Tesla recently finalized its purchase of the advanced (and apparently extremely clean) NUMMI production facility in order to build its upcoming Model S sedan. Tesla hopes to build as many as 20,000 units per year in the southern California facility that's capable of building one million units annually.
Other than some potential spin-offs using the Model S platform (like an electric GT), there's a lot of capacity. That's where Toyota steps in. Toyota and Tesla will be working together to develop electric vehicles. their parts, and the engineering behind them.
The new facility will hire up to 1,000 new employees initially from one of the brightest pools around: Silicon Valley.