California has a budget surplus compared to a federal government massive deficit. California sends more money to the feds than they are given. It is one of the most dynamic states and has all of the american tech companies that are today the largest economic advantage the US still has in the world. Also there's a large part of the american but also international scientific brains that live in the state.
An independent California would probably converge to something like a Nordic country rather than a liberal downhill country as Deutsh thinks. Only difference is that it would be the world's 6th economy with still a lot of growth potential.
The truth in America is that a most states are seriously degraded when it comes to economical dependency on federal money, public finances and general living conditions. California, Texas and New York are responsible for a third of the nation's economy. Take any of these out and it's very likely that you'd be in serious trouble.