You might want to get an Atlas and Gazatteer for a couple of states. We have used our Colorado one until the pages have fallen out. They show everything including many forest roads. I like them because they show mnt. passes and elevation. I think I-25 into Wyoming fairly far north and then west. We have friends who live in Sheridan, WY and they went to Yellowstone from there. I don't know all the WY interstate roads, but I think their route was pretty straightforward, pretty much due west.
Where in Littleton? We live close by. Welcome, by the way. This is the place to find all things AS!!
Leigh (IB Aluminated)
"When a great ship is in harbour and moored, it is safe, there can be no doubt. But that is not what great ships are built for." by Clarissa Pinkola-Estes, author of ‘Women Who Run With the Wolves’