Some local spots
Browns Camp is prolly the closest, hence most crowded.
Upper Nestucca (Trask) has some good single.
Sand Lake on the coast for beach riding is closest for sand (also crowded).
2 of the best areas in Oregon(me thinks):
China Hat (East Fort Rock) near Bend is world class. Dusty as h-e-double-hockeysticks in summer.
For sand/dunes Winchester Bay is my favorite.
$0.02
Don't forget your OHV tag.(2 years = $10.50) last I heard the fine was $250.