t can't be Malmstrom Air Force Base. ENT -- specifically, "Desert Crossing," "Carbon Creek," and "In A Mirror, Darkly, Part I" -- established that the Vulcans landed in Bozeman, Montana, and the Vulcans landed in the same town in which was the silo. Bozeman is in Gallatin County; Malmstrom AFB is in Cascade County. The U.S.A.F. must have built a new facility in the years between the present and the start of World War III.
A few problems with it being Bozeman, Montana. The movie take place on April 4 - 5, 2063. Bozeman is in the rocky mountains at 4,800 feet, Malmstrom AFB is on the Montana plains at 3,300 feet, if the missile complex were in Bozeman, than the area would be completely covered in snow.
Also, Data clearly states that the missile complex was located "In Central Montana.
" which describes Malmstrom AFB nicely. Bozeman is in the south-western portion of the state.
Also the START treaty has lead to the early retirement of the LGM-118 Peacekeeper ICBM, the USAF is dumping a ton of money into the refurbishing of the Minuteman Threes (they're getting the Peacekeeper's warheads), the MM3's have existing silos at Malmstrom AFB.. The plan is to keep them for "many more decades." The missile in the movie is modeled on the MM3, a new generation of ICBM's is unlikely to look exactly like a MM3. The silo has to be part of Malmstrom AFB.
Rather than conjecturing a new missile complex, it might be easier to believe in the establishment of a new community in central Montana named "Bozeman." Perhaps the former Bozeman was destroyed in the war because of the rumor that a new missile complex was being built there!