Ain't happening. At least not yet. Vermont tried, Colorado tried, both failed miserably. Single payer won't work unless you have the system to support it, which California most certainly doesn't have.
What they can do that will have a much higher chance of success is a public option and regulation on drug prices. From there, they can work towards a single payer system, or not if they don't want to.
To be honest, I don't know why everyone jumps straight to single payer when discussing universal healthcare in the US. It's certainly not the only option, and it is the most difficult to implement without giving any benefits other systems don't already have.
Still, good luck Cali!