The Trail of Ten Falls in Silver Falls State Park is a really nice hike, with not too much up and down but great scenery (including, yes, ten waterfalls dropping between about 27 and 178 feet). It's only about 60 miles up I-5 from Oregon. It's a 7.5-mile loop so a decent though not too long dayhike; also, there are several bailout spurs should your knees start to ache. Silver Falls is a popular park, so go midweek to avoid the crowds if you can.