Grinnell Point, Glacier National Park, Montana; photo by Mark Stevens on Flickr (noncommercial use permitted with attribution / share alike).
The Treasure State
The most familiar nickname for Montana is "The Treasure State" because of its rich mineral reserves. All State Nicknames
The mountains of Montana have yielded fortunes in gold and silver since the first substantial deposits were discovered in the mid 1800's (Montana's state motto is "Oro y Plata" - Spanish for "gold and silver"). Montana also has sapphires (gemstone symbol of Montana).
Big Sky Country
Another nickname for Montana is "Big Sky Country," made popular by a Montana State Highway Department promotion in the 1960's (originating from a book by Alfred Bertram Guthrie Jr. titled "Big Sky").
Source
