam in the amusement section of the Exposition.