Cal has already lost cornerback Cedric Dozier by transferring to Kansas State. Now graduate transfer Michael Barton will be taking a look at the Arizona Wildcats.
SF-Tuscon— Michael Barton (@michaelbarton08) January 29, 2016
This wouldn't be the worst thing in the world for Cal. Barring a Pac-12 championship appearance, the Bears do not play Arizona in 2017, so Cal would not have to worry about losing to a Bear.
As you might remember, Cal blocked Dozier's attempt to transfer within the Pac-12; Dozier apparently hadn't fulfilled all his graduation requirements at the time of the transfer, so he wasn't able to move as a grad student. Barton has already fulfilled all his requirements so he is not subject to any such barriers.
In terms of intraconference transfers for Cal in the Dykes era, this would be another major one for the Bears, the most infamous being Brennan Scarlett's grad transfer to Stanford. After the 2013 season, Johnny Ragin also made the move to Oregon, as has Freddie Tagaloa to Arizona.
UPDATE: Barton transfers to Arizona.