I would ask on www.Timbercrawler.com alot of the guys on there are from portland and would probably know some good trails
Most of them hit up TSF. TSF is not like CA trails, alot of dirt trails, muddy areas, and some mini rubicon trails. And some hit up the Reiter, Naches, and other trails in the WA area. White Trash could tell you more about those. There are some in the Bend/Prineville/Redmond area. If you like sand, there is Sandlake, Florence, and Winchester Bay dunes. Timbercrawler site is in a low right now, due to some internal politics, but once they come back, and when the snow hits, they usually hit up the Goat Mtn area for some snow wheeling, which is in your neck of the woods, Colton, OR.
Link to TSF info!
http://www.oregon.gov/ODF/TSF/Recreation.shtml
