What is this?

I did a traverse of the northern Du Cane Range with a friend in February this year. While scrub bashing up onto Falling Mountain above Du cane Gap, we found the pictured item laying in thick scrub below the tree line. It is steel, possibly stainless, given that there appeared to be no rust. The question is, what on earth is a heavy chunk of steel plate doing sitting in the bush just there - most weird!
If you want to see a few more pics from the same trip, they are at:
http://mchugh.gallery.netspace.net.au/DuCaneCircuit
If you want to see a few more pics from the same trip, they are at:
http://mchugh.gallery.netspace.net.au/DuCaneCircuit