Walla Walla River salmonid populations (including tributaries). The Walla Walla River originates in the Blue Mountains at an elevation of approximately 6,250 feet. It flows north from the Blue Mountains and enters Washington State just north of Milton-Freewater, Oregon. Primary tributaries to the Walla Walla River include the Touchet River and Mill, Birch, Cottonwood, Mud, Russell, Yellowhawk, and Dry creeks. The Touchet River drains a majority of the northern portion of the Walla Walla watershed. Mill Creek and its primary tributary, Blue Creek, drain a significant area in the southern and southeastern portions of the watershed. Mill Creek begins in the forested uplands, dips south into Oregon, and returns to Washington where it passes through the City of Walla Walla.