Big skies, big adventure and big spirits: This is Montana. It’s where fertile plains collide with the Rocky Mountains and the country’s fastest land mammals run the grasslands known as the American Serengeti. It’s also where Lewis and Clark faced towering stone obstacles and Custer faced an even more daunting foe. This aerial journey showcases the Treasure State’s mountains and milestones, its legends and landmarks, all from spectacular heights. This is the fourth of seven programs from Smithsonian Channel’s epic series of the nation’s most treasured landmarks.