CA has the advantage of geography - any invading army would have to cross the steep side of the Sierras. These have relatively few passes, most at high altitude and all easily defended against an invading army. It's actually easier to invade CA via Tijuana than overland through the U.S.
They also have the advantage of being exceptionally technically advanced - perhaps moreso than the U.S. military, given that Lockheed has a large presence in the Bay Area and all the Predator drones are made in San Diego. And they're a nuclear power - Livermore is one of two sites that actually develops atomic bombs.
This'd be fun to wargame out as a board game or computer simulation, although the subject matter is a little macabre.
If this little wargame is to be played it would likely be a battle of attrition US warships deploy to restrain trade and cut off the CA economy... assuming the leadership isn't removed somehow by assassination or coup attempts.
CA is a big part of the US economy and culture, but in no way would I imagine that it could resist the rest of the 49 states.
You have to consider that it's highly unlikely that everyone in CA would be in favor of secession. I can imagine that many people in the Central Valley, who tend to be far more conservative than their coastal counterparts and rely extensively on Federal farm subsidies as well as out of state water resources would be less than thrilled at the idea. These people also tend to have high rates of firearms ownership so I could see a nice little insurgency springing up.
Certainly there is a lot of high tech industry in CA but I doubt that Lockheed and the other defense corps are disproportionately reliant on CA, they have plants and R&D centers spread throughout the country.
They also have the advantage of being exceptionally technically advanced - perhaps moreso than the U.S. military, given that Lockheed has a large presence in the Bay Area and all the Predator drones are made in San Diego. And they're a nuclear power - Livermore is one of two sites that actually develops atomic bombs.
This'd be fun to wargame out as a board game or computer simulation, although the subject matter is a little macabre.