The flying that OO
took over was already existing capacity- It was previously flown by QX
Alaska Air Group wanted the cost benefit of operating Horizon Air with an all Q400 fleet. Certain markets that Horizon had flown with the CR7 however weren't fit for Q400 service (just too long) and therefore AAG looked outside the family for another regional.
Not sure how much longer Horizon Air will even be around- Skywest is certainly looking for the business from Alaska and if they can prove they can do this flying successfully, maybe they will look for more Alaska markets they can serve.
As far as SLC
goes I don't see why AS
needs to have a physical presence there when they have the codes via their DL
codeshare agreements- OO
CR7s can be rotated through CA
maintenance bases I'm sure- such as FAT
- and don't have a lot of reason to visit SLC