Is this a software company building a campus? The only software companies that employ those types of number of employees are Microsoft, Oracle, and SAP. Even then most are sales and service and they are spread around the globe. Diversified companies like HP, IBM, etc who do software as a secondary business on are also spread globally. Just to compare, eBay, Google, and the like each have around 13K employees worldwide. 25K is a huge number.
If it's true, I'd imagine it'd have to be someone like Cisco wanting to move half their bay area campus to Socal, but there's no logical reason for this magnitude of a move with such little incentive.