The collection consists of stamped First Day of Issue envelopes spanning the years 1933 to 1952. During this time Joseph C. O’Mahoney served as First Assistant United States Postmaster General and later as U.S. Senator from Wyoming. Each envelope is addressed to a Cheyenne resident, P.J. Gauff, and bears a special cancellation applied on the First Day of Issue in the city where the stamp was issued

Ninety of the envelopes are accompanied by letters from O’Mahoney explaining the background behind the stamp. President Franklin D. Roosevelt, a stamp collector, was directly involved in the design process for some of the stamps

O’Mahoney served under Postmaster General James A. Farley, a New York political ally of the President. Farley autographed one of the items in the collection, a 1934 envelope with a stamp depicting the Old Faithful Geyser, and postmarked Yellowstone National Park, Wyoming

When Senator John B. Kendrick died in office in 1933, Governor Leslie Miller appointed O’Mahoney to complete the unexpired term. He would continue in the office until defeated by Frank Barrett in 1952. He was elected again in 1954 and served an additional Senate term

The collection also includes a First Day of Issue commemorative brochure for the 1993 Oregon Trail stamp, with stamp attached