A lot of base expansion.
And all the eggs in one basket makes it a lot easier to break all the eggs at once with one warhead.
Nor does that do anything about the co-located missile wing.
Most bases are leftovers from WWII. They are the financial lifeline to the nearby town. Congresscritters from rural areas hate it when DoD shuts down a base and deprives their state with large amounts of jobs and money.
See
Which was essentially a political suicide pact that Congress has repeated 5 times in an effort to shut down groups of unneeded facilities without each individual affected Congresscritter’s special pleading pecking the closure list to death.
If you tried going west to Mt. Rushmore, I could see it taking 11 hours, but going directly south (with just a nudge to the west after Rapid City, Mt. Rushmore is a bit less than 7 hours away. 
Going west for 10 1/2 hours will take one to Glacier Nat’l Park–well worth the drive.