Buteo swainsoni. This one followed me for quite a way this morning along the road. I was cutting off into the roadside brush every now and then and I think he thought I could be a good critter-flusher for him. (That's why you see so many raptors staying close to the medians on the Interstates.) I would stop to photograph something and he would light on a fence post and wait for me to move on. Pretty self-assured dude.
I've seen Swainson's beat up on Redtails, a much bigger bird. They are swift flyers, very agile, and quite pretty with beautiful coloration. We have a lot of them.