The County has the sole authority to rezone land.
There is a reason Toyota didn't sell the land to home developers.
The land is considered toxic for residential use after 40 years of ICEv manufacturing.
It would take a reclamation project and about 20 years before it meets residential standards.
At the time Toyota sold the factory to Tesla the reclamation project was estimated to cost $750M to $1.1B.
And the land was said to be worth $1B if it was rezoned residential.
Toyota didn't want to be affiliated with toxic reclamation project for 20 years, nobody else wanted the property, so they sold it to Tesla for $42M after agreeing to invest $50M in Tesla.
Apart from NUMMI how many unused car factories were sitting around for sale in California when Tesla was looking for a production facility? I mean, to get one for so little right in an area with so many software developers that Tesla also would need, seems like a really good deal.