A 19-acre site at the Port of Los Angeles populated by dilapidated buildings and rusted cranes is playing a key role in SpaceX’s long-standing plan to colonize Mars. In two to three years, hundreds of workers could be swarming over SpaceX’s massive BFR rocket and spaceship system there.About 20 miles north, at SpaceX’s Hawthorne headquarters, thousands of employees already build Falcon 9 rockets and Dragon spacecraft...