Mark- be careful in those woods. ticks are notorious now which cause lyme disease, I just noticed your videos. Hope you are ok. I was born in Aliquippa,
They used to store road salt in this area. But closer to the smoke stack, I believe. Edit: I just looked at the location on Google Maps, and I will make a guess that they cut out that cut there as a way to unload the salt from railroad cars! The'd probably back dump trucks up under the tracks, unload the hoppers, and then drive them up to the pile, which was where that big open space was. I also wonder if those giant concrete shapes were used as stackable retaining walls to hold the salt together.
I really wanted to watch your video, really I did. However the camera wide-angle fish eye is rough and the audio has a lot of clicks that makes your video unwatchable. Please go back and redo the shoot with improved video and audio settings, then I'll be sure to tune in.