Gallen will start Arizona's spring opener against the Rockies on Sunday, Steve Gilbert of MLB.com reports.
This is the first hint at how manager Torey Lovullo plans to sequence the rotation, although there has been no official word about the rotation order for the regular season. Gallen and Madison Bumgarner were speculated to be in the hunt for the No. 1 job, while Caleb Smith could also slot in at the top end of the order.