What Is This?

Unknown thing- 
This immovable metal object sits at one edge of our clearing, atop a small plateau.
As I've mentioned before, we live in what is commonly called "Gold Country," in the California Sierra foothills.
I researched the history of our property and found this particular parcel wasn't bought from the Bureau of Land Management until March 3, 1919, by one Charles L. Wetmore.
Most of the surrounding parcels had been bought much earlier, and had been used for farming, quartz mining and gold mining.
In fact, the 1920 census for this area had an interesting notation along the border where the census enumerator normally would write the street name, and address. It said "Farmers And Miners All Over The Woods, Vicinity of ________ _____ Road."
Charles Wetmore's land was later subdivided into five acre parcels, and our home wasn't built until 1982.
Could this object be debris from some (probably illegal) placer mining?
Maybe it's just abandoned equipment from the grading and building of the house?
A friend suggested I plant some flowers inside, and that's a wonderful idea... except for those doggone deer!