From a Tesla press release:
In June, we broke ground just outside Reno, Nevada on a site that could potentially be the location for the gigafactory.
Consistent with our strategy to identify and break ground on multiple sites, we continue to evaluate other locations in Arizona, California, New Mexico and Texas. The final site for the first gigafactory will be determined in the next few months, once we have full visibility and agreement on the relevant incentives and processes for enabling the gigafactory to be fully operational to meet the timing for Model 3. We see these concurrent efforts as prudent. This vehicle will be our third-generation product and will substantially broaden the addressable market for Tesla, helping to accelerate the transition towards sustainable transportation. Any potentially duplicative investments are minor compared to the revenue that could be lost if the launch of Model 3 were affected by any delays at our primary gigafactory site.