I agree with the folks. I would also say weather wise, starting in Cali might be better. Summer doesn't officially start in the NW until 5 July (it honestly rains right up through 4 July and at midnight stops...honest to goodness). September in Oregon is always glorious (my favorite month of the year...sunny, dry and just warm enough, but cools down nicely at night, and very few bugs).
I love the coast, particularly the central and southern Oregon coast. The northern bit is full of Portlanders and art galleries, which is not why I go to the coast. You will definitely need reservations at the campgrounds. It is hard to fly by the seat of your pants, because this is where everyone goes when it is hot or they want to play hooky from work.
Central Oregon offers some amazing High Dessert experiences, including Lava Lands (and tubes you can hike through) as well as wonderful lakes, rivers, mountains and all sorts of outdoor activities. It tends to stay drier out there too. In a couple of weeks we are heading out to Fossil Oregon to check out a dude ranch and hopefully find some fossils. The Painted Hills are gorgeous too. Smith Rocks is famous for its rock climbing, but the hiking is also very good. It is really beautiful there too. It is just outside of Terrebonne (pronounced Terra-Bon) and Madras (we say Maa-dress...not said like the Indian dish). I hear the Oregon Caves are quite interesting as well (in southern Oregon). Haven't been yet, but hope to hit it at some point. Crater Lake is one of the most wonderful places on earth (not just saying that because I am native and partial, it really is astounding).
Eastern Oregon is amazing, and I absolutely love a small town up in the NE corner of the state called Joseph. They call it America's Switzerland (there might be a few of these), and the Wallowas are an amazing mountain range.
The gorge is lovely and you will probably be coming through during the fruit harvest. The "Fruit Loop" in Hood River is always fun and delicious. Loads of apples and pear as well as other crops. You might be on the early side, but things should be close. You can also get up to Hood easily from there.
If you want to know more about Oregon (and maybe a few things I don't know) you can check out www.traveloregon.com.
Loved the Redwoods, St Helens, Rainier National Park, the Olympics, Timberline Lodge (they do lovely lunches and dinners and is where the exterior scenes of "The Shining" were filmed...the interior is amazingly beautiful).
Not sure if that helps or makes things more complicated. Also, Oregon has really come about as a place to eat and drink. Take in some of our wineries and breweries, seafood, enjoy our produce and dairy products (Tillamook will probably be some of our most famous, and you can get it fresh at the factory right along the coast).
If you have more questions on Oregon, let me know. Have a great trip!