This article tells the story of artist Todd Gilens' "Endangered Species" project, where four municipal buses in San Francisco were each wrapped with a photograph of a different animal in danger of extinction: a Mission Blue Butterfly; a Salt Marsh Harvest Mouse; a Brown Pelican; and a Pacific Coho Salmon. Besides alerting passersby to environmental degradation, this art project, which ran throughout 2011, reverses the customary tactics of outdoor advertising. Outdoor ads promote products and block our sense of place. By contrast, wrapping images of California's troubled animal habitats on moving buses promotes a complex environmental and historical message: the urban development all around us sits atop what had been the original skin of the earth. In telling the story of the animal-wrapped buses within the greater history of outdoor advertising and mass transit, I connect the fates of endangered natural ecosystems with their cultural counterparts such as the city's bus system.