Actually, having never lived out west I don't know all that much about rolling blackouts, but now I do thanks to the wonders of wikipedia :) I was interested in how grids are divided up since it's different across the country. In my area in MN we have two separate companies supplying my city alone, mine is the rural neighborhoods and is wind power (yay!) and the other is the "city" company. But in other states a single entity sometimes runs an entire state, or just a county like you mention.