This are Crow Indians, traveling as a war party. The Indian in the left foreground is carrying a very elaborate otter hide bow case (otter fur was very popular for this use). The challenge in the painting proved to be composition because the dominant figures in the river are going directly away from the viewer. It was necessary to bring the viewer’s attention back into the picture by having the Indian on the opposite bank turn back to look in the viewer’s direction.
As for the mood, it is created by the interplay of light and shadow, the mix of woods and water and the romance of the West the way it was so many years ago.