Tesla bought an old GM-Toyota factory and made it cool - but in its former life it built a lot more cars

Looks can be deceiving. NUMMI was perhaps the most important plant in automotive history, after Ford's legendary River Rouge factory.

It actually dated to the early 1960s, when GM opened it as Fremont Assembly. By the mid-1980s, it had been revamped through a joint venture between GM and Toyota. In fact, NUMMI was essentially a separate manufacturing company.

The goal for GM, in particular, was ambitious: learn the by-then famous Toyota production method, which combined continuous improvement of manufacturing (the Japanese concept of "kaizen") with so-called "lean" or "just in time" production.

The idea was that much greater efficiency, cost savings, and quality control could be achieved if parts inventories were kept light; materials would arrive "just in time" at the assembly lines.

Sounds good, but it required a very high level of supply chain management and workforce training. It's the opposite of "vertical integration," the system of doing everything in one place that defined the auto industry before Toyota disrupted the paradigm.

Ironically, Tesla CEO Elon Musk now wants to take Tesla's production back to the vertical model.

NUMMI was closed down in 2010.