The difference between the (northwestern) crows and ravens in North America is difficult from a distance if you don't have a way to judge the relative size, but when viewed through glasses or close enough to see the sheen on the feathers, I've always thought ravens were a bluer-black than crows, and they're a heckuva lot bigger. The tail is different. Crows in the northwest are apparently smaller than some others, so perhaps I saw a larger contrast--I haven't seen any ravens around here in order to make such comparisons. Grackles are a more diminuative member of that family (though I don't find them on this list I've linked to).

SRS