Ferns are going to struggle in those conditions.

Look into
Epimedium
Euphorbia
Carex morrowii or others

Of course you will have to water anything the first year.

hmm. lots of sun, lousy growing conditions...

nasturtiums are an annual, though they may well either hang on, or reseed in your climate. and 'miserable' is what they like best. I have some growing in the patch of dirt between my walk and my neighbor's- it's maybe 4" wide, 4" deep, and gets no care at all...but they're thriving, they're edible-related to watercress, the young leaves are merely peppery, the older leaves tend to be downright bitter, and get kind of spotty looking (not something you want in a salad) and the bright yellow and orange flowers are downright hot!

there are also a number of species of sedums that might do well there with just some roughing up of the soil and some mulch- golden acres starts out as rosettes that turn into strings of diamond-shaped leaves, and puts out tiny star-shaped yellow flowers. dragon's blood has red-edged foliage, and wine-red blossoms, autumn's Joy is actually a standing version (2 feet tall) that makes flowerheads that change from nearly white to pink to rust over time, and dry on the plant.

all of the sedums root easily (get a potof them, break the rootball up into four quarters, plant separately- then take all the broken off bits, and stick them in a tray of damp sand, and leave it in the shade for a week- presto, baby plants!) and so give you a lot of bang for your buck.

a related species are the old fahsioned hens-and-chicks, which don't take over quite so fast, but come in some wild color combinations :)