Final answer:
The largest city at the confluence of the Columbia and Willamette River, known as both the City of Roses and City of Bridges, is Portland, Oregon.
Step-by-step explanation:
The state's largest city that is positioned at the confluence of the Columbia and Willamette River, known as Portland, is in Oregon. Often referred to by nicknames such as the City of Roses and the City of Bridges, Portland is recognized for its vibrant community and cultural significance, including its sizeable Native American population and related organizations and services.
This city is not only a hub for commerce and culture but also for its historical importance as part of the expansive Oregon Territory, which once included present-day Oregon, Washington, Idaho, and parts of British Columbia.