Someone left the hose running in the pond, which created a muddy patch to its left, and look who showed up to gather some mud for nest-building. The first image was by avatar99, the second by rafa:
It was ID’d as a Barn Swallow, which I think I can go along with. I wish the tail was more visible in the shots. There doesn’t seem to be a pale collar, which would tend to rule out Cave and Cliff, but what you can see of the underparts seem pretty light-colored for Barn. Then again, Sibley talks about the female Barn Swallow having both lighter underparts and a shorter tail than the male, so that sounds pretty good.
Anyway, if they’re building a nest they’ll probably be back. All three (Barn, Cave, and Cliff) are possibilities based on the Sibley range maps, so let’s keep our eyes on the mud puddle!