There were 6 Titan I ICBM Missile sites in Colorado. They were installed in the early 1960's by President Kennedy to counter the cold war threat of a 'strike first' assault on the U.S. And it was a good thing that he did it, for if it were not for this capability, the Cuba Missile Crisis would have ended very differently. It's a shame that we needed our own 'strike firs' nuclear offensive, but it was the only thing that made Khrushchev back down.
If you look to the North you will see two grain silos barely visible on the horizon. They sit right at the heart of Missile Silo Base 724-B. Every other a day, a truck carrying between 3 and 4 servicemen would pull up to the 16" concrete reinforced door to re-leave the previous crew and start a 72 hour watch of their own. The compound consisted of 3 missile launch silos, a service entrance and a maintenance elevator shaft, and two exhaust ports for the buil-in diesel generators that would power the installation in case of a real emergency. The control room was built 6 stories beneath the surface which rendered it invulnerable to a direct nuclear blast. They were under the direction of NORAD Cheyenne Mountain which would have directed them to launch based on a command by the President.
Fortunately these missiles were never need, but their presence and capability deterred the soviets from attempting a nuclear strike in a mistaken belief that they could win a nuclear war with the U.S. These bases were eventually De-comissioned and replaced by a more capable Titan II ICBM system. They have been de-comissioned now as well.