Report 1251: Threatening bellows directed at hikers and their dogs in the Holy Cross Wilderness

My girlfriend and I were hiking the Lake Charles Trail in the Holy Cross Wilderness area.  We had hiked approximately 3 hrs/6 miles when we reached a basin which included 2-3 small lakes.  Upon reaching the basin area (a clearing) after climbing a steep switchback, we immediately heard what sounded like a loud scream coming from approximately 50-75 yards away in a dense pine cluster at the base of a mountain.  The sound grew louder as the animal was moving in a diagonal to us through the pine cluster somewhat towards us.  The vocalization now sounded like a large man wailing or moaning in a loud, rhythmic pattern.  The vocalization would last for 2-3 seconds then pause for 4-5 seconds then start up again.  This went on for 2-3 minutes.  I am an avid hiker and outdoorsman and am familiar with animal vocalizations including bear, elk, coyote, and mountain lion.  I can say that what we heard was not an ordinary animal.  I had with me two dobermans that have a tendency to chase a moving animal however, on this occasion, they were motionless showing a curious stance and looking in the direction of the sound.  As the sound grew louder, I became extremely frightened due to the volume and unknown nature.  I leashed the dogs and reached for my pepper spray as the sound moved towards us.  I cannot emphasize enough the rhythmic nature of this call and sheer volume.    The vocalization eventually stopped and we continued our hike.  5 minutes later, we passed a White River Forest Ranger, "Lisa", who we questioned regarding the vocalization.  She had heard it also and stated that in her years of service, she has never heard a sound like that before.  She had no idea what it was.