Well, I finally found the location of the calling. Or, at least, the calling that matches the Hyla cinerea.

The bushes were far too thick for me to physically locate one of the frogs, but I saw the breeding grounds! It's a small ditch that filled in with rain. There are a lot of tadpoles in it, which really excited me, but then I noticed other frogs at the edge of the ditch. Proper frogs, or maybe even toads. Definitely not tree frogs.

The tadpoles are, to the naked eye, completely black. The body is quite circular and about 4mm each way, with the tail accounting for another 2mm. They are so black... surely these are the tadpoles of the frogs/toads I saw and not the treefrogs?

I tried to get a picture to identify the other frog/toad, but it hopped into the bushes too quickly. It was quite small. Perhaps the size of a large marble. Standard brown/black wild-type color.

I was so excited about gathering some tadpoles, and now I'm certain that these aren't the right ones!

Does anyone have a resource on what to look for in tree frog tadpoles versus other species?