The 5-cent stamp commemorating the 50th anniversary of the National Park Service was first placed on sale in Yellowstone National Park, Wyoming, on August 25, 1966. The design symbolizes the nation's three categories of parks - natural, historical, and recreational. The green angular elements suggest nature through mountains and recreation through tents. The three black dots represent cannon balls, symbolic of historic areas such as Fort McHenry, Gettysburg, and Independence Hall.
The stamp was designed by Thomas A. Geismar and printed on the Giori press. It was issued in panes of fifty and authorized for an initial printing of 117 million.
Postal Bulletin (August 4, 1966).