Or "northern Cal". Both were common as I recall. I use "Cali" online these days cuz it's helpful in distinguishing the State from school names. And probably cuz I've been simply influenced by common online usage.

But I never say "Cali". It was never anything I heard in my years in California. Maybe a time or two — but nothing that was standard lingo. I've heard it plenty in Utah over the years, though. I wonder with how many others that's the case.