The flag of the state of Montana consists of the image of the Montana state seal centered on a blue field.
Within the seal, a plow, shovel, and pick rest in a field in front of the Great Falls of the Missouri River. The ribbon contains the state motto, "Oro y plata" (Spanish for: "Gold and silver"). The current flag was adopted in 1905, and the word "Montana" above the seal was added in 1981. In 1985, the flag was again modified to specify the font used in "Montana." Before it was adopted as a state flag, it was used by Montana troops deploying for the Spanish/American War.
small tweak to existing flag using bison skull symbol in place of state seal. by Zawsi
Oro y Plata (Silver and Gold) - the bison skull is an old and loved symbol of Montana that can be found on its license plates and state quarter. Oro y Plata is the state motto and is represented by color. by Zawsi
Clean. by Zawsi
MT Flag Proposal "apollohawkridge"
Updated proportions to a proposal by Andrew Rogers. The triangle shapes represent mountains and a stylized M. Gold and Silver colors are from the motto in the state seal, “Oro y Plata.” Blue is for the color of Montana’s “Big Sky.” Posted by Preston Knapp 
Proposal for a flag for Montana, taking the colors and the basic layout from the state seal. By Qaz Dec 2019 (details)
Proposal for a flag for Montana, taking the basic layout from the state seal. Reduced number of colors. By Qaz Dec 2019 (details)
A revision of an outstanding design by Leonardo Piccioni. Part of series of designs for state flags, all in blue and white. (Posted by Ken Morton)
41 gold circles represent the admission order number of Montana. Blue field for Big Sky.
Light blue 'big sky', sun from seal, mountains in the shape of an M, gold and silver (oro y plata) separated by dark blue to follow rules of tincture.
Sky blue for Big Sky State, sun from current flag, gold and silver stripes (oro y plata) separated by dark blue to symbolize state's water resources. White space for snow and Glacier NP.
Variations on above theme
Same as above, adding a grizzly bear print to symbolize state animal.
Results from the US State Flags contest to try and find the best redesign idea.