The Pacific Coast isn't a bad ride. Start up north in Port Angeles and then head south through Olympic National Park. Yeah it's peak season but you can easily get away from the hordes on a bike. That'll get some of your gravel riding done. There is some nice country inland as well, like up the Columbia River and over past Mt Hood. Some of the forest roads are awesome, as is riding through redwoods. The hiker-biker campsites in State Parks are pretty good too, $5 per person and no need to book.