To me it looks like Early Blight - the concentric rings being the best identifying symptom I can see.

This is a fungal infection. If you search the forums for Early Blight treatment and fungicides you'll find a host of treatment options described in detail.

Suggest removing affected foliage immediately, and spray with a fungicide, maybe Daconil.

As I suspected. Albeit, a little befuddlling, given recent weather conditions - essentially no rain, until today ironically, and I really have watered very sparsely. Weird that it seemed to originate on my well established, well mulched rose bush as well. Dang.
I believe the rose is too far gone. Thinking about deadheading to the ground and disposing of it all, in addition to the mulch below.
As for the maters, as suggested, I removed as much affected foliage as I could, and thinned out below and between plants. Really had to butcher a couple badly. Then, since it finally dried up today, applied Daconil. Don't have high hopes, though. Been too busy, and let it get out of control before diagnosis. :(

Thanks, all!