“Rockies might be a bit tough.”
You just follow the route laid out by the surveyors of the first transcontinental railroad. Those men did an amazing job finding the lowest way through the Rockies. I’ve read that you cannot find a better route than what they laid out.
Great interactive map lets you see the proposed route in detail:
https://gis.railstotrails.org/grtamerican/
Remember, Lewis and Clark pushed wagons and carts over these mountains in far more difficult circumstances. And they didn’t have carbon fiber or a c-store every 10 miles.