It's a bit of a drive from Portland, but these shuttleable Downhill/Freeride trails are the tits, even in mid-December!
I was fortunate enough to get towed into this impressive trail by the builders, and got to enjoy a fantastic mix of steeps, jumps and berms over the course of this 10-minute descent.
If you find yourself in Roseburg, be sure to hit up Canyon Creek Bicycles, and they might be kind enough to show you around.