Maybe use Berkely Sedge (clump grass) as a ground cover along with seaside daisy if you have semi-shade. Native Maidenhair fern would soften edges and you could add some interesting California succulents/dudleya, depending on exposure (some sun?). You might want to consider planting a narrow patio tree such as the Catalina Ironwood if the top of the tree would have sunlight. If not, a vine (native Chaparral Honeysuckle) growing up the fence could be used instead of a tree.

A trip to a nursery specializing in California natives will save you time and money needed to change soil and moisture to support typical acid/water shade gardens.