Elon Musk is working on something out-of-this-world in Los Angeles.

The founder of SpaceX has spoken for years about building the Big Falcon Rocket: a giant reusable launch system designed to get people to and from Mars (and perhaps around Earth).

Most recently, Musk said SpaceX hopes to begin short up-and-down launches of the BFR system's 157-foot-tall spaceship in early 2019. The testing will occur on the company's McGregor, Texas, campus.

Until now, however, SpaceX has been mum about where, exactly, it plans to build such enormous rockets.

On Monday, a member of the r/SpaceX community on Reddit noticed a curious move by the Board of Harbor Commissioners in Los Angeles. The organization recently and quietly approved a 788-page plan by SpaceX to lease an 18-acre site in the Port of Los Angeles, including a 200,000-square-foot facility to "to manufacture large commercial transportation vessels".

Eric Berger at Ars Technica has since anonymously confirmed that the facility "is, indeed, intended for the manufacture of the BFR."

A source close to the matter told Business Insider that SpaceX is likely just weeks away from being officially offered a lease to the site.

Here's what we know about the proposed plan, and what SpaceX's "state-of-the-art" Mars rocket factory may look like when finished.