Perhaps look at the bighorn mountains (go in at Kaycee... mayo worth slip road, follow road till it meets the paved road going west from Buffalo, then head west again) and Pryor mountains (feral horses... though they have DNA from the horses the Spanish brought to the Americas... some have stripes on legs)... also "big Ice Cave" ... the main road is on south and east end, and this is paved, but there is a cool rough track up the mountain coming from west... mind the rattlesnakes, especially the lower grasslands as you approach... there really can be quite a few.



If you don't mind staying east longer before turning west to go to Glacier, consider Charles M Russel NWR and American Prairie reserve north of the Missouri... bison have been reintroduced... this has low number of visitors, very remote... when it rains it may be days before you can drive again because the mud is that so bad. So, do look at precipitation forecast before going in, take enough water, food, satellite communication.


On way south, maybe visit Bison Range on Flathead Indian reservation, potential side trip on the Magruder corridor (MT ID border), head south into the bighole valley (Big Hole National Battlefield), long gravel road through centennial valley and red rock lakes...get out at west yellowstone




Have fun!