Mystery grass - Scirpus sp.?

A very striking grass is growing at my house.  It looks a lot like Scirpus cyperinus (woolgrass), which would make it a VA native.  However, woolgrass is supposed to grow in wet meadows and swamps.  This stuff grows in clay soil in medium/dry meadows and roadsides, in full to part sun.  I'm pretty sure it's in the genus Scirpus, at least.  Can anyone ID my mystery grass?

This stuff would be great as an ornamental.  It reminds me of fireworks.  I don't even like most ornamental grasses, but I took a lot of pictures of this because it looks so cool.  Also, did I mention it seems to like clay soil?

It grows in clumps and is about 5 feet tall.

It seems to be a sedge, rather than a true grass.  My father observed that the stems have a triangular cross section near the base and applied this little rhyme (which I think he learned in a college botany class in the '70s):
Sedges have edges;
rushes are round.
Grasses are hollow
like holes in the ground.

Any idea what this plant is?