Keywords: 21 Sep 1961 Cheyenne Mt, Interior const, rail.jpg NORAD blast doors Cheyenne Mountain Colorado USAF photo URL https //www cheyennemountain af mil PD-USGov Construction of Cheyenne Mountain Complex Tunnels in Colorado Rail transport in Colorado 1961 in Colorado September 1961 in the United States Photographs taken on 1961-09-21 |