According to Oregon Fall Foliage, the most color in the state can be seen in mid to late October.

There is a magical place in the Pacific Northwest where you can wander the backroads and take in the amazing changing colors of the leaves. Oregon is that place, and this state offers a number of great destinations you can choose from to enjoy the glorious scenery as we transition from the hot dog days of summer to the upcoming chill of Old Man Winter.
First, where to go and how to prepare. There is an excellent seasonal website known as Oregon Fall Foliage that will keep you updated this time of year with frequent reports on the best locations to visit and, more importantly, when. It is maintained by a local tourism bureau in the state, and relies upon observations from “forest rangers, biologists and leaf peepers” to help keep information timely.
Ideally, according to Oregon Fall Foliage, the most color in the state can be seen in mid to late October. This varies somewhat region by region though, depending upon such factors as “location, elevation and weather.” No matter the case though, you are guaranteed a wonderful drive on the many byways and backroads as you view the scenic conditions undergoing their golden transformation.

Depending upon where you drive you may, as well, get the chance to partake in fall festivals and harvests. This time of year is pumpkins galore around Oregon, and a lot of farms have events going on to celebrate not only crops like this but also apples and other produce goodness. You could, for example, make a day out of driving a farm loop, stopping at farms along the way to pick up munchies for later parking under some changing trees to frolic in the leaves.
So, intrepid backroaders, go forth in your cars, motorcycles and bikes to explore Oregon’s wandering lanes of fall foliage goodness and remember this: It is not the destination, but the journey that matters.