I've never quite understood why Delta doesn't take better advantage of its SLC hub to serve a number of regional airports in the west which appear to me to be underserved:
Everett-Paine Field
Yakima
Salem
Klamath Falls
Eureka
Redding
Chico
Santa Rosa
Modesto
Monterey
San Luis Obispo
Bakersfield
Bullhead City-Laughlin
Prescott
Yuma
Santa Fe
Gallup
Amarillo
Lubbock
Midland-Odessa
Gillette WY
Sheridan WY
Lethbridge AB
Kamloops BC