I have been having nightmares about only having done half of the route on the big day!
The big day? Is this a wedding in Montana?

We are planning going through Vegas-Salt Lake City and trying not to wander on the way there. We will wander on the way back! So no desert... I am nearly disapointed! I really want this trip to be fun and to remember it as a big adventure.
You will certainly see desert on that route -- how much time will you have for the "wander" portion? It would be VERY EASY to take a month to make the drive from Montana to Los Angeles and still miss most of what there is to see.

Mark