It's strange that the native populations of the Americas left virtually no lasting monuments outside of the serpent hills of the southern Atlantic N.American coast, the Anasazi dwellings of the Southeast US, and the Mayan and Aztec constructions of Central and South America.
But...
Though strictly utilitarian (mainly a way of having a place to put stones dug up in the preparation of farmland) the running stone walls in my locale have become a sort of mystery of sorts, as so many of them are now found deep in the woods, the farms within which they were originally circumscribed having been abandoned two hundred years ago.

My late friend Peter and I even once found a buried stone cellar that in our childhood we'd walked over many times without being aware of.

Not as cool or ancient as wot this thread deals with, I know. Someday I want to return to the UK and do some visiting to the megolythics. But it's always cool to be walking out in the deep woods and suddenly find these running evidences of old habitation.