The single most splendid one day ride I've enjoyed while touring in the US is Going to the Sun Road across Logan Pass in Glacier National Park, Montana. I went west to east, and am not sure if the experience would be the same in the other direction due to some unusual aspects of the road and topography. I benefited from perfect weather there.
I would also make sure you see some virgin redwood groves in far northern California. I recall that Jedediah Smith State Park had some impressive groves. There is nothing like an old growth redwood forest.
If you find yourself crossing northern Vermont, the Haskell Free Library & Opera House built literally on top of the Canada-US border at Derby Line, VT, & Stanstead, PQ, is absolutely worth a visit. See: