As a former S. Californian, there are lots of ground covers available, including fire resistant plants - with all those trees, I'd definitely look for those. I'd go to your nearest nursery and ask for what is best in your area.

In your first thumbnail pic it looks like you got a lot of rocks. Instead of trying to get rid of them maybe use them to multi tiered rock wall garden https://www.houzz.com/photos/tiered-landscape-with-rocks-phbr0lbl-bl~l_79697?fi=8
Since you get direct sunlight spread mulch on top so the soil doesn't dry out as fast. We particularly like the red mulch. Really highlights the plants and shows them off

We are struggling with the same issue and have decided to go with stone terracing.

In this weekend alone we spent a small fortune ($40.00 approx.) in buying potting soil and red mulch. We brought the soil because our trees have those smalls roots that creep along the surface, and instead tearing them up we simply layed additional soil over them. Wish us luck :)