Prairie Falcon for sure. Peregrine's have a larger and darker 'mustache' as well as overall darker body marks. It also appears to be eating some sort of small mammal which is the Prairie Falcon speciality compared to the Peregrine that specializes in avian prey.
Thank you all very much! I have been trying to figure this out for a while! I was not even considering the correct bird.
I live in Downtown Denver ( 5 points ) and it never ceases to amaze me the wildlife encounters I have in the Flatirons, many trailheads being less than a half hour from my front door. This was an after work scamper.
This bird did not like us being up there and even more it did not like the other birds flying around. It let out many screetches at all of us. It was also very large.
I'm guessing the thing in its tallons is either a squirrel or a prairie dog, too small to be a chipmunk.