Forbes Field (year unkown)

I can't seem to find a date for this delightful picture of Forbes Field from above.  Little info could be scraped from the faded stamp on the back of the photo.  All that could be discerned was that the photo came from the Carnegie, and was most likely purchased at some point in the early to mid eighties.

As far as the picture goes, I'm most fascinated by the densely packed parking lot at the bottom of the shot.  Assuming those are cars of the game's attendees, how long do you think it would free the central cars after the game?