From Eugene head east about 30-45 minutes for the Three Sisters National Park area. Lots of nice falls and other scenic's to see.
Or, head south about 150 miles to Mills Falls recreational area and take some of the fun hiking trails. Some large falls are easily photographed there. I'll attach a few. Try to keep in mind that Oregon probably had more waterfalls than anywhere else.. so you'll find them everywhere. Mills Falls is special though.