<PERSON>
The person who wrote up the synopsis you see on letterboxd must have slept through the movie. Even the little girl at the end knows that "the harpies were not Indians".
The film teases you with both possibilities: that the inexplicable goings-on are ghosts held by the forest, or people held by their own madness and evil.
It's fun to ponder the latter. <PERSON>, who the film's lesser narrators--the children--see as a magic fairy, basically offers a human explanation of fairies. Some folks reject religion, or "progress", so thoroughly that they just go live in the woods. <PERSON>'s path to that point involves acting first as a crime scene detective. <PERSON> eats dirt--something we would pathologize as "pica"--but her work is not substantively different from that of modern footprint or chemical analyses. 295
Her methods also involve attempting to recreate the costumes of the valley's attackers: she dresses herself in feathers to balance the attackers' wood-and-mud camouflage. (The mud itself is revealed to have makeshift poultice qualities, generally healing the bodies of those who hide and sleep in it--unless, that is, their wounds are large enough for insects to infest the body.) <PERSON>'s work reveals to her that the previous group of settlers* had experienced infighting that led to fatal violence. Her final discovery is that those settlers had been holding toads in their mouths for their psychedelic qualities. If this wasn't the genesis of their madness, it certainly kept them that way.
The Shawnee concept of demonic activity--evil pools underground in certain places--makes the valley, in this "natural" explanation, a place where the chemical runoff of the forest collects, and makes both "healing" pools as well as animals who have become semi-poisonous in the course of their evolution.
But the preacher sees everything that is easy to get as a gift from God. A ruined shelter in an empty valley is divine provenance, not--as Marion can see--a clear sign that the place is unlivable and avoided by the locals. As <PERSON> tells us at the end, the smart thing to do is recognize that the valley has some good qualities, from afar; because, without an understanding of the environment, you will always be burned by it.
*were they French? 45