Oregon is 98,466 square miles, which is a little bit larger than the entire United Kingdom. That’s a lot of area to cover. If you’re ready to visit the less well-known nooks and crannies of the state, start here. Cascade-Siskiyou National Monument Cascade-Siskiyou National Monument sits at the convergence of three mountain ranges: The Cascade, Klamath and Siskiyou. The exciting geology leads .