Hello pwade and welcome to garden.org. We will need to know where you are to be able to advise you on suitable plants. Please fill in your profile with your location including city/state/country? Just a zone doesn't help much.
Couple more questions - is there irrigation on your hills or are you looking for drought-tolerant plants? In any case you need to be able to irrigate to get new plants established. If they don't have a good deep root system by next summer, they will just fry. So fall planting is a great idea if you are still able to plant where you are.
Also, do you want all one type of groundcover? That's a very large area to plant in one thing. A "monoculture" is a bit of a dangerous way to go, since if something goes wrong you could lose the whole thing. Various types of groundcovers, mixed into a tapestry effect can be beautiful and much more sure of success, too.
