The University of Arizona appears to be on the throes of leaving the Pac-12 for the Big 12, per ESPN's Pete Thamel:
Pete Thamel @PeteThamelSources: Arizona is in deep discussions with the Big 12 about joining the league. Some finality is expected in the near future, as there's an Arizona Board of Regents meeting scheduled for later tonight.
Dennis Dodd of CBS Sports relayed the news as well:
Dennis Dodd @dennisdoddcbsSources: Arizona is now a "hard lean" to join the Big 12. Scheduled to be in executive session at the moment. No word on ASU.