All the concrete will do is just make a blob like a scab, and only on the surface. Good thing you don't have earthquakes back there or that building, and everything in it might be part of the hillside.The building's main means of support is a couple feet in on 10 year old fill (slate and some dirt), the support you see is just me helping it out since there is some weight in that corner. I'm sure it will settle some more so I'll be out there again. I may dump a couple bags of concrete on/in the rocks and water it.
And I'm glad you didn't fall down that thing. That would be an experience to remember for eternity.