There's something melancholy or ghostly about those abandoned homesteads and such. They represented someone's hopes and dreams. There sure is a lot of abandoned industrial equipment out there too, representing a lot of capital investment, too. Getting those boilers and rock crushing machines, simply getting all that stuff transported to the remote deserts and high country was no mean feat in those days. Here in the midwest, wooden structures soon decompose, and iron and steel isn't far behind. The dry desert or mountain air keeps things in kind of a state of suspended decay or preservation.
I found some cool unexploded ordnance in the backcountry of Hawaiʻi Volcanoes NP.
During WWII, they did some bombing tests in the area, and there is still a lot of the old stuff out there.
There is also a lot of old ammunition all over the place. I basically found these cases every few hundred yards on the lava in a remote area of the park.