This raptor was flying back and forth high above screeching loudly for at least 20 minutes indicating it probably had a nest high up in the cliffs. It finally stopped and took this perch after we had passed the cliffs. Michael who knows his birds identified it as possibly being a Kestrel after getting back to camp and digging out his Birds of AZ book. We didn't have a clear look at the bird as it kept considerable distance from us. This zoomed photoshopped photo shows details of the bird that we couldn't see at the time. I'm thinking it might be a Peregrine Falcon but am waiting for confirmation from Michael.