Screaming or howling in Coconino County, Arizona

My daughter was visiting from out of state although she grew up here in Flagstaff. We decided one day to spend time with one of our hobbies which is photographing panoramic landscapes in Northern Arizona. We spent the morning in Sedona photographing the red rock country but as usual this time of year the monsoon thuderstorms came up around noon and we went back to the house to relax a bit. We did have significant storms in the area that day but late in the afternoon things began to clear up and we decided to head to one of our favorite spots for sunset photography. This was at the Arizona Snowbowl lower parking lot. The area from the parking lot to the west starts with a large lush green meadow before falling away into forest, meadows, and rolling hills (cinder cones)that stretch from Hart Prarie some 80 miles to the Grand Canyon. We set up our cameras anticipating a beautiful sunset and great opportunities to take pictures. there were a number of people in the parking lot area (10-15). A minute later two hikers started from the parking lot down through the meadow and I remember hoping that they wouldn't be standing in that meadow when I wanted to take a photo. As they traversed the meadow and passed out of sight we heard a single coyote sound off in their general vicinity. As the sun sank towards the horizon and we were getting ready to start taking pictures the two hikers came back from out of the woods and up through the meadow nearly to the parking lot. At that moment we heard a scream from the forest several hundred yards below us. There were people in the parking lot and two motorcycles idling right next to us. The scream was so loud that not only did we hear it well but one guy on a motorcylce looked at his companion (with motorcycles running and helmets on) and said "did you hear that-what the hell was that ?" We know that most people in that parking lot heard this scream. As the sun was now setting in a glorious fashion with thunderstorms around and off into the distance we got busy taking pictures. As the sun set and twilight began to overtake things most of the parking lot had emptied out except a pickup load of people had just showed up and they were half drunk and wandering around making noise. It was getting close to dark and once again we heard this scream from the same general area of the forest below us. The people from the truck said - " what the heck was that - a mountain lion ?" and began to laugh and talk nervously - I just wanted to say to them "please shut up" since if any other noises were made they would have been difficult to hear above their drunken mumbling and laughing. Finally they left - it was now dark, we hung around for a bit but not long and heard nothing more. This was not a mountain lion scream or anything else we could even begin to identify. It sounded somewhat like a scream a human could make but the distance it was travelling was significant. It started kind of low and built up. To us it sounded like the voices of 15 people all starting at the same split second and roaring the exact same note. It had a quality that one human could just not make, both by the volume and the effect of sounding like a group but clearly being one single scream or roar.