Hey Chuck, how bout taking the Nestucca river road west out of Yamhill. Lots of roads off into the timber off of that main road. I'm sure there are others on here that wheel around that area.
Another suggestion, Get a Metsger Map ( Bi-Mart) there are a lot of roads marked as "Jeep Trail" on those maps. You might also buy a Forest Service map too... I'm waiting for the new ones to get in stock, they are late this year.
Just have to get out and talk with some of the local 4x4 guys and see where they go in your area... Good luck ! "BH"