Well, this is migration period and that bird is probably in OK by now on its way to Texas for the winter.
There is a higher probability that it is a buteo, and that could mean more likely a red-tailed or ferruginous hawk, but the grey on top is the complication. In the back of my mind, I've been trying to remember something about cross-breeding among species, which can complicated identity. Some buteos do cross breed, and I found site that does mention that -
Ferrugenous x Redtail Hawks - http://www.shortwingfalconry.co.uk/hawks/ferrutail.asp
Here is some more information and pictures -
http://sdakotabirds.com/species/ferruginous_hawk_info.htm
http://sdakotabirds.com/species/red_tailed_hawk_info.htm
For more species -
http://sdakotabirds.com/species_main.htm
Some nice pics - http://www.schmoker.org/BirdPics/FEHA.html
http://www.schmoker.org/BirdPics/RTHA.html
Schomaker photographs birds using a Nikon D2X with 200-400 f/4 AF-S VR and 80-200 f/2.8 AF-S VR lenses with TC-14E and TC-17E teleconverters