[dragonwriter]

> If this were to actually pass in the State of California, would the only thing necessary after that be for the US Congress to accept six new states into the Union?

Probably not; even if the ballot measure passed it would still probably have to pass the state legislature: the US Constitution requires consent of the State Legislature (not just "the State") to form new states from the territory of existing states, and in other circumstances (the similar restriction regarding rules for choosing Presidential electors), ISTR that the federal courts have looked specifically to the Legislature.