I've got my eye on you

I believe this is a falcon. In my bird book it looks just like the gyrfalcon, but the description says they are 20-25 inches (51-64 cm) and this bird did not seem that big. He was on a pole though and up pretty high so maybe I couldn't judge his size very well. I don't know. Anyone hazard a guess or know for sure? This isn't the best pic, it was getting late, but I like it because he didn't fly off when I stopped and pointed the "big gun" at him.
Taken at Baskett Slough.