In February of 2014, it was reported in L.A./Orange County media that the Angels had begun negotiations with the City of Tustin to build a ballpark on the site of the decommissioned MCAS Tustin (nee MCAF Santa Ana).
This was the base plan prior to the Angels expressing interest in building a new ballpark at the site:
The Orange County Register reported that the initial parcel in question was at the western corner of the base.
The Register reported earlier this month that negotiations are still ongoing via an awkwardly-worded update in an article largely focused on the city's pot ban:
Hopefully city planners have come to their senses and realized that the best location for a stadium at the base would be at the eastern corner, closer to the Tustin Metrolink Station (obviously, such a change would require renegotiation with the other developers already engaged with the city).
I'm not sure if this is going to happen or not, but 2016 will be an interesting year for the Angels' future in Orange County.