http://www.flatrock.org.nz/topics/flying/douglas_dream_in_santa_monica.htm
I worked next to the plant until it was pulled down (and parts blown up) in the 70’s. The older residents back then remembered the fake roads over the roof.
I did not learn about it until I was poring through archives of the company newsletters of that time. I was trying to find info of my Dad, who worked there then and later. I did not find him, but lots of other fascinating info. The Douglas plant was a community unto itself. My mother said, the job she loved best ever.