I never saw the upper side of its wings. At first, I thought it resembled some pictures of crescents I saw, so I was lucky to stumble upon the pictures of the blues. (I care enough to sort of want good ID guides, but not enough for it to make sense to buy them, so I have the semi-laborious look-on-web method, but, hey, it's still our one little bit of crazy utopia compared to pre-web when you thought "i wonder what kind of butterfly that is" and you just had to be content merely to wonder, which sucked.)
The timing makes me think Spring Azure sounds likely.
another one (1/3) A bit more looking up of info and the Northern Blue looks most similar among what I saw.