Ive done San Anton to Seattle several times

Spots I like:

Try this on google maps

1. Roswell, NM UFO museums then due north Big empty road and easy ride to Interstate. head west.
2. Happy Jack, Az- Meteor Crater spectacular and museum, a little out of the way but worth it. Painted Desert and petrified forest are near by.
3. Monument Valley, Ut spectacular you'll never forget it Indian Reservation
4. Moab, Ut Arches National Park, spectacular too
5. First interstate west and then state highway to Scipio, Ut. Easiest and prettiest ride

Then Salt Lake City and through the Columbia River Gorge and that's the best and easiest, no switchbacks and mountains

Enjoy