 East of the Continental Divide in Alberta and Montana, westslope cutthroat trout are native to the upper Missouri, Milk and North Saskatchewan rivers, but not the Yellowstone River to the south.In Montana, the historic range extended east to the mouth of the Judith River and south into the Madison, Gallatin and Jefferson river systems.Isolated populations of westslope cutthroat trout exist in upper tributaries of the John Day River in the Strawberry Mountains of Oregon and Columbia River tributaries along the eastern side of the Cascade range in Washington.