I need tips on my Mormon Trail trip

[_BartBurk]

We're heading out to Provo for a family gathering in August. On the way I plan on going on U.S. 20 through Chadron, Nebraska then onto Casper, Wyoming where we will be picking up part of the Oregon/Mormon trail. My current plan is to go on 220 to Muddy Gap and then head up 287 towards Lander before going south on Wyoming 28 and then 191 to Rock Springs. My only concern is what Wyoming 28 is like -- is the road really mountainous or is it flat especially through what is called "South Pass"? What is the road like?