In addition to all that has been suggested, I spent most of my childhood vacation time camping in the areas your trip will cover, so here are a few more suggestions:
Northern CA/southern OR: Jedediah Smith State Park near Crescent City is very accessible. Plenty of redwoods and it's easy walking. It was a favorite camping spot for us growing up. Another coastal spot that is very interesting is the Oregon Dunes National Recreation Area looks like the Sahara Desert, but there are also lakes, etc. Inland, Mt. Shasta and Mt Lassen are interesting. One can hike to the top of Mt Lassen, weather permitting--it was easy when I was 12, and even my parents who were smokers made it to the top. Lassen Park has many different sites. The volcano erupted in 1914 so there is a lot of fascinating volcanic geography in the area.
In southern Oregon there's Crater Lake, which is a short but very winding drive from Medford. It's a must see to believe place.
Ashland's Shakespeare festival is one of the best anywhere. The outdoor Tudor style Elizabethan Theater is exquisite, and it's located on the edge of Lithia Park which is a gorgeous park that starts downtown and goes up to the edge of town. The park is beautifully lit at night when you walk through after the performances. There are many bed and breakfast places in Ashland.
If you want to see a place that will make you think civilization doesn't exist, then consider driving through the Trinity Alps. The road is a bear though, and not much in the way of gas stations.
WA: Near Seattle the Ballard locks connecting Puget sound to Lake Union, and there are fish ladders where you can see the salmon jump during spawning season, mostly in June. If you do the Space Needle, lunch in the restaurant isn't outrageous, or it wasn't the last time I was there and the view changes as the restaurant rotates. Tacoma has the Museum of Glass, where you can watch artists and students make glass works of art. It's surprisingly interesting. The Olympic national park is beautiful with great hiking trails, but a bit out of the way.
You could spend a lifetime in the area and never see all of it. Good luck choosing.
Also the best weather is late summer early autumn for the coastal regions, especially up north. Often it's quite rainy in June in Washington. And there's no point in seeing the famed Oregon coast when it's fogged in.
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