NCAA Football: Georgia State at Air Force

One day after Boise State and San Diego State informed the Mountain West that they intend to stay in the conference, Air Force and Colorado State have done the same, sources confirmed to CBS Sports' Matt Norlander. The four schools had been targeted by the AAC as possible expansion candidates after three AAC teams -- Cincinnati, Houston and UCF -- announced their move to the Big 12 in September

On Friday afternoon, the Mountain West Board of Directors confirmed the commitment of its conference members. 

"The trailblazing Western institutions of higher education in the Mountain West Conference are proud of our academic excellence, the strength of our athletics programs and the splendor of our campuses, and today we are announcing our collective commitment to membership in the Mountain West," the statement read. "The success and positive trajectories of our respective members have created opportunities for many of our universities, yet we collectively believe in the strength and shared spirit of the Mountain West and in the future possibilities for our Conference. Close collaboration will continue as we identify the best path forward for the Mountain West within the evolving landscape of intercollegiate athletics."

Boise State intends to stay in the Mountain West with the hopes of a bigger invitation -- specifically from the Big 12 or Pac-12 -- coming in the not-too-distant future, sources tell CBS Sports' Dennis Dodd. San Diego State remains in lockstep with its desire to wait for a better offer rather than potentially moving conferences twice in a short period of time.

Air Force and Colorado State remaining with the league is a bit more surprising as Air Force was motivated to link up with Navy.The Rams have local interests that align with the Falcons as the universities are less than 150 miles from one another in Colorado.

However, amid forceful internal pushback, Air Force and Colorado State ultimately became uncomfortable with leaving the Mountain West for the AAC on their own rather than alongside Boise State and San Diego State, sources told Norlander.

"The American Athletic Conference has not offered membership to any institution," said AAC commissioner Mike Aresco in a statement. "Our process for considering potential members remains deliberate, strategic and focused on the continued proven success of our conference."

Part of the AAC's goal in targeting Mountain West teams was to destabilize the Group of Five landscape and solidify itself as more powerful than its peers. The AAC has long been considered the top Group of Five conference, but the loss of three top-tier programs in major media markets is changing that in a big way. 

With Boise State, San Diego State, Air Force and Colorado State staying put, the Mountain West has a core membership that will at least rival if not exceed whatever the AAC puts together following expansion, making it a contender for a regular spot in the proposed 12-team playoff. The proposed new postseason format calls for the top six conference champions to receive automatic bids, regardless of their status as a Power Five or Group of Five league.

With those four teams deciding to remain in the Mountain West, top expansion options for the AAC appear to be UAB, FAU and UTSA, Dodd reported on Sept. 16. North Texas and Tulsa were under consideration by the Mountain West should it lose two or four teams, though with the league staying together, it may not choose to add any teams.

Yahoo Sports' Pete Thamel first reported that the four Mountain West programs would stay with the conference.