“Map of Oregon, Washington, Idaho, and part of Montana.” Philadelphia: S. Augustus Mitchell, Jr., 1864. 10 3/4 x 13 3/8. Lithograph. Original hand color. Very good condition.
In 1864, Montana was created out of the northeastern part of Idaho. Mitchell updated his map of the American Northwest to show this change, producing this version that same year. The southern border between Montana and what would become Wyoming was in flux and the border shown here disappeared soon, if it ever was an official border.