The Emeryville Shellmound, on the east shore of San Francisco Bay, was excavated and subsequently destroyed in the early twentieth century. From its stratified deposits, which span the period 2600 to 700 years ago, the author identified 2,004 fish and 15,893 mammal specimens, and analyzed these and 2,302 avian remains previously identified by Hildegarde Howard in the 1920s. A battery of independent tests derived from foraging theory supports the conclusion that human-induced impacts on vertebrate populations caused declines in the efficiency of foraging across the time that the Emeryville locality was occupied.