bike the mckenzie river trail. it is east of eugene 45 min. 27 miles, 2500 ft elevation loss, oldgrowth, trailside hotsprings, waterfalls, technical lava for a few miles, fast winding singletrack. if you are going to smith, you will basically drive right past it on your way back to I5 headed south. only trouble is you need to shuttle it, but I have never had a problem hitchhiking back to the top. McKenzie R Trail is consistently rate in the top 5 best bike trails in the world.
This time of year, Lost Rocks on the redwood coast is real nice too.