Screaming or howling in Placer County, California

Well, I've had a story to tell for quite sometime. I belong to a world war two battle reenacting club for seven years now. The place where this happened we have been going to before I joined the club. The people in the nearest town of Foresthill know this club well. The story I'm about to tell you is true and the people involved are veterans of the hills of California. It was back in 1998, the second weekend of September (I know this because we always meet on the second weekend of the month). Anyway, on Friday night, I was on my way up to the site to set up camp for next day. When I got up there, my unit commander was already there, so after we got done, we bedded down for the night. Before you knew it, it was morning and all through the night we kept hearing cars and trucks pulling up. The next morning we woke up to everyone there (all four units worth). All that day, we battled from dawn until dusk. When we were done, all tired and bruised, we managed to drag ourselves back to camp for dinner. Some went into town, the rest of us stayed and had it there. Later, we were all back and sitting around four different fires and talking about the day. One by one we went back to our tents or cots and sleeping bags. The last thing I remember before I went to sleep was both of the commanders talking about tomorrow's set up and that was it, or so I thought. Well, I was rolling over in my cot and slightly awake when, well for the lack of a better word, heard a "howling sound". I, in all my life, have never heared anything like it before. It cried out eight or nine times . After a few moments there was nothing, so I got tired and went back to sleep, but only because the sound wasn't too close to the camp. It sounded like it came from where we where battling that day up on the ridge, about half a mile from us. I woke up again about one hour later. I had to use the bathroom, I put on my boots and walked over to a bush to relieve myself, and on the way back I heard it again, but this time it was much closer. It was right down the road from us and it was loud, very loud, and I know that this time I wasn't the only one to hear it. Several times it let out . one after another. This time it was much more deep and clear to the ear. My unit commander and several of the other unit people woke up. To my and their knowledge, we didn't know what to do . No matter what I did, I could not stay awake but before I went back to sleep, I loaded my gun with real bullets and put my bayonet under my blanket near my pillow. What ever it was, if it came into camp and hurt me or anyone, I was going to kill it. We heard it two more times that night, each time it was further away. When we woke up that next morning, many people were confused and in denial about what happened. We all were trying to think of what it could have been, but no one said what was on everyone's mind. To this day it gives me chills up and down my spine at the thought of what we all knew it was.