In November of 1889, four new states were admitted to the Union—North Dakota, South Dakota, Montana, and Washington. A 3-cent rose violet stamp issued on November 2, 1939, commemorates the 50th anniversary of their statehoods.
The stamp's design shows a map of the northwestern United States with the four new states in outline. Three of the four states border Canada, and the United States—Canada border in that area follows a line of latitude that is properly shown as a curve on the map. The appearance of the states 'hanging' from this boundary like laundry items has led to the stamp being called the 'wash line stamp'.