Here's a fun loop just outside of Portland I did earlier this fall. A quick and easy trip you can get done in an afternoon. You know, and nice mix of pavement, trees, and dirt for the busy biker on the go. It primarily follows Lolo Pass up over the West side of Mt. Hood, but with two variations I found to be worth the detour. And I suppose by the time most folks read this post it'll be too late to get this ride in due to snowfall, but hey at least you can start planning for spring!
I assume a lot of folks in the Portland area already know about Lolo Pass. There were certainly no shortage of dual sport riders on the road when I was out. The easiest way to access it is by hanging a left in the town of Zigzag heading Northbound on Lolo Pass Road (NF-18). But if I may make a small suggestion... Just out of Gresham you can link up a couple of back roads and get onto SE Marmot which is sort of the back way into Lolo Pass Road. It takes you down into a really beautiful valley bordering the Sandy River with some impressive views of the West Side of Mt Hood.
The second variation is a few miles up E Lolo Pass Road, just as things start to get a little steeper there's a fork onto Muddy Fork Road:
I definitely recommend this route over taking Lolo Pass Road the whole way. It's far more scenic, a bit more challenging riding, and gets you up onto the dirt a lot sooner. It's primarily a less traveled road over broken asphalt. I like it as cuts up through the forest rather than under the power lines of Lolo Pass. Right at the summit there are a number of dirt roads worth heading off onto for a little exploring before dropping down into Hood River.
Again this is definitely more of a summer ride, but it gives you all winter to think about how good that beer stop in Hood River is gonna taste when it's warm and sunny next year.