Las Pilitas Nursery with stores in Escondido and Santa Margarita has lists of groundcovers that should do well in your backyard with a steep slope. They have lists divided into those that grow less than 1 foot high, those 1 to 2 feet high and those taller than 2 feet. Here are a few that grow 1 foot or less high:
Arctostaphylos uva-ursi (Kinnikinnick) is shrub that grows well in sun, part shade and shade. Las Pilitas lists several varieties that have particular features that you might like:
Ceanothus hearstiorum (Hearst ranch buckbrush) grows no higher than 2 to 3 inches and in part shade. Here are photos and more information from Las Pilitas, Theodore Payne Foundation in Sun Valley, CA and Yerba Buena Nursery in Woodside, CA.
Corethrogyne filaginifolia (Common sandaster) grows on slopes in part shade. Las Pilitas has a a variety, Silver Carpet, that grows to less than 18 inches. You can see more photos and information from Southern California Research Learning Center.
Monardella macrantha (Hummingbird mint) grows in part shade and has red flowers that attract hummingbirds. Here are photos and more information from Las Pilitas, Theodore Payne Foundation and Yerba Buena Nursery.