Always call ahead to see what vehicles are allowed into each area.
ATV Rentals Spinreel in Oregon http://www.spinreel.com/3.html
Christmas Valley Back Country Byway, Silver Lake, OR - The byway is made up of paved and gravel roads that require high clearance vehicles. There are alternate routes for passenger cars.
Deschutes National Forest , Bend, OR - Within the forest's boundaries are six wild and scenic rivers, 157 lakes and reservoirs and nearly 1,400 miles of trails, including 60 miles of the Pacific Crest National Scenic Trail and the Newberry National Volcanic Monument.
Mount Hood National Forest, Gresham, OR
Oregon Dunes National Recreation Area, Reedsport, OR - The Oregon Dunes National Recreation Area stretches for 36 miles from Florence to North Bend. Visitors can explore its 31,500 acres on hiking trails, horseback, boat or off-road vehicle. Oregon Sand Dunes - between Reedsport and Florence; off HWY 101
Siuslaw National Forest, Corvallis, OR - There are trails suitable for mountain biking, horseback riding and off-road vehicles.
Please send me suggestions.