Montana has only one HMA, and it is the most famous and most-studied one, Pryor Mountains HMA.
Ginger Kathrens' "Cloud, Wild Stallion of the Rockies" series of videos shown by PBS, has probably turned more people on to mustangs than any other single influence. 

CLoud the Stallion DVD.jpg

Pryor Mountain Horse Photos:

Kelly & Lance Landry with Horse
Arrow and Image
Pryor Mtn mare
Pryor Mtn Colt
Pryor Mtn colt
Pryor Mtn Horse Range