Elementary, Watson! It appears the cab-end truck on Lehigh Valley C420 #411 has picked a switch point, thereby dragging the two adjacent locomotives off the rails as well.
And check out the guy on the right with the radio glaring my way! He seems to be trying to fog the film in my camera with that stare. They couldn't throw me out, because I wasn't on railroad property.
The track to the left is a remnant of a wye that once provided access to the LV branch to Perth Amboy. Better yet, there was another wye within the wye. There's a prototype for everything!