In the time you have, I would stay and explore Oregon, which has much to offer.
You could drive up to Seattle, but Portland is a little gem of a city that reminds me of the Seattle I knew in the 60s. I call it a pocket metropolis. Not to be missed if you like bookstores at all is Powells, one of the best anywhere and huge. The Governor Hotel downtown is a gorgeous and historic hotel. In October, you might be able to get decent discounted rates. There are still great Oregon microbrews. One of my favorites is Widmer Hefewiezen. Another popular group are the Bridgeport Ales including Blue Heron.
The entire length of the Oregon Coast is breathtaking and makes for a very fun drive. One of my favorite places is the Netarts Peninsula. I love the small town of Oceanside. Driving there will take you past Tillamook and the creamery is a must stop. Killer cheese and ice cream!
The area along the Columbia River is spectacular. WIllamette Falls, the Columbia Gorge Hotel, etc.
You might consider a trip to Mt. Hood if the weather is holding. You don’t want to get caught in early snows. The Willamette Valley at the base of Mt. hood is one of the most gorgeous and lush I have seen. There are also some outstanding wineries in the area you might enjoy visiting.
If you do go into Washington, may I suggest Mt. St. Helens? It is not that far from Oregon and an indescribable sight that is not done justice by photos.
Astoria at the mouth of the mighty Columbia is a charming little town.
Also, should you go south, the Siskiyous, the mountains that straddle the border with Northern California are breathtaking.
Have a great trip!