Book excerpt: During the 1930s San Francisco's most ambitious public murals were painted by artists on the left. In this study, Anthony Lee shows how these painters, led by Diego Rivera, sought to transform murals into a vehicle for their rejection of the economic and political status quo and their support of labor and radical ideologies, including Communism. In addressing these subjects, the mural painters developed a new imagery, based on the activities of the city's laboring population - its efforts to organize, its protests, its strikes.