A perfect time to enjoy Oregon's many state parks is during State Parks Day, June 2. During this event Oregon State Parks have no day-use fee and also offer one night of free camping. While many of the reservations for this year's campsites are taken, booking now for next year isn't a bad idea.
If you are in Oregon, you can find a state park in the area you are going to be visiting here. If nothing else the free day pass is worth the trip to many of the local parks.
In addition, the day offers everything from the Governor dedicating a new trail at Willamette Park in Portland, to hay rides and hot dog barbeques in the Logging Museum at the Valley of the Rogue State Park.
Be careful though, once you get a taste of Oregon State Parks, you may not want to leave!