California’s diverse geography and habitats have allowed four species of salmon to live at the southern end of their ranges: Chinook, Coho, Pink, and Chum. California Chinook occurs as eight genetically distinct populations (Evolutionary Significant Units or ESUs), seven of which are found only in California. Likewise, there are two ESUs of Coho salmon, one endemic to the state. California’s small runs of Pink and Chum salmon may actually be maintained from strays from northern populations in Oregon or Washington, but more research is needed on the origins of these fish. Perhaps the most distinctive of these salmon is Sacramento River winter-run Chinook salmon, having evolved to exploit the cold, spring-fed waters found year-round in tributaries of the upper Sacramento River.