Interesting regional map, showing the Dakotas as a single territory. Early counties and townships are shown, along with a number of Indian Reservations, rivers, mountains, lakes, towns, etc. One of the earliest obtainable separate maps of the territory. An excellent large format map of the period from one of the major American map publishers of the 1870s.
O. W. Gray was a publishing firm based in Philadelphia. Later, they published as O. W. Gray & Son. They published atlases in the late nineteenth century. Gray's National Atlas was one of the most successful commercial ventures of the 1870s and one of the last to employ hand coloring on maps.