Does Mountain Directory West have any significant notes along the most obvious route(s)? Picturing the territory in my mind, I can't think of any mountains that you have to cross. I40 coming up from the Colorado River crossing is probably the biggest grade. Flagstaff may be the highest point - or at least comparable to Durango.
Without pulling up a map I'd suggest going NE from Flagstaff past Tuba City, and then jogging a bit around 4Corners to reach Cortez, and then east to Durango. An alternative would be to stay on I40 to New Mexico (Gallup) and then north. There's a mountain range on the AZ/NM border that you have to skirt one way or other.
