Salmon are iconic fishes of the North Pacific Rim. The evolution of Pacific salmon, formerly thought to be an ice age phenomenon, is now known to date back at least to the middle Miocene. In this volume nine lineages of salmons, trouts, and chars are re[prted from the late Miocene in drainages of the North Pacific in North America. The lacustrine fossil fish assemblage from the Late Miocene Chalk Hills Formation (8.7 to 6.3 Ma), southwest Idaho and southeast Oregon, exhibits the greatest salmonine diversity of any Cenozoic paleontological site known – five lineages.