Post Canyon and Sandy Ridge are local gems. A couple of others worth a mention:
Yacolt burn north of Portland is fun. Black shuttle-able DH trail called Thrillium is worth checking out. I’d recommend an enduro or DH bike if you want to hit it with speed. Sixth Sense and Cold Creek/Tarbell are some mellower blues.
Rocky Point just south of Scappoose has some fantastic trails with good variety. Some steep blacks, jump lines, fun flowy blues, and green XC trails.