I just saw that California may actually be voting on secession.

Many may say "good riddance". I could see a few problems:

I would assume it would be impossible to build walls to border in the state.

Without a significant new revenue stream to replace whatever federal funds California gets now in all its forms, it would most likely turn into Venezuela Jr. Where would it get that revenue stream? After the implementation of a $15/hr minimum wage, apparently that was the nail in the coffin of many Bay Area restaurants which are going out of business at a rapid pace with residents scratching their head as to why.

Perhaps it would partner with Cuba, China, Iran, "Palestine", etc to allow for missiles to be placed on its soil pointing at the rest of the U.S. Let China build a military base, naval base, etc on California soil? Lucrative rent/revenue I would imagine.

Maybe California would agree to be annexed by Mexico furthering the drug cartel controlled land areas

Or....maybe the measure would go nowhere.