Just to add to Tacoma's rundown -- Marco Gonzales' arm tightness required TJ and he's now on his way back, currently pitching at AAA Memphis. A cross between Vargas with 2-3 mph on the FB and Andrew Moore with the ++ pitchability. Word is his last couple of outings in Memphis have been MLB-quality.*
Although the Ms are already fixed for LHs with Paxton and Miranda, Gonzales is one of those heady, control-the-Zone players Dipoto likes. At one point before the TJ, he and Paxton were considered amongst the top prospect LHs, Paxton with more power, Gonzales with more craft. Because he's not yet 100% (but, as noted, still better than the Ms' alternatives), shifting Dyson for him with some balance pieces seems like a great stiffener for the rotation for 2017, with likely more to come.
Gonzales' dad is the Rockies MiLB pitching co-ordinator, so the kid has a lot of polish and a good head for the game.
* Some numbers from last 5 games at Memphis: 5W, 32IP, 34K, 7BB, 7R/ER, 22Hits, 2HR, 3HBP. Seems to be doing alright after not pitching in April and having a mediocre May.