plants: Mystery Mint

UPDATE: I'm pretty sure this is American germander, Teucrium canadenses. The Wildflower Center entry says that it likes moist soil, which would explain why I always see it around creeks and why it's doing so well this spring/summer.

Anyone know what this plant is?

It's definitely in the mint family, as it has square stems and spreads with underground runners. Plus, the flowers are very minty fresh. (That makes it sound like I've tasted them, which I haven't. But it's not a true culinary mint, whatever it is.)

This is a pass along plant given to me by an old neighbor who said it is native. I've also seen it growing down by the creek. (Neither of those data points mean that it is actually native.) She told me the name, but it's now escaped me. The plant, which started as a few twigs planted in the far front corner of the front garden has been really benign for about 4 years. But all of a sudden, it's going gangbusters (and spreading like mad)!

It has a nice form in mass, and I imagine that when all of those blooms open, it'll be a beaut and probably attract lots of bees...