Tesla battery factory courted by Tucson, Ariz.

Tesla recently announced plans for a lithium battery "gigafactory" and is considering four southwestern US states for its location. The city of Tucson has made a formal proposal to become the site of the Tesla giga plant.  

Tesla Motors recently announced plans for a battery "Gigafactory," which is to provide enough lithium-ion cells to allow it to build a projected 500,000 electric cars per year by 2020.

That would require far more cells in its preferred format than last year's entire global production, hence the need for a massive U.S. factory.

The question is: Where will it be located?

While Tesla named several four states--Arizona, Nevada, New Mexico, and Texas--one of them is now actively and publicly petitioning the automaker.

The Arizona Daily Star reports that Tucson is going after Tesla. The city has made a formal proposal to become the site of the giga plant, which is expected to employ 6,500 people.

Tucson Mayor Jonathan Rothschild told theStar that a site near local highways and the Union Pacific Railroad mainline has already been chosen, and that the city has prepared tax incentives on top of what the Arizona state government would offer to entice Tesla.

Tesla previously said the giant factory will cover 500 to 1,000 acres and will include every stage of battery cell and pack production. The price tag for the entire project is estimated at around $6 billion.

Notably absent from the planning process is California, home to Tesla's headquarters in Palo Alto and the assembly plant in Fremont that builds the Model S electric luxury sedan.

However, Tesla has said the Golden State is not in the running for the Gigafactory.

That may be because--while Tesla may have started there--Silicon Valley isn't ideal for green carmakers.

Strict environmental regulations make manufacturing anything difficult in California, and could make the world's largest lithium-ion cell plant a non-starter in the state.

The new battery packs built in the gigafactory are expected to go into Tesla's next-generation sedan and other future models.

Known for now as the Model E, the sedan will be significantly less expensive than current Teslas, partially due to the 30 percent reduction in cell cost per kilowatt-hour afforded by the massive plant.

A recent Navigant Research blog post also considers the idea that--rather than ship completed battery packs to the current factory--Tesla will bring the factory to the packs.

Once a site is selected, Tesla hopes to begin construction by the end of this year, with production launch and ramp-up starting during 2017.