Here's a comparison female Black-chinned from Arizona showing its blended face and longer bill.
A character that I guess I should study more is the color of the forehead and cap. Pyle says that Black-chinned lacks green tones; its cap is brownish or gray. Honestly I don't see a lot of green here so clearly I should look at more young hummingbirds next fall.
One of my pics early on seemed to suggest a purplish gorget feather which would be very strong support for Black-chinned.
I don't honestly own a specialty hummingbird guide. Allen Chartier said that a young Black-chinned should have buff edged primary coverts which this bird clearly does not (apologies if I over-simplified, if so blame me, not him)
A view of the only shot I lucked into of the spreadtail.
If a person knows what they're doing the shape of the outermost primary likely cinches this as a Ruby-throat. Unfortunately I have far more frozen wings of Costa Rican Hummingbirds than I do of the one in my backyard...