The first headquarters of the North American Defense Command at Ent Air Force Base, Colorado Springs, Colo. Ent opened in 1951 and closed in 1976. The site is currently home the U.S. Olympics Training Center. NORAD has since been renamed the North American Aerospace Defense Command. 

Courtesy NORAD

One of the most enduring symbols of the Cold War turns 60 Saturday. It’s the North American Aerospace Defense Command, or NORAD. It's a massive man-made bunker built deep into Cheyenne Mountain west of Colorado Springs. Inside, workers monitor the skies in case of nuclear attack.

Run jointly by the United States and Canada, NORAD was initially located at Ent Air Force Base in Colorado Springs. Author Garrett Graff tells Colorado Matters about NORAD's history, a terrifying false alarm that sent fighter jets scrambling, and the facility's relevance today.

Graff wrote "Raven Rock: The Story Of the U.S. Government's Secret Plan To Save Itself — While The Rest Of Us Die."