Here: https://en.wikipedia.org/wiki/Yes_California#Polling

Roughly 60% to 70% say "No". So, it's unlikely to happen any time soon.

Watch out for that assumption.

I believe at the end of 2015, a few months before the Brexit referendum, about 70% of people were indicating they'd vote remain in polls. That's the only reason Cameron and the rest of the Remain-supporting political class allowed a referendum at all: they were sure they were going to win.

Turns out that intense discussion, debate and political campaigning can change voter's minds. That's the point of it in fact. Who knew?

Same place Scotland separation is, except perhaps that now Scots probably think they were wrong to vote to stay.

California is more likely to split into multiple states than it is to succeed.