Top one may be Schizachyrium scoparium, or similar. Bottom one looks like Setaria faberi.

I agree that the first one looks like little bluestem, though here it tends to grow in drier, sandy areas, so I find it interesting that it was planted in a rain garden.

Babs, thank you. It was planted near the curb on the high side of the rain garden, so it was in the driest area. That being said, I did a quick search and little bluestem is listed on some rain garden plant lists.

I'm disappointed that the other grass may be non-native :(