Nez Pierce 1877 John Clymer

The picture has something of this: cavalry, people, mammal, seated, weapon, man, gun, group, military, soldier, herder, transportation system, skirmish, cowman, rifle, war, army, field, battlefield.
Perhaps it’s a painting of a group of men riding on the backs of horses in a field with a stream running between them and a mountain range in the background.