The Walla Walla Watershed is located in southeastern Washington State in Walla Walla and Columbia counties, extending into northeastern Oregon. This drainage basin covers approximately 1,760 square miles, two-thirds of which are within Washington. The Walla Walla River starts in Oregon, flows north into Walla Walla County, and drains into the Columbia River. Major tributaries to the Walla Walla River include the Touchet River, Dry Creek, Pine Creek, and Mill Creek.
To learn more, check out these websites, including their maps:
US EPA Walla Walla Watershed Profile
Washington Department of Ecology Walla Walla Watershed maps
Explore your watershed (instructions for setting up a detailed watershed map using Google Earth)