Google historical railfanning ...
Go to the Long Beach Airport, Boeing plant side. Here: [
www.google.com]
Browse around.
There was certainly rail service from the north. In fact, the rails still almost get there - they end at a lumber yard just north of the Boeing site, across Cover St. From the end of the rails, obviously paved-over track space extends southward into the Boeing site, curving through what's now the west side parking lot. There also apparently was a wye at Cover St., with a line extending east to more industrial sites (now mostly vacant) in the NE quadrant of the airport; some obviously filled-and-paved tracks are visible in that area. When it all was torn out, I don't know, but some historical Google picture perusal might give a clue.
Side note: the current Google picture should probably be saved for historical purposes. It includes a C17 rolled out, which might be the last one or nearly so. Oh, and another one is at another Boeing site on the south side of the airport, apparently being worked on: [
www.google.com] . And check out to the west (left) - somebody apparently is fixing up DC-3's.