Awesome ride report! It's always neat to see this country from another perspective a I'm glad you got to see Des Moines, my favorite city in my home state. A fun ride is from the old capital bilding in Iowa City, to the new capital on highway 6. Northeast Iowa is the best riding in the state though but it doesn't even come close to being as cool as Oregon.
That black car you were lucky to have seen is a Chevrolet Camaro. Probably a '68. My favorite car and the inspiration for my band, The Camaro Twins.
There are some great rides in Oregon that you will love and plenty of good events so when you're closer to the area I'll try to let you know what events are going on. There's too much to see out here but Astoria is quite nice to visit if you want to see a nice town on the coast.