Toyota Motor Corp. reportedly will close its New United Motor Mfg. Inc. plant by March, marking an historic move for Toyota and ending months of speculation about the fate of the last vehicle assembly plant in California.

The Los Angeles Times reports Toyota’s board of directors notified Fremont government officials today the plant would be closing in March 2010.

The Fremont-based NUMMI builds the Toyota Corolla compact sedan and Toyota Tacoma compact pickup truck.

NUMMI had been a 50/50 JV of Toyota and the former General Motors Corp. The new post-bankruptcy General Motors Co. announced in June it would no longer continue as a partner at the plant, which it previously wholly owned before the creation of NUMMI in 1984.

GM last built the Pontiac Vibe compact hatchback, a twin of Toyota’s Matrix model, at NUMMI. GM has announced it is discontinuing the Pontiac brand.

NUMMI employs more than 5,000 direct workers and becomes the first Toyota manufacturing site to be shuttered in North America.

The plant’s unionized workforce, with reportedly higher-than-average Toyota manufacturing wages, has been thought to be an Achilles’ heel to keeping it open, as is the high cost of manufacturing in California.