When I started to let the dogs out again later that afternoon, I found several wasps buzzing around the front porch. I let the dogs out another door, then grabbed a can of wasp & hornet killer and started spraying.
I almost bit off more than I could chew, because there were a lot more wasps than I saw the first time. I sprayed at least half a can of poison onto the porch to take them out. I later counted 11 corpses, though I think a few fell out the window and some are probably behind stuff. I went outside and sprayed the rest of the can taking out a few more wasps that were hanging around.
I didn't see a nest anywhere. Hopefully I managed to kill enough of them to stave off a full-fledged invasion. I need to buy more poison tomorrow, just in case. I usually buy pyrethroid-based poison, which is harmless to birds and most mammals (except cats), but is extremely effective against insects. (Back in Vista, where I didn't have to worry about pets, I used my own concoction of diazinon, chlorpyrifos and malathion. It's super effective!)