Voices in Coconino County, Arizona

I am actually kind of hesitant to post this report since I couldn't verify what animal was making the noise we heard. I didn't check for footprints or observe any movement on the slope that might have indicated what animal was producing the noise. We were driving back to Utah from Phoenix after attending the funeral of an old family friend. The only people in the car were my 10 year old son and I. My son has a fascination with science and more particularly earth sciences so I decided to show him the volcanic craters around Sunset Crater north of Flagstaff, Arizona and also to see the ancient ruins of Wapatki National Monument which is on the same road that breaks off of highway 89 and then rejoins it several miles north. We drove past the turnoff for the campground west of Sunset Crater and then stopped on the road that cuts into the northern slope of Sunset Crater right where a ridge of lava juts out of the ground (on the northern side of the road from the slope of the volcano) like a frozen lava fountain. This lava ridge is the beginning of the Bonito Lava field that extends north-northwest of Sunset Crater. I parked the Montero against the slope since there wasn't enough room for a road shoulder and several cars passed during the incident. My son wanted to climb the lava ridge and I stayed at the base using the camcorder to film him. While walking to the ridge I kept hearing a very heavy, breathy huffing noise coming from the slope of Sunset Crater slightly southwest of our position and above us on the slope. It would repeat every five to ten seconds and I caught my son, on video, standing on the top of the lava ridge, looking back at the slope where the noise was originating, pointing at the location and saying "I think I heard something up there" and I responded "I did too, I don't know what it is" and my son replied "I think we must get out of here" and I responded by kind of nervously chuckling it off and continuing to film. I was a bit uneasy since it sounded like a very large animal and I was unarmed in defense of my only son. Unfortunately in reviewing the video, I can't hear the huffing but it sounded like an animal that was passing a large volume of air in an angry huffing (I have had several bear encounters and none of them ever sounded like this) that didn't want us there but didn't seem to want to draw too much attention to itself (my speculation) since there were several people in the campsite/turnout around the bend of the road west of our position that probably couldn't hear this noise. It sounded quite capable of making much more noise than it was doing. Walking back to the car I tried to imitate this noise out load without success but the noise from the slope ceased with my attempt. The pine trees in the area and on the slope obscured my view of the animal though it obviously knew we were there because we made no attempt to mute our voices and my son's excitement for being there showed in his voice. The exact location where we parked is 35 deg 21' 59" North 111 deg 30' 34" West.