Check out Northeast Oregon Wheelers, they are spread out over the area. Also Deschutes County 4 Wheelers are in Bend, but might be a little far for you. W/E of Aug 3rd will be a meeting and maint. party up on Santiam Pass on Hwy 20 west of Sisters. Camping at Benson Sno-Park by Hoo DOO ski area, and a NASTY trail to run and work on.
Up by Baker City is a 4600 acre open area called Virtue Flat. Call BLM office in Baker and talk to Kevin McCoy about it. Trails from mild to wild +. Not all that far from you if you camp for a day or so and go up through Austin Jct at Hwy 26 and 7.
You will have a small open area on Little Canyon Mtn in one of the old hydraulic mining pits, but don't know if it is open for use yet or not.