Traders, agents and officers had surplus account-book paper. Plains artists had a narrative tradition that had run on hide for generations. What came out of that collision is ledger art: horizontal processions of mounted men, drawn in hard outline and filled flat, sitting directly on printed money columns.
The grid never gets painted over. Blue horizontal rules and red column rules run straight through horse and rider, and the drawing is composed against them. Colour arrives at pencil and crayon saturation because that is what the box held — nothing here was ever meant to look like paint.