I was on my first hike-in trip, and we got totally fucking lost because, unknown to us, they had been logging in the middle of what was once a well-marked but privately-owned trail. So we came around one turn and it was just bare hillside for a mile or two, covered in mud due to root loss and recent heavy rain. Anyway, we got totally lost. Our scout troop leader, who was an Army Ranger and tracker, found us a decent spot for the night, but we were all sort of on edge. We were perched on this deforested edge so steep that my brother's tent actually slid a good 10 feet overnight, and we had to set up in the dark, and it was cold and raining. Overall pretty terrible.
At about 2AM, the entire camp of about 15 boys and 4 adults got woken up by the sound of this long, drawn-out horrible screaming from the other side of the valley. We had no fucking idea what it was, but EVERYONE heard it. The guide (Navajo-trained tracker and former Army ranger) had no idea what it was. He said it was probably a bird, but years later my dad said that the guide had reported it as a woman screaming when we got back home.