Well, after fiddling around with it, I discovered the breaker that was LABELED for the basement actually is for... well... nothing, as far as I can tell. O_O Flipped both switches off, went around the house, can't find ANYTHING that it affected. Soooo... no idea there. But I did find the switch that shuts the basement down. It's the same breaker that controls the garage, but the garage is on one switch and the basement is on the other switch, the entire basement controlled by the one switch on the breaker. Would probably be nice to have both on a GFCI breaker anyway, but it doesn't feel right that the garage is controled by the same breaker that controls the basement, which will be drawing a LOT of power with the greenhouse down there. That coupled with power tools and the shop lights in the garage sounds like a recipe for lots of tripped breakers to me, but maybe not since they're on separate switches. I don't know. LOL.
Another question, though. I assume the ground bar is where all those white wires come up and are screwed down in the bottom of the above picture, right?
I'm starting to wonder if this all will just necessitate the hiring of an electrician. When we bought the place, the inspector noted there were no GFCI outlets anywhere in the house - obviously a safety violation. So before we even moved in, an electrician came through and did his own inspection and installed a bunch of them throughout the house. Unfortunately, he didn't install any in the basement, which is required according to that HD page. Interesting...