SAN is too far down south for a hub, and the airport is too small
. Perhaps as a point where aircraft can be based when a new one is built here though.
Right now if an airline wants to have a chance in the West, it would have to cater to high-fare business travelers, as there is too much capacity in the economy sector of the marketplace. If you look at schedules that include flight availability statistics, you will find that often the first sections of flights are always full within CA and up to SEA and PDX while the coach sections usually have tons of seats left. So that means if CO would want to have a chance to succeed greatly out here, it would have to do an overhaul of its cabin and other passenger services. I would think that if it had the aircraft, TWA could do well on the West Coast b/c of the amount of first-class seats in its planes.
Airports, as already mentioned, are a huge problem. SAN is too small and too far down unless you wanted to include Baja and N. Mexico in your scheme, LAX too crowded, SNA to restricted, ONT to far out in the boondocks, and SFO, SEA, PHX dominated by UA, AS and AW, respectively. So that leaves pretty much SMF and PDX. I think that a problem with DL at PDX was that they didn't expand it enough domestically, with a viable shuttle system up and down the West Coast. This may have been because it was too close to SLC. I bet that if CO had the aircraft, it could create a good operation out of PDX, but as has already been said, Continental is concentrating on IAH, Europe, and COExpress now.
SMF is an interesting choice, with a very good location, but I think that if a hub was built there it would only be for the purpose of filling planes with connecting passengers, rather than a stable combination of connecting and O&D pax.