Earlier quoted context omitted.
It's likely that, being 30 years old, it was outdated and replaced by a newer secret structure anyway.
I would actually doubt that, myself. The costs of building those structures were enormous, and by 1970 or so hydrogen bombs had become powerful enough and ICBMs accurate enough that it was pretty much impossible to build something that would survive a direct hit. Once that point is reached the only protection that the site has is its secrecy, and it costs the enemy less to hire spies and launch satellites than it doe…
The Soviets had versions of the their enormous SS-18/R-36 missile with a single 25Mt warhead - these were presumably aimed at hardened sites like NORAD and Raven Rock:
http://en.wikipedia.org/wiki/R-36_%28missile%29
The thriller "Arc Light" has scenes describing what would have happened to Cheyenne Mountain if it had been hit by multiple SS-18s: