The Tijuana River Valley Historical Ecology Investigation synthesizes hundreds of historical maps, photographs, and texts to reconstruct the ecological, hydrological, and geomorphic conditions of the Tijuana River valley prior to major European-American landscape modification. How did the valley look and function before there was the state of California, the city of Tijuana, or an international border? What habitat types and wildlife were found there? How have these habitat types and the physical processes that shaped them changed over time? And finally, what can the valley’s ecological past tell us about its present and future? In answering these fundamental questions, this richly-illustrated study provides scientists, managers, and residents in the valley with information designed to support and inspire ongoing management and restoration activities.