Found this feather at the foot of one of the tall buildings here.
Had an instinctive hunch that it was a falcon feather.
Went to the U.S. Fish & Wildlife Service Feather Atlas.
You can narrow your search by Unpatterned, Two-Tone, Mottled, Barred, Spotted, Colorful Iridescence, Dark Tip, or Pale Tip.
And the colour.
Chose Barred and Gray.
And the best match I found was....Peregrine Falcon.
So my hunch was (I believe) right. Maybe I know more about feathers than I think. But, given the size of it, and given the makeup of bird populations in the downtown area, it was a pretty reasonable guess.