You can buy a Oregon Recreation map at any Fred Meyer or Bi-Mart store... They have the OHV listings. also stop at a local ranger station and get up to date maps of your area. Lots use GPS devises, I'm old, I like MAPS...Also grab a BLM map from the local BLM office.
Try to "network" with others in the area, they can help lead you around to the places to play... Good luck ! "BH"

 

This website has a pretty good list of OHV areas in OR: OHV Areas

 

Off the top of my head there's Virtue Flats. Then there are the trails in Morrow County, but they're closed for the winter. Finally, there's Mt. Emily.

For a complete list of trails:
http://atv.prd.state.or.us/places.php

 

You guys are all great! Thanks for all the info.